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1.
  • Alavioon, Ghazal, et al. (författare)
  • Selection for longer lived sperm within ejaculate reduces reproductive ageing in offspring
  • 2019
  • Ingår i: Evolution Letters. - : Oxford University Press (OUP). - 2056-3744. ; 3:2, s. 198-206
  • Tidskriftsartikel (refereegranskat)abstract
    • Males produce numerous sperm in a single ejaculate that greatly outnumber their potential egg targets. Recent studies found that phenotypic and genotypic variation among sperm in a single ejaculate of a male affects the fitness and performance of the resulting offspring. Specifically, within-ejaculate sperm selection for sperm longevity increased the performance of the resulting offspring in several key life-history traits in early life. Because increased early-life reproductive performance often correlates with rapid ageing, it is possible that within-ejaculate sperm selection increases early-life fitness at the cost of accelerated senescence. Alternatively, within-ejaculate sperm selection could improve offspring quality throughout the life cycle, including reduced age-specific deterioration. We tested the two alternative hypotheses in an experimental setup using zebrafish Danio rerio. We found that within-ejaculate sperm selection for sperm longevity reduced age-specific deterioration of fecundity and offspring survival but had no effect on fertilization success in males. Remarkably, we found an opposing effect of within-ejaculate sperm selection on female fecundity, where selection for sperm longevity resulted in increased early-life performance followed by a slow decline, while females sired by unselected sperm started low but increased their fecundity with age. Intriguingly, within-ejaculate sperm selection also reduced the age-specific decline in fertilization success in females, suggesting that selection for sperm longevity improves at least some aspects of female reproductive ageing. These results demonstrate that within-ejaculate variation in sperm phenotype contributes to individual variation in animal life histories in the two sexes and may have important implications for assisted fertilization programs in livestock and humans.
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2.
  • Baur, Julian, et al. (författare)
  • Heat stress reveals a fertility debt owing to postcopulatory sexual selection
  • 2023
  • Ingår i: Evolution Letters. - : Oxford University Press (OUP). - 2056-3744. ; 8:1, s. 101-113
  • Tidskriftsartikel (refereegranskat)abstract
    • Climates are changing rapidly, demanding equally rapid adaptation of natural populations. Whether sexual selection can aid such adaptation is under debate; while sexual selection should promote adaptation when individuals with high mating success are also best adapted to their local surroundings, the expression of sexually selected traits can incur costs. Here we asked what the demographic consequences of such costs may be once climates change to become harsher and the strength of natural selection increases. We first adopted a classic life history theory framework, incorporating a trade-off between reproduction and maintenance, and applied it to the male germline to generate formalized predictions for how an evolutionary history of strong postcopulatory sexual selection (sperm competition) may affect male fertility under acute adult heat stress. We then tested these predictions by assessing the thermal sensitivity of fertility (TSF) in replicated lineages of seed beetles maintained for 68 generations under three alternative mating regimes manipulating the opportunity for sexual and natural selection. In line with the theoretical predictions, we find that males evolving under strong sexual selection suffer from increased TSF. Interestingly, females from the regime under strong sexual selection, who experienced relaxed selection on their own reproductive effort, had high fertility in benign settings but suffered increased TSF, like their brothers. This implies that female fertility and TSF evolved through genetic correlation with reproductive traits sexually selected in males. Paternal but not maternal heat stress reduced offspring fertility with no evidence for adaptive transgenerational plasticity among heat-exposed offspring, indicating that the observed effects may compound over generations. Our results suggest that trade-offs between fertility and traits increasing success in postcopulatory sexual selection can be revealed in harsh environments. This can put polyandrous species under immediate risk during extreme heat waves expected under future climate change.
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3.
  • Baur, Julian, et al. (författare)
  • Heat stress reveals a fertility debt owing to postcopulatory sexual selection
  • 2024
  • Ingår i: Evolution Letters. - : Oxford University Press. - 2056-3744. ; 8:1, s. 101-113
  • Tidskriftsartikel (refereegranskat)abstract
    • Climates are changing rapidly, demanding equally rapid adaptation of natural populations. Whether sexual selection can aid such adaptation is under debate; while sexual selection should promote adaptation when individuals with high mating success are also best adapted to their local surroundings, the expression of sexually selected traits can incur costs. Here we asked what the demographic consequences of such costs may be once climates change to become harsher and the strength of natural selection increases. We first adopted a classic life history theory framework, incorporating a trade-off between reproduction and maintenance, and applied it to the male germline to generate formalized predictions for how an evolutionary history of strong postcopulatory sexual selection (sperm competition) may affect male fertility under acute adult heat stress. We then tested these predictions by assessing the thermal sensitivity of fertility (TSF) in replicated lineages of seed beetles maintained for 68 generations under three alternative mating regimes manipulating the opportunity for sexual and natural selection. In line with the theoretical predictions, we find that males evolving under strong sexual selection suffer from increased TSF. Interestingly, females from the regime under strong sexual selection, who experienced relaxed selection on their own reproductive effort, had high fertility in benign settings but suffered increased TSF, like their brothers. This implies that female fertility and TSF evolved through genetic correlation with reproductive traits sexually selected in males. Paternal but not maternal heat stress reduced offspring fertility with no evidence for adaptive transgenerational plasticity among heat-exposed offspring, indicating that the observed effects may compound over generations. Our results suggest that trade-offs between fertility and traits increasing success in postcopulatory sexual selection can be revealed in harsh environments. This can put polyandrous species under immediate risk during extreme heat waves expected under future climate change.
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4.
  • Berdan, Emma L, 1983, et al. (författare)
  • A large chromosomal inversion shapes gene expression in seaweed flies (Coelopa frigida)
  • 2021
  • Ingår i: EVOLUTION LETTERS. - : Oxford University Press (OUP). - 2056-3744. ; 5:6, s. 607-624
  • Tidskriftsartikel (refereegranskat)abstract
    • Inversions often underlie complex adaptive traits, but the genic targets inside them are largely unknown. Gene expression profiling provides a powerful way to link inversions with their phenotypic consequences. We examined the effects of the Cf-Inv(1) inversion in the seaweed fly Coelopa frigida on gene expression variation across sexes and life stages. Our analyses revealed that Cf-Inv(1) shapes global expression patterns, most likely via linked variation, but the extent of this effect is variable, with much stronger effects in adults than larvae. Furthermore, within adults, both common as well as sex-specific patterns were found. The vast majority of these differentially expressed genes mapped to Cf-Inv(1). However, genes that were differentially expressed in a single context (i.e., in males, females, or larvae) were more likely to be located outside of Cf-Inv(1). By combining our findings with genomic scans for environmentally associated SNPs, we were able to pinpoint candidate variants in the inversion that may underlie mechanistic pathways that determine phenotypes. Together the results of this study, combined with previous findings, support the notion that the polymorphic Cf-Inv(1) inversion in this species is a major factor shaping both coding and regulatory variation resulting in highly complex adaptive effects.
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5.
  • Bijl, Wouter, et al. (författare)
  • Butterfly dichromatism primarily evolved via Darwin's, not Wallace's, model
  • 2020
  • Ingår i: Evolution letters. - : Oxford University Press (OUP). - 2056-3744. ; 4:6, s. 545-555
  • Tidskriftsartikel (refereegranskat)abstract
    • Sexual dimorphism is typically thought to result from sexual selection for elaborated male traits, as proposed by Darwin. However, natural selection could reduce expression of elaborated traits in females, as proposed by Wallace. Darwin and Wallace debated the origins of dichromatism in birds and butterflies, and although evidence in birds is roughly equal, if not in favor of Wallace's model, butterflies lack a similar scale of study. Here, we present a large‐scale comparative phylogenetic analysis of the evolution of butterfly coloration, using all European non‐hesperiid butterfly species (n = 369). We modeled evolutionary changes in coloration for each species and sex along their phylogeny, thereby estimating the rate and direction of evolution in three‐dimensional color space using a novel implementation of phylogenetic ridge regression. We show that male coloration evolved faster than female coloration, especially in strongly dichromatic clades, with male contribution to changes in dichromatism roughly twice that of females. These patterns are consistent with a classic Darwinian model of dichromatism via sexual selection on male coloration, suggesting this model was the dominant driver of dichromatism in European butterflies.
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6.
  • Chen, Hwei-yen, 1983-, et al. (författare)
  • Germline mutation rate is elevated in young and old parents in Caenorhabditis remanei
  • 2023
  • Ingår i: Evolution Letters. - : Oxford University Press. - 2056-3744. ; 7:6, s. 478-489
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of parental age on germline mutation rate across generations is not fully understood. While some studies report a positive linear relationship of mutation rate with increasing age, others suggest that mutation rate varies with age but not in a linear fashion. We investigated the effect of parental age on germline mutations by generating replicated mutation accumulation lines in Caenorhabditis remanei at three parental ages ("Young T1" [Day 1], "Peak T2" [Day 2], and "Old T5" [Day 5] parents). We conducted whole-genome resequencing and variant calling to compare differences in mutation rates after three generations of mutation accumulation. We found that Peak T2 lines had an overall reduced mutation rate compared to Young T1 and Old T5 lines, but this pattern of the effect varied depending on the variant impact. Specifically, we found no high-impact variants in Peak T2 lines, and modifiers and up- and downstream gene variants were less frequent in these lines. These results suggest that animals at the peak of reproduction have better DNA maintenance and repair compared to young and old animals. We propose that C. remanei start to reproduce before they optimize their DNA maintenance and repair, trading the benefits of earlier onset of reproduction against offspring mutation load. The increase in offspring mutation load with age likely represents germline senescence. Germline mutations play a key role in evolution through the generation of novel genotypes. Estimating the mutation rate in species, populations, and individuals is one way to understand the relative timeframe of evolutionary processes, for the timing of historical events and for estimating heritability of traits and diseases. Individual age at reproduction is known to affect the number of mutations being transferred into the next generation and generally mutation rate is thought to increase with increasing parental age. However, preventing mutations in germ cells is potentially costly and it may pay off to optimize germline genome repair and maintenance during peak reproductive periods, and relax it during nonpeak periods. This idea has been put forward to explain for example the reduction of gonad size in seasonally reproducing animals during nonreproductive periods and supported by the finding that the mutation rate seems to be higher in teenage men compared to men during their peak reproductive ages. We further tested this idea of a nonlinear relationship between age and mutation rate by performing a mutation accumulation experiment in a short-lived nematode. We kept experimental lines and allowed adults to reproduce at different ages in different lines, with some lines reproducing before, some during, and some after their reproductive peak. We found that mutation rates are higher in nematode lines reproducing before or after the reproductive peak compared to those reproducing during the peak. Our results therefore support the idea that germline genome maintenance and repair is potentially costly and that the mutation rate does not just increase with age but is optimized during the peak reproductive age of an organism.
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7.
  • De Lisle, Stephen P., et al. (författare)
  • Condition dependence and the paradox of missing plasticity costs
  • 2023
  • Ingår i: Evolution Letters. - : Oxford University Press. - 2056-3744. ; 7:2, s. 67-78
  • Tidskriftsartikel (refereegranskat)abstract
    • Phenotypic plasticity plays a key role in adaptation to changing environments. However, plasticity is neither perfect nor ubiquitous, implying that fitness costs may limit the evolution of phenotypic plasticity in nature. The measurement of such costs of plasticity has proved elusive; decades of experiments show that fitness costs of plasticity are often weak or nonexistent. Here, we show that this paradox could potentially be explained by condition dependence. We develop two models differing in their assumptions about how condition dependence arises; both models show that variation in condition can readily mask costs of plasticity even when such costs are substantial. This can be shown simply in a model where plasticity itself evolves condition dependence, which would be expected if costly. Yet similar effects emerge from an alternative model where trait expression itself is condition-dependent. In this more complex model, the average condition in each environment and genetic covariance in condition across environments both determine when costs of plasticity can be revealed. Analogous to the paradox of missing trade-offs between life history traits, our models show that variation in condition can mask costs of plasticity even when costs exist, and suggest this conclusion may be robust to the details of how condition affects trait expression. Our models suggest that condition dependence can also account for the often-observed pattern of elevated plasticity costs inferred in stressful environments, the maintenance of genetic variance in plasticity, and provides insight into experimental and biological scenarios ideal for revealing a cost of phenotypic plasticity.
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8.
  • Dehasque, Marianne, et al. (författare)
  • Inference of natural selection from ancient DNA
  • 2020
  • Ingår i: Evolution Letters. - : JOHN WILEY & SONS LTD. - 2056-3744. ; 4:2, s. 94-108
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Evolutionary processes, including selection, can be indirectly inferred based on patterns of genomic variation among contemporary populations or species. However, this often requires unrealistic assumptions of ancestral demography and selective regimes. Sequencing ancient DNA from temporally spaced samples can inform about past selection processes, as time series data allow direct quantification of population parameters collected before, during, and after genetic changes driven by selection. In this Comment and Opinion, we advocate for the inclusion of temporal sampling and the generation of paleogenomic datasets in evolutionary biology, and highlight some of the recent advances that have yet to be broadly applied by evolutionary biologists. In doing so, we consider the expected signatures of balancing, purifying, and positive selection in time series data, and detail how this can advance our understanding of the chronology and tempo of genomic change driven by selection. However, we also recognize the limitations of such data, which can suffer from postmortem damage, fragmentation, low coverage, and typically low sample size. We therefore highlight the many assumptions and considerations associated with analyzing paleogenomic data and the assumptions associated with analytical methods.
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9.
  • Delmore, Kira E, et al. (författare)
  • Comparative analysis examining patterns of genomic differentiation across multiple episodes of population divergence in birds
  • 2018
  • Ingår i: Evolution letters. - : Oxford University Press (OUP). - 2056-3744. ; 2:2, s. 76-87
  • Tidskriftsartikel (refereegranskat)abstract
    • Heterogeneous patterns of genomic differentiation are commonly documented between closely related populations and there is considerable interest in identifying factors that contribute to their formation. These factors could include genomic features (e.g., areas of low recombination) that promote processes like linked selection (positive or purifying selection that affects linked neutral sites) at specific genomic regions. Examinations of repeatable patterns of differentiation across population pairs can provide insight into the role of these factors. Birds are well suited for this work, as genome structure is conserved across this group. Accordingly, we reestimated relative (FST ) and absolute (dXY ) differentiation between eight sister pairs of birds that span a broad taxonomic range using a common pipeline. Across pairs, there were modest but significant correlations in window-based estimates of differentiation (up to 3% of variation explained for FST and 26% for dXY ), supporting a role for processes at conserved genomic features in generating heterogeneous patterns of differentiation; processes specific to each episode of population divergence likely explain the remaining variation. The role genomic features play was reinforced by linear models identifying several genomic variables (e.g., gene densities) as significant predictors of FST and dXY repeatability. FST repeatability was higher among pairs that were further along the speciation continuum (i.e., more reproductively isolated) providing further insight into how genomic differentiation changes with population divergence; early stages of speciation may be dominated by positive selection that is different between pairs but becomes integrated with processes acting according to shared genomic features as speciation proceeds.
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10.
  • DiLeo, Michelle F., et al. (författare)
  • Landscape permeability and individual variation in a dispersal-linked gene jointly determine genetic structure in the Glanville fritillary butterfly
  • 2018
  • Ingår i: Evolution Letters. - : JOHN WILEY & SONS LTD. - 2056-3744. ; 2:6, s. 544-556
  • Tidskriftsartikel (refereegranskat)abstract
    • There is now clear evidence that species across a broad range of taxa harbor extensive heritable variation in dispersal. While studies suggest that this variation can facilitate demographic outcomes such as range expansion and invasions, few have considered the consequences of intraspecific variation in dispersal for the maintenance and distribution of genetic variation across fragmented landscapes. Here, we examine how landscape characteristics and individual variation in dispersal combine to predict genetic structure using genomic and spatial data from the Glanville fritillary butterfly. We used linear and latent factor mixed models to identify the landscape features that best predict spatial sorting of alleles in the dispersal-related gene phosphoglucose isomerase (Pgi). We next used structural equation modeling to test if variation in Pgi mediated gene flow as measured by F-st at putatively neutral loci. In a year when the population was recovering following a large decline, individuals with a genotype associated with greater dispersal ability were found at significantly higher frequencies in populations isolated by water and forest, and these populations showed lower levels of genetic differentiation at neutral loci. These relationships disappeared in the next year when metapopulation density was high, suggesting that the effects of individual variation are context dependent. Together our results highlight that (1) more complex aspects of landscape structure beyond just the configuration of habitat can be important for maintaining spatial variation in dispersal traits and (2) that individual variation in dispersal plays a key role in maintaining genetic variation across fragmented landscapes.
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11.
  • Egan, Paul A., et al. (författare)
  • Pollinators and herbivores interactively shape selection on strawberry defence and attraction
  • 2021
  • Ingår i: Evolution Letters. - : John Wiley & Sons. - 2056-3744. ; 5:6, s. 636-643
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Tripartite interactions between plants, herbivores, and pollinators hold fitness consequences for most angiosperms. However, little is known on how plants evolve in response-and in particular what the net selective outcomes are for traits of shared relevance to pollinators and herbivores. In this study, we manipulated herbivory ("presence" and "absence" treatments) and pollination ("open" and "hand pollination" treatments) in a full factorial common-garden experiment with woodland strawberry (Fragaria vesca L.). This design allowed us to quantify the relative importance and interactive effects of herbivore- and pollinator-mediated selection on nine traits related to plant defence and attraction. Our results showed that pollinators imposed stronger selection than herbivores on traits related to both direct and indirect (i.e., tritrophic) defence. However, conflicting selection was imposed on inflorescence density: a trait that appears to be shared by herbivores and pollinators as a host plant signal. However, in all cases, selection imposed by one agent depended largely on the presence or ecological effect of the other, suggesting that dynamic patterns of selection could be a common outcome of these interactions in natural populations. As a whole, our findings highlight the significance of plant-herbivore-pollinator interactions as potential drivers of evolutionary change, and reveal that pollinators likely play an underappreciated role as selective agents on direct and in direct plant defence.
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12.
  • Feiner, Nathalie (författare)
  • Evolutionary lability in Hox cluster structure and gene expression in Anolis lizards
  • 2019
  • Ingår i: Evolution letters. - : Oxford University Press (OUP). - 2056-3744. ; 3:5, s. 474-484
  • Tidskriftsartikel (refereegranskat)abstract
    • Hox genes orchestrate development by patterning the embryonic axis. Vertebrate Hox genes are arranged in four compact clusters, and the spacing between genes is assumed to be crucial for their function. The genomes of squamate reptiles are unusually rich and variable in transposable elements (TEs), and it has been suggested that TE invasion is responsible for the Hox cluster expansion seen in snakes and lizards. Using de novo TE prediction on 17 genomes of lizards and snakes, I show that TE content of Hox clusters are generally 50% lower than genome‐wide TE levels. However, two distantly related lizards of the species‐rich genus Anolis have Hox clusters with a TE content that approaches genomic levels. The age distribution of TEs in Anolis lizards revealed that peaks of TE activity broadly coincide with speciation events. In accordance with theoretical models of Hox cluster regulation, I find that Anolis species with many TEs in their Hox clusters show aberrant Hox gene expression patterns, suggesting a functional link between TE accumulation and embryonic development. These results are consistent with the hypothesis that TEs play a role in developmental processes as well as in evolutionary diversifications.
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13.
  • Gómez-Llano, Miguel, et al. (författare)
  • Male harm suppresses female fitness, affecting the dynamics of adaptation and evolutionary rescue
  • 2024
  • Ingår i: Evolution Letters. - : Oxford University Press. - 2056-3744. ; 8:1, s. 149-160
  • Tidskriftsartikel (refereegranskat)abstract
    • One of the most pressing questions we face as biologists is to understand how climate change will affect the evolutionary dynamics of natural populations and how these dynamics will in turn affect population recovery. Increasing evidence shows that sexual selection favors population viability and local adaptation. However, sexual selection can also foster sexual conflict and drive the evolution of male harm to females. Male harm is extraordinarily widespread and has the potential to suppress female fitness and compromise population growth, yet we currently ignore its net effects across taxa or its influence on local adaptation and evolutionary rescue. We conducted a comparative meta-analysis to quantify the impact of male harm on female fitness and found an overall negative effect of male harm on female fitness. Negative effects seem to depend on proxies of sexual selection, increasing inversely to the female relative size and in species with strong sperm competition. We then developed theoretical models to explore how male harm affects adaptation and evolutionary rescue. We show that, when sexual conflict depends on local adaptation, population decline is reduced, but at the cost of slowing down genetic adaptation. This trade-off suggests that eco-evolutionary feedback on sexual conflict can act like a double-edged sword, reducing extinction risk by buffering the demographic costs of climate change, but delaying genetic adaptation. However, variation in the mating system and male harm type can mitigate this trade-off. Our work shows that male harm has widespread negative effects on female fitness and productivity, identifies potential mechanistic factors underlying variability in such costs across taxa, and underscores how acknowledging the condition-dependence of male harm may be important to understand the demographic and evolutionary processes that impact how species adapt to environmental change.
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14.
  • Grieshop, Karl, et al. (författare)
  • Selection in males purges the mutation load on female fitness
  • 2021
  • Ingår i: Evolution Letters. - : John Wiley & Sons. - 2056-3744. ; 5:4, s. 328-343
  • Tidskriftsartikel (refereegranskat)abstract
    • Theory predicts that the ability of selection and recombination to purge mutation load is enhanced if selection against deleterious genetic variants operates more strongly in males than females. However, direct empirical support for this tenet is limited, in part because traditional quantitative genetic approaches allow dominance and intermediate-frequency polymorphisms to obscure the effects of the many rare and partially recessive deleterious alleles that make up the main part of a population's mutation load. Here, we exposed the partially recessive genetic load of a population of Callosobruchus maculatus seed beetles via successive generations of inbreeding, and quantified its effects by measuring heterosis-the increase in fitness experienced when masking the effects of deleterious alleles by heterozygosity-in a fully factorial sex-specific diallel cross among 16 inbred strains. Competitive lifetime reproductive success (i.e., fitness) was measured in male and female outcrossed F(1)s as well as inbred parental "selfs," and we estimated the 4 x 4 male-female inbred-outbred genetic covariance matrix for fitness using Bayesian Markov chain Monte Carlo simulations of a custom-made general linear mixed effects model. We found that heterosis estimated independently in males and females was highly genetically correlated among strains, and that heterosis was strongly negatively genetically correlated to outbred male, but not female, fitness. This suggests that genetic variation for fitness in males, but not in females, reflects the amount of (partially) recessive deleterious alleles segregating at mutation-selection balance in this population. The population's mutation load therefore has greater potential to be purged via selection in males. These findings contribute to our understanding of the prevalence of sexual reproduction in nature and the maintenance of genetic variation in fitness-related traits.
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15.
  • Hansen Wheat, Christina, et al. (författare)
  • Morphology does not covary with predicted behavioral correlations of the domestication syndrome in dogs
  • 2020
  • Ingår i: Evolution Letters. - : Oxford University Press (OUP). - 2056-3744. ; 4:3, s. 189-199
  • Tidskriftsartikel (refereegranskat)abstract
    • Domesticated animals display suites of altered morphological, behavioral, and physiological traits compared to their wild ancestors, a phenomenon known as the domestication syndrome (DS). Because these alterations are observed to co-occur across a wide range of present day domesticates, the traits within the DS are assumed to covary within species and a single developmental mechanism has been hypothesized to cause the observed co-occurrence. However, due to the lack of formal testing it is currently not well-resolved if the traits within DS actually covary. Here, we test the hypothesis that the presence of the classic morphological domestication traits white pigmentation, floppy ears, and curly tails predict the strength of behavioral correlations in support of the DS in 78 dog breeds. Contrary to the expectations of covariation among DS traits, we found that morphological traits did not covary among themselves, nor did they predict the strength of behavioral correlations among dog breeds. Further, the number of morphological traits in a breed did not predict the strength of behavioral correlations. Our results thus contrast with the hypothesis that the DS arises due to a shared underlying mechanism, but more importantly, questions if the morphological traits embedded in the DS are actual domestication traits or postdomestication improvement traits. For dogs, it seems highly likely that strong selection for breed specific morphological traits only happened recently and in relation to breed formation. Present day dogs therefore have limited bearing of the initial selection pressures applied during domestication and we should reevaluate our expectations of the DS accordingly.
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16.
  • Hearn, K. E., et al. (författare)
  • Differing associations between sex determination and sex-linked inversions in two ecotypes of Littorina saxatilis
  • 2022
  • Ingår i: Evolution Letters. - : Oxford University Press (OUP). - 2056-3744. ; 6:5, s. 358-74
  • Tidskriftsartikel (refereegranskat)abstract
    • Sexual antagonism is a common hypothesis for driving the evolution of sex chromosomes, whereby recombination suppression is favored between sexually antagonistic loci and the sex-determining locus to maintain beneficial combinations of alleles. This results in the formation of a sex-determining region. Chromosomal inversions may contribute to recombination suppression but their precise role in sex chromosome evolution remains unclear. Because local adaptation is frequently facilitated through the suppression of recombination between adaptive loci by chromosomal inversions, there is potential for inversions that cover sex-determining regions to be involved in local adaptation as well, particularly if habitat variation creates environment-dependent sexual antagonism. With these processes in mind, we investigated sex determination in a well-studied example of local adaptation within a species: the intertidal snail, Littorina saxatilis. Using SNP data from a Swedish hybrid zone, we find novel evidence for a female-heterogametic sex determination system that is restricted to one ecotype. Our results suggest that four putative chromosomal inversions, two previously described and two newly discovered, span the putative sex chromosome pair. We determine their differing associations with sex, which suggest distinct strata of differing ages. The same inversions are found in the second ecotype but do not show any sex association. The striking disparity in inversion-sex associations between ecotypes that are connected by gene flow across a habitat transition that is just a few meters wide indicates a difference in selective regime that has produced a distinct barrier to the spread of the newly discovered sex-determining region between ecotypes. Such sex chromosome-environment interactions have not previously been uncovered in L. saxatilis and are known in few other organisms. A combination of both sex-specific selection and divergent natural selection is required to explain these highly unusual patterns.
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17.
  • Hollander, Johan, et al. (författare)
  • Are assortative mating and genital divergence driven by reinforcement?
  • 2018
  • Ingår i: Evolution Letters. - : Oxford University Press (OUP). - 2056-3744. ; 2:6, s. 557-566
  • Tidskriftsartikel (refereegranskat)abstract
    • The evolution of assortative mating is a key part of the speciation process. Stronger assortment, or greater divergence in mating traits, between species pairs with overlapping ranges is commonly observed, but possible causes of this pattern of reproductive character displacement are difficult to distinguish. We use a multidisciplinary approach to provide a rare example where it is possible to distinguish among hypotheses concerning the evolution of reproductive character displacement. We build on an earlier comparative analysis that illustrated a strong pattern of greater divergence in penis form between pairs of sister species with overlapping ranges than between allopatric sister-species pairs, in a large clade of marine gastropods (Littorinidae). We investigate both assortative mating and divergence in male genitalia in one of the sister-species pairs, discriminating among three contrasting processes each of which can generate a pattern of reproductive character displacement: reinforcement, reproductive interference and the Templeton effect. We demonstrate reproductive character displacement in assortative mating, but not in genital form between this pair of sister species and use demographic models to distinguish among the different processes. Our results support a model with no gene flow since secondary contact and thus favor reproductive interference as the cause of reproductive character displacement for mate choice, rather than reinforcement. High gene flow within species argues against the Templeton effect. Secondary contact appears to have had little impact on genital divergence.
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18.
  • Kemppainen, Petri, et al. (författare)
  • Accounting for heteroscedasticity and censoring in chromosome partitioning analyses
  • 2018
  • Ingår i: Evolution Letters. - : JOHN WILEY & SONS LTD. - 2056-3744. ; 2:6, s. 599-609
  • Tidskriftsartikel (refereegranskat)abstract
    • A fundamental assumption in quantitative genetics is that traits are controlled by many loci of small effect. Using genomic data, this assumption can be tested using chromosome partitioning analyses, where the proportion of genetic variance for a trait explained by each chromosome (h(c)(2)), is regressed on its size. However, as h(c)(2)-estimates are necessarily positive (censoring) and the variance increases with chromosome size (heteroscedasticity), two fundamental assumptions of ordinary least squares (OLS) regression are violated. Using simulated and empirical data we demonstrate that these violations lead to incorrect inference of genetic architecture. The degree of bias depends mainly on the number of chromosomes and their size distribution and is therefore specific to the species; using published data across many different species we estimate that not accounting for this effect overall resulted in 28% false positives. We introduce a new and computationally efficient resampling method that corrects for inflation caused by heteroscedasticity and censoring and that works under a large range of dataset sizes and genetic architectures in empirical datasets. Our new method substantially improves the robustness of inferences from chromosome partitioning analyses.
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19.
  • Le Moan, Alan, et al. (författare)
  • Coupling of twelve putative chromosomal inversions maintains a strong barrier to gene flow between snail ecotypes
  • 2024
  • Ingår i: EVOLUTION LETTERS. - 2056-3744.
  • Tidskriftsartikel (refereegranskat)abstract
    • Chromosomal rearrangements can lead to the coupling of reproductive barriers, but whether and how they contribute to the completion of speciation remains unclear. Marine snails of the genus Littorina repeatedly form hybrid zones between populations segregating for multiple inversion arrangements, providing opportunities to study their barrier effects. Here, we analyzed 2 adjacent transects across hybrid zones between 2 ecotypes of Littorina fabalis ("large" and "dwarf") adapted to different wave exposure conditions on a Swedish island. Applying whole-genome sequencing, we found 12 putative inversions on 9 of 17 chromosomes. Nine of the putative inversions reached near differential fixation between the 2 ecotypes, and all were in strong linkage disequilibrium. These inversions cover 20% of the genome and carry 93% of divergent single nucleotide polymorphisms (SNPs). Bimodal hybrid zones in both transects indicated that the 2 ecotypes of Littorina fabalis maintain their genetic and phenotypic integrity following contact. The bimodality reflects the strong coupling between inversion clines and the extension of the barrier effect across the whole genome. Demographic inference suggests that coupling arose during a period of allopatry and has been maintained for > 1,000 generations after secondary contact. Overall, this study shows that the coupling of multiple chromosomal inversions contributes to strong reproductive isolation. Notably, 2 of the putative inversions overlap with inverted genomic regions associated with ecotype differences in a closely related species (Littorina saxatilis), suggesting the same regions, with similar structural variants, repeatedly contribute to ecotype evolution in distinct species.
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20.
  • Lind, Martin I., Dr, 1980-, et al. (författare)
  • Environmental variation mediates the evolution of anticipatory parental effects
  • 2020
  • Ingår i: Evolution Letters. - Oxford : John Wiley & Sons. - 2056-3744. ; 4:4, s. 371-381
  • Tidskriftsartikel (refereegranskat)abstract
    • Theory maintains that when future environment is predictable, parents should adjust the phenotype of their offspring to match the anticipated environment. The plausibility of positive anticipatory parental effects is hotly debated and the experimental evidence for the evolution of such effects is currently lacking. We experimentally investigated the evolution of anticipatory maternal effects in a range of environments that differ drastically in how predictable they are. Populations of the nematode Caenorhabditis remanei, adapted to 20°C, were exposed to a novel temperature (25°C) for 30 generations with either positive or zero correlation between parent and offspring environment. We found that populations evolving in novel environments that were predictable across generations evolved a positive anticipatory maternal effect, because they required maternal exposure to 25°C to achieve maximum reproduction in that temperature. In contrast, populations evolving under zero environmental correlation had lost this anticipatory maternal effect. Similar but weaker patterns were found if instead rate-sensitive population growth was used as a fitness measure. These findings demonstrate that anticipatory parental effects evolve in response to environmental change so that ill-fitting parental effects can be rapidly lost. Evolution of positive anticipatory parental effects can aid population viability in rapidly changing but predictable environments. © 2020 The Authors. Evolution Letters published by Wiley Periodicals LLC on behalf of Society for the Study of Evolution (SSE) and European Society for Evolutionary Biology (ESEB).
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21.
  • Lind, Martin I., Dr, et al. (författare)
  • Experimentally reduced insulin/IGF‐1 signaling in adulthood extends lifespan of parents and improves Darwinian fitness of their offspring
  • 2019
  • Ingår i: Evolution Letters. - : Oxford University Press (OUP). - 2056-3744. ; 3:2, s. 207-216
  • Tidskriftsartikel (refereegranskat)abstract
    • Classical theory maintains that ageing evolves via energy trade-offs between reproduction and survival leading to accumulation of unrepaired cellular damage with age. In contrast, the emerging new theory postulates that ageing evolves because of deleterious late-life hyper-function of reproduction-promoting genes leading to excessive biosynthesis in late-life. The hyper-function theory uniquely predicts that optimizing nutrient-sensing molecular signaling in adulthood can simultaneously postpone ageing and increase Darwinian fitness. Here, we show that reducing evolutionarily conserved insulin/IGF-1 nutrient-sensing signaling via daf-2 RNA interference (RNAi) fulfils this prediction in Caenorhabditis elegans nematodes. Long-lived daf-2 RNAi parents showed normal fecundity as self-fertilizing hermaphrodites and improved late-life reproduction when mated to males. Remarkably, the offspring of daf-2 RNAi parents had higher Darwinian fitness across three different genotypes. Thus, reduced nutrient-sensing signaling in adulthood improves both parental longevity and offspring fitness supporting the emerging view that suboptimal gene expression in late-life lies at the heart of ageing.
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22.
  • Lundberg, Max, et al. (författare)
  • Genetic differences between willow warbler migratory phenotypes are few and cluster in large haplotype blocks
  • 2017
  • Ingår i: Evolution Letters. - : John Wiley & Sons. - 2056-3744. ; 1:3, s. 155-168
  • Tidskriftsartikel (refereegranskat)abstract
    • It is well established that differences in migratory behavior between populations of songbirds have a genetic basis but the actual genes underlying these traits remains largely unknown. In an attempt to identify such candidate genes we de novo assembled the genome of the willow warbler Phylloscopus trochilus, and used whole-genome resequencing and a SNP array to associate genomic variation with migratory phenotypes across two migratory divides around the Baltic Sea that separate SW migrating P. t. trochilus wintering in western Africa and SSE migrating P. t. acredula wintering in eastern and southern Africa. We found that the genomes of the two migratory phenotypes lack clear differences except for three highly differentiated regions located on chromosomes 1, 3, and 5 (containing 146, 135, and 53 genes, respectively). Within each migratory phenotype we found virtually no differences in allele frequencies for thousands of SNPs, even when comparing geographically distant populations breeding in Scandinavia and Far East Russia (>6000 km). In each of the three differentiated regions, multidimensional scaling-based clustering of SNP genotypes from more than 1100 individuals demonstrates the presence of distinct haplotype clusters that are associated with each migratory phenotype. In turn, this suggests that recombination is absent or rare between haplotypes, which could be explained by inversion polymorphisms. Whereas SNP alleles on chromosome 3 correlate with breeding altitude and latitude, the allele distribution within the regions on chromosomes 1 and 5 perfectly matches the geographical distribution of the migratory phenotypes. The most differentiated 10 kb windows and missense mutations within these differentiated regions are associated with genes involved in fatty acid synthesis, possibly representing physiological adaptations to the different migratory strategies. The ∼200 genes in these regions, of which several lack described function, will direct future experimental and comparative studies in the search for genes that underlie important migratory traits.
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23.
  • Medina, Iliana, et al. (författare)
  • From cryptic to colorful : Evolutionary decoupling of larval and adult color in butterflies
  • 2020
  • Ingår i: Evolution Letters. - : Oxford University Press (OUP). - 2056-3744. ; 4:1, s. 34-43
  • Tidskriftsartikel (refereegranskat)abstract
    • Many animals undergo complete metamorphosis, where larval forms change abruptly in adulthood. Color change during ontogeny is common, but there is little understanding of evolutionary patterns in these changes. Here, we use data on larval and adult color for 246 butterfly species (61% of all species in Australia) to test whether the evolution of color is coupled between life stages. We show that adults are more variable in color across species than caterpillars and that male adult color has lower phylogenetic signal. These results suggest that sexual selection is driving color diversity in male adult butterflies at a broad scale. Moreover, color similarities between species at the larval stage do not predict color similarities at the adult stage, indicating that color evolution is decoupled between young and adult forms. Most species transition from cryptic coloration as caterpillars to conspicuous coloration as adults, but even species with conspicuous caterpillars change to different conspicuous colors as adults. The use of high-contrast coloration is correlated with body size in caterpillars but not adults. Taken together, our results suggest a change in the relative importance of different selective pressures at different life stages, resulting in the evolutionary decoupling of coloration through ontogeny.
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24.
  • Mestre, Alexandre, et al. (författare)
  • Adaptive colonization across a parasitism-mutualism gradient
  • 2023
  • Ingår i: EVOLUTION LETTERS. - 2056-3744.
  • Tidskriftsartikel (refereegranskat)abstract
    • Adaptive colonization is a process wherein a colonizing population exhibits an adaptive change in response to a novel environment, which may be critical to its establishment. To date, theoretical models of adaptive colonization have been based on single-species introductions. However, given their pervasiveness, symbionts will frequently be co-introduced with their hosts to novel areas. We present an individual-based model to investigate adaptive colonization by hosts and their symbionts across a parasite-mutualist continuum. The host must adapt in order to establish itself in the novel habitat, and the symbiont must adapt to track evolutionary change in the host. First, we classify the qualitative shifts in the outcome that can potentially be driven by non-neutral effects of the symbiont-host interaction into three main types: parasite-driven co-extinction, parasite release, and mutualistic facilitation. Second, we provide a detailed description of a specific example for each type of shift. Third, we disentangle how the interplay between symbiont transmissibility, host migration, and selection strength determines: (a) which type of shift is more likely to occur and (b) the size of the interaction effects necessary to produce it. Overall, we demonstrate the crucial role of host and symbiont dispersal scales in shaping the impacts of parasitism and mutualism on adaptive colonization. Global change is forcing many species to shift their ranges. Colonizing new areas often requires adaptation to novel environmental conditions. Without adaptation, a colonizing population may only be temporarily sustained, thanks to migration. However, although immigrants are poorly adapted to the new habitat, they provide a source of genetic variation that might help the population to adapt to local conditions and persist. Theoretical models have been used to explore this "adaptive colonization" process, but without accounting for the role of symbionts, not withstanding the fact that practically all plant and animal species host symbionts on or inside their bodies. When colonizing new areas, host species also introduce their symbionts. Symbionts range from beneficial mutualists through simple passengers to harmful parasites, so some may help and some may hinder colonization. Furthermore, colonizing symbionts may also experience new selective pressures that would be likely to influence the colonization process. Here we bring together two fields in evolutionary biology-colonization of novel habitats and host-symbiont interactions-to address an important issue for understanding the response of populations to global change: How does the interaction between a colonizing host population and its co-introduced symbionts influence their respective abilities to adapt to new conditions? To do this, we developed a simulation that follows the eco-evolutionary dynamics of a host and its symbiont after being introduced into an empty island with external environmental conditions that differ from those in their source habitats. We considered different types of impact of the symbiont on the host, from strongly negative to strongly positive. Our results show that sometimes neither of the species can establish a population on the island, sometimes both do, and sometimes only the host succeeds. The outcome depends on the dispersal rates of both partners, on the interaction type and strength, and on their need for local adaptation.
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25.
  • Pečnerová, Patrícia, et al. (författare)
  • Mitogenome evolution in the last surviving woolly mammoth population reveals neutral and functional consequences of small population size
  • 2017
  • Ingår i: Evolution Letters. - : Oxford University Press (OUP). - 2056-3744. ; 1:6, s. 292-303
  • Tidskriftsartikel (refereegranskat)abstract
    • The onset of the Holocene was associated with a global temperature increase, which led to a rise in sea levels and isolation of the last surviving population of woolly mammoths on Wrangel Island. Understanding what happened with the population's genetic diversity at the time of the isolation and during the ensuing 6000 years can help clarify the effects of bottlenecks and subsequent limited population sizes in species approaching extinction. Previous genetic studies have highlighted questions about how the Holocene Wrangel population was established and how the isolation event affected genetic diversity. Here, we generated high-quality mitogenomes from 21 radiocarbon-dated woolly mammoths to compare the ancestral large and genetically diverse Late Pleistocene Siberian population and the small Holocene Wrangel population. Our results indicate that mitogenome diversity was reduced to one single haplotype at the time of the isolation, and thus that the Holocene Wrangel Island population was established by a single maternal lineage. Moreover, we show that the ensuing small effective population size coincided with fixation of a nonsynonymous mutation, and a comparative analysis of mutation rates suggests that the evolutionary rate was accelerated in the Holocene population. These results suggest that isolation on Wrangel Island led to an increase in the frequency of deleterious genetic variation, and thus are consistent with the hypothesis that strong genetic drift in small populations leads to purifying selection being less effective in removing deleterious mutations.
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26.
  • Reeve, Andrew Hart, et al. (författare)
  • Population genomics of the island thrush elucidates one of earth's great archipelagic radiations.
  • 2023
  • Ingår i: Evolution letters. - 2056-3744. ; 7:1, s. 24-36
  • Tidskriftsartikel (refereegranskat)abstract
    • Tropical islands are renowned as natural laboratories for evolutionary study. Lineage radiations across tropical archipelagos are ideal systems for investigating how colonization, speciation, and extinction processes shape biodiversity patterns. The expansion of the island thrush across the Indo-Pacific represents one of the largest yet most perplexing island radiations of any songbird species. The island thrush exhibits a complex mosaic of pronounced plumage variation across its range and is arguably the world's most polytypic bird. It is a sedentary species largely restricted to mountain forests, yet it has colonized a vast island region spanning a quarter of the globe. We conducted a comprehensive sampling of island thrush populations and obtained genome-wide SNP data, which we used to reconstruct its phylogeny, population structure, gene flow, and demographic history. The island thrush evolved from migratory Palearctic ancestors and radiated explosively across the Indo-Pacific during the Pleistocene, with numerous instances of gene flow between populations. Its bewildering plumage variation masks a biogeographically intuitive stepping stone colonization path from the Philippines through the Greater Sundas, Wallacea, and New Guinea to Polynesia. The island thrush's success in colonizing Indo-Pacific mountains can be understood in light of its ancestral mobility and adaptation to cool climates; however, shifts in elevational range, degree of plumage variation and apparent dispersal rates in the eastern part of its range raise further intriguing questions about its biology.
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27.
  • Rogell, Björn, et al. (författare)
  • Controlling for body size leads to inferential biases in the biological sciences
  • 2020
  • Ingår i: Evolution Letters. - : Oxford University Press (OUP). - 2056-3744. ; 4:1, s. 73-82
  • Tidskriftsartikel (refereegranskat)abstract
    • Many traits correlate with body size. Studies that seek to uncover the ecological factors that drive evolutionary responses in traits typically examine these responses relative to associated changes in body size using multiple regression analysis. However, it is not well appreciated that in the presence of strongly correlated variables, the partial (i.e., relative) regression coefficients often change sign compared to the original coefficients. Such sign reversals are difficult to interpret in a biologically meaningful way, and could lead to erroneous evolutionary inferences if the true mechanism underlying the sign reversal differed from the proposed mechanism. Here, we use simulations to demonstrate that sign reversal occurs over a wide range of parameter values common in the biological sciences. Further, as a case-in-point, we review the literature on brain size evolution; a field that explores how ecological traits relate to the evolution of relative brain size (brain size relative to body size). We find that most studies show sign reversals and thus that the inferences of many studies in this field may be inconclusive. Finally, we propose some approaches to mitigating this issue.
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28.
  • Ruzicka, Filip, et al. (författare)
  • The search for sexually antagonistic genes : Practical insights from studies of local adaptation and statistical genomics
  • 2020
  • Ingår i: Evolution letters. - : Oxford University Press (OUP). - 2056-3744. ; 4:5, s. 398-415
  • Tidskriftsartikel (refereegranskat)abstract
    • Sexually antagonistic (SA) genetic variation—in which alleles favored in one sex are disfavored in the other—is predicted to be common and has been documented in several animal and plant populations, yet we currently know little about its pervasiveness among species or its population genetic basis. Recent applications of genomics in studies of SA genetic variation have highlighted considerable methodological challenges to the identification and characterization of SA genes, raising questions about the feasibility of genomic approaches for inferring SA selection. The related fields of local adaptation and statistical genomics have previously dealt with similar challenges, and lessons from these disciplines can therefore help overcome current difficulties in applying genomics to study SA genetic variation. Here, we integrate theoretical and analytical concepts from local adaptation and statistical genomics research—including FST and FIS statistics, genome‐wide association studies, pedigree analyses, reciprocal transplant studies, and evolve‐and‐resequence experiments—to evaluate methods for identifying SA genes and genome‐wide signals of SA genetic variation. We begin by developing theoretical models for between‐sex FST and FIS, including explicit null distributions for each statistic, and using them to critically evaluate putative multilocus signals of sex‐specific selection in previously published datasets. We then highlight new statistics that address some of the limitations of FST and FIS, along with applications of more direct approaches for characterizing SA genetic variation, which incorporate explicit fitness measurements. We finish by presenting practical guidelines for the validation and evolutionary analysis of candidate SA genes and discussing promising empirical systems for future work.
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29.
  • Saleh, Dounia, et al. (författare)
  • Genome-wide evolutionary response of European oaks during the Anthropocene
  • 2022
  • Ingår i: Evolution Letters. - : John Wiley & Sons. - 2056-3744. ; 6:1, s. 4-20
  • Tidskriftsartikel (refereegranskat)abstract
    • The pace of tree microevolution during Anthropocene warming is largely unknown. We used a retrospective approach to monitor genomic changes in oak trees since the Little Ice Age (LIA). Allelic frequency changes were assessed from whole-genome pooled sequences for four age-structured cohorts of sessile oak (Quercus petraea) dating back to 1680, in each of three different oak forests in France. The genetic covariances of allelic frequency changes increased between successive time periods, highlighting genome-wide effects of linked selection. We found imprints of parallel linked selection in the three forests during the late LIA, and a shift of selection during more recent time periods of the Anthropocene. The changes in allelic covariances within and between forests mirrored the documented changes in the occurrence of extreme events (droughts and frosts) over the last 300 years. The genomic regions with the highest covariances were enriched in genes involved in plant responses to pathogens and abiotic stresses (temperature and drought). These responses are consistent with the reported sequence of frost (or drought) and disease damage ultimately leading to the oak dieback after extreme events. They provide support for adaptive evolution of long-lived species during recent climatic changes. Although we acknowledge that other sources (e.g., gene flow, generation overlap) may have contributed to temporal covariances of allelic frequency changes, the consistent and correlated response across the three forests lends support to the existence of a systematic driving force such as natural selection.
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30.
  • Segami, Julia Carolina, et al. (författare)
  • Should females prefer old males?
  • 2021
  • Ingår i: Evolution Letters. - : John Wiley & Sons. - 2056-3744. ; 5:5, s. 507-520
  • Tidskriftsartikel (refereegranskat)abstract
    • Whether females should prefer to mate with old males is controversial. Old males may sire offspring of low quality because of an aging germline, but their proven ability to reach an old age can also be an excellent indicator of superior genetic quality, especially in natural populations. These genetic effects are, however, hard to study in nature, because they are often confounded with direct benefits offered by old males to the female, such as experience and high territory quality. We, therefore, used naturally occurring extra-pair young to disentangle different aspects of male age on female fitness in a natural population of collared flycatchers because any difference between within- and extra-pair young within a nest should be caused by paternal genetic effects only. Based on 18 years of long-term data, we found that females paired with older males as social partners experienced an overall reproductive advantage. However, offspring sired by old males were of lower quality as compared to their extra-pair half-siblings, whereas the opposite was found in nests attended by young males. These results imply a negative genetic effect of old paternal age, given that extra-pair males are competitive middle-age males. Thus, offspring may benefit from being sired by young males but raised by old males, to maximize both genetic and direct effects. Our results show that direct and genetic benefits from pairing with old males may act in opposing directions and that the quality of the germline may deteriorate before other signs of senescence become obvious.
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31.
  • Svensson, Erik I., et al. (författare)
  • Heritable variation in thermal profiles is associated with reproductive success in the world's largest bird
  • 2024
  • Ingår i: Evolution letters. - 2056-3744. ; 8:2, s. 200-211
  • Tidskriftsartikel (refereegranskat)abstract
    • Organisms inhabiting extreme thermal environments, such as desert birds, have evolved spectacular adaptations to thermoregulate during hot and cold conditions. However, our knowledge of selection for thermoregulation and the potential for evolutionary responses is limited, particularly for large organisms experiencing extreme temperature fluctuations. Here we use thermal imaging to quantify selection and genetic variation in thermoregulation in ostriches (Struthio camelus), the world's largest bird species that is experiencing increasingly volatile temperatures. We found that females who are better at regulating their head temperatures (“thermoregulatory capacity”) had higher egg-laying rates under hotter conditions. Thermoregulatory capacity was both heritable and showed signatures of local adaptation: females originating from more unpredictable climates were better at regulating their head temperatures in response to temperature fluctuations. Together these results reveal that past and present evolutionary processes have shaped genetic variation in thermoregulatory capacity, which appears to protect critical organs, such as the brain, from extreme temperatures during reproduction.
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32.
  • Thorley, Jack, et al. (författare)
  • Damaraland mole-rats do not rely on helpers for reproduction or survival
  • 2023
  • Ingår i: Evolution Letters. - : Oxford University Press. - 2056-3744. ; 7:4, s. 203-215
  • Tidskriftsartikel (refereegranskat)abstract
    • In eusocial invertebrates and obligate cooperative breeders, successful reproduction is dependent on assistance from non-breeding group members. Although naked (Heterocephalus glaber) and Damaraland mole-rats (Fukomys damarensis) are often described as eusocial and their groups are suggested to resemble those of eusocial insects more closely than groups of any other vertebrate, the extent to which breeding individuals benefit from the assistance of non-breeding group members is unclear. Here we show that, in wild Damaraland mole-rats, prospective female breeders usually disperse and settle alone in new burrow systems where they show high survival rates and remain in good body condition-often for several years-before being joined by males. In contrast to many obligate cooperative vertebrates, pairs reproduced successfully without non-breeding helpers, and the breeding success of experimentally formed pairs was similar to that of larger, established groups. Though larger breeding groups recruited slightly more pups than smaller groups, adult survival was independent of group size and group size had mixed effects on the growth of non-breeders. Our results suggest that Damaraland mole-rats do not need groups to survive and that cooperative breeding in the species is not obligate as pairs can-and frequently do-reproduce without the assistance of helpers. While re-emphasizing the importance of ecological constraints on dispersal in social mole-rats, the mixed effects of group size in our study suggest that indirect benefits accrued through cooperative behavior may have played a less prominent role in the evolution of mole-rat group-living than previously thought. Lay Summary Social mole-rats are subterranean rodents that live in family groups where a single breeding female is responsible for the production of all pups. It has frequently been suggested that her non-breeding offspring act as helpers and increase the survival of all group members through cooperative foraging, which is thought to increase the rate at which tubers and other geophytes-the principal food of mole-rats-are found. Such helper effects are expected to generate positive associations between group size and reproduction, growth, and survival, but have rarely been looked for in wild populations. After monitoring a population of Damaraland mole-rats in the Southern Kalahari over 7 years, we found that the effect of non-breeders on the reproductive output of breeding females was modest: large groups recruited only slightly more offspring than smaller groups, and the experimental creation of breeding pairs showed that newly formed groups can start breeding immediately and reproduce at rates comparable to established groups. Effects of group size on individual growth rates and on individual survival were also limited, with solitary females in particular-females who have dispersed from their natal group and settled alone-showing high survival rates that approached that of breeding females. Taken together, our results suggests that the extent to which breeding females rely on non-breeders as helpers in mole-rat societies may be less pronounced than previously thought. Helper effects appear relatively weak and the principal reason that offspring delay dispersal is likely because of the strong constraints on dispersal in this species.
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33.
  • Urban, Mark C., et al. (författare)
  • When and how can we predict adaptive responses to climate change?
  • 2024
  • Ingår i: Evolution Letters. - : Oxford University Press. - 2056-3744. ; 8:1, s. 172-187
  • Tidskriftsartikel (refereegranskat)abstract
    • Predicting if, when, and how populations can adapt to climate change constitutes one of the greatest challenges in science today. Here, we build from contributions to the special issue on evolutionary adaptation to climate change, a survey of its authors, and recent literature to explore the limits and opportunities for predicting adaptive responses to climate change. We outline what might be predictable now, in the future, and perhaps never even with our best efforts. More accurate predictions are expected for traits characterized by a well-understood mapping between genotypes and phenotypes and traits experiencing strong, direct selection due to climate change. A meta-analysis revealed an overall moderate trait heritability and evolvability in studies performed under future climate conditions but indicated no significant change between current and future climate conditions, suggesting neither more nor less genetic variation for adapting to future climates. Predicting population persistence and evolutionary rescue remains uncertain, especially for the many species without sufficient ecological data. Still, when polled, authors contributing to this special issue were relatively optimistic about our ability to predict future evolutionary responses to climate change. Predictions will improve as we expand efforts to understand diverse organisms, their ecology, and their adaptive potential. Advancements in functional genomic resources, especially their extension to non-model species and the union of evolutionary experiments and "omics," should also enhance predictions. Although predicting evolutionary responses to climate change remains challenging, even small advances will reduce the substantial uncertainties surrounding future evolutionary responses to climate change. Preventing biological impacts from climate change will require accurate predictions about which species and ecosystems are most at risk and how best to protect them. Despite some progress, most predictive efforts still omit the potential for evolution to mediate climate change impacts. Here, we evaluate what is predictable now, in the future, and likely never based on recent literature, a survey of authors, and authors' contributions to a special issue on climate change evolution. Evidence indicates a growing ability to predict at least some components underlying evolutionary dynamics. For instance, the direct effects of climate change often alter natural selection regimes that could elicit evolutionary responses assuming sufficient additive genetic variation. We found no evidence for an increase or decrease in evolvability under future climate conditions, but we did find an overall moderate level of evolvability. However, the specific genetics underlying potential adaptive changes are still a "black box" that remains difficult to predict. We not only discuss the opportunities afforded by new genomic techniques to elucidate these genetic black boxes but also caution that the costs and limitations of such techniques for many species might not warrant their general practicality. We highlight further progress and challenges in predicting gene flow and population persistence, both of which can facilitate evolutionary rescue. We finish by listing ten activities that are needed to accelerate future progress in predicting climate change evolution. Despite the many complexities, we are relatively optimistic that evolutionary responses to climate change are becoming more accurate through time, especially assuming a more focused effort to fill key knowledge gaps in the coming years.
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34.
  • Videvall, Elin, et al. (författare)
  • Coprophagy rapidly matures juvenile gut microbiota in a precocial bird
  • 2023
  • Ingår i: Evolution Letters. - : Oxford University Press. - 2056-3744. ; 7:4, s. 240-251
  • Tidskriftsartikel (refereegranskat)abstract
    • Coprophagy is a behavior where animals consume feces, and has been observed across a wide range of species, including birds and mammals. The phenomenon is particularly prevalent in juveniles, but the reasons for this remain unclear. One hypothesis is that coprophagy enables offspring to acquire beneficial gut microbes that aid development. However, despite the potential importance of this behavior, studies investigating the effects in juveniles are rare. Here we experimentally test this idea by examining how ingestion of adult feces by ostrich chicks affects their gut microbiota development, growth, feeding behavior, pathogen abundance, and mortality. We conducted extensive longitudinal experiments for 8 weeks, repeated over 2 years. It involved 240 chicks, of which 128 were provided daily access to fresh fecal material from adults and 112 were simultaneously given a control treatment. Repeated measures, behavioral observations, and DNA metabarcoding of the microbial gut community, both prior to and over the course of the experiment, allowed us to evaluate multiple aspects of the behavior. The results show that coprophagy causes (a) marked shifts to the juvenile gut microbiota, including a major increase in diversity and rapid maturation of the microbial composition, (b) higher growth rates (fecal-supplemented chicks became 9.4% heavier at 8 weeks old), (c) changes to overall feeding behavior but no differences in feed intake, (d) lower abundance of a common gut pathogen (Clostridium colinum), and (e) lower mortality associated with gut disease. Together, our results suggest that the behavior of coprophagy in juveniles is highly beneficial and may have evolved to accelerate the development of gut microbiota.
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35.
  • Walter, Greg M., et al. (författare)
  • Loss of ecologically important genetic variation in late generation hybrids reveals links between adaptation and speciation
  • 2020
  • Ingår i: Evolution Letters. - : JOHN WILEY & SONS LTD. - 2056-3744. ; 4:4, s. 302-316
  • Tidskriftsartikel (refereegranskat)abstract
    • Adaptation to contrasting environments occurs when advantageous alleles accumulate in each population, but it remains largely unknown whether these same advantageous alleles create genetic incompatibilities that can cause intrinsic reproductive isolation leading to speciation. Identifying alleles that underlie both adaptation and reproductive isolation is further complicated by factors such as dominance and genetic interactions among loci, which can affect both processes differently and obscure potential links between adaptation and speciation. Here, we use a combination of field and glasshouse experiments to explore the connection between adaptation and speciation while accounting for dominance and genetic interactions. We created a hybrid population with equal contributions from four contrasting ecotypes ofSenecio lautus(Asteraceae), which produced hybrid genomes both before (F1 hybrid generation) and after (F4 hybrid generation) recombination among the parental ecotypes. In the glasshouse, plants in the second generation (F2 hybrid generation) showed reduced fitness as a loss of fertility. However, fertility was recovered in subsequent generations, suggesting that genetic variation underlying the fitness reduction was lost in subsequent generations. To quantify the effects of losing genetic variation at the F2 generation on the fitness of later generation hybrids, we used a reciprocal transplant to test for fitness differences between parental ecotypes, and F1 and F4 hybrids in all four parental habitats. Compared to the parental ecotypes and F1 hybrids, variance in F4 hybrid fitness was lower, and lowest in habitats that showed stronger native-ecotype advantage, suggesting that stronger natural selection for the native ecotype reduced fitness variation in the F4 hybrids. Fitness trade-offs that were present in the parental ecotypes and F1 hybrids were absent in the F4 hybrid. Together, these results suggest that the genetic variation lost after the F2 generation was likely associated with both adaptation and intrinsic reproductive isolation among ecotypes from contrasting habitats.
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36.
  • Westram, A. M., et al. (författare)
  • Clines on the seashore: The genomic architecture underlying rapid divergence in the face of gene flow
  • 2018
  • Ingår i: Evolution Letters. - : Oxford University Press (OUP). - 2056-3744. ; 2:4, s. 297-309
  • Tidskriftsartikel (refereegranskat)abstract
    • Adaptive divergence and speciation may happen despite opposition by gene flow. Identifying the genomic basis underlying divergence with gene flow is a major task in evolutionary genomics. Most approaches (e.g., outlier scans) focus on genomic regions of high differentiation. However, not all genomic architectures potentially underlying divergence are expected to show extreme differentiation. Here, we develop an approach that combines hybrid zone analysis (i.e., focuses on spatial patterns of allele frequency change) with system-specific simulations to identify loci inconsistent with neutral evolution. We apply this to a genome-wide SNP set from an ideally suited study organism, the intertidal snail Littorina saxatilis, which shows primary divergence between ecotypes associated with different shore habitats. We detect many SNPs with clinal patterns, most of which are consistent with neutrality. Among non-neutral SNPs, most are located within three large putative inversions differentiating ecotypes. Many non-neutral SNPs show relatively low levels of differentiation. We discuss potential reasons for this pattern, including loose linkage to selected variants, polygenic adaptation and a component of balancing selection within populations (which may be expected for inversions). Our work is in line with theory predicting a role for inversions in divergence, and emphasizes that genomic regions contributing to divergence may not always be accessible with methods purely based on allele frequency differences. These conclusions call for approaches that take spatial patterns of allele frequency change into account in other systems.
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37.
  • Wiberg, R. Axel W., et al. (författare)
  • Experimental evolution supports signatures of sexual selection in genomic divergence
  • 2021
  • Ingår i: Evolution Letters. - : Oxford University Press (OUP). - 2056-3744. ; 5:3, s. 214-229
  • Tidskriftsartikel (refereegranskat)abstract
    • Comparative genomics has contributed to the growing evidence that sexual selection is an important component of evolutionary divergence and speciation. Divergence by sexual selection is implicated in faster rates of divergence of the X chromosome and of genes thought to underlie sexually selected traits, including genes that are sex biased in expression. However, accurately inferring the relative importance of complex and interacting forms of natural selection, demography, and neutral processes that occurred in the evolutionary past is challenging. Experimental evolution provides an opportunity to apply controlled treatments for multiple generations and examine the consequent genomic divergence. Here, we altered sexual selection intensity, elevating sexual selection in polyandrous lines and eliminating it in monogamous lines, and examined patterns of allele frequency divergence in the genome of Drosophila pseudoobscura after more than 160 generations of experimental evolution. Divergence is not uniform across the genome but concentrated in islands, many of which contain candidate genes implicated in mating behaviors and other sexually selected phenotypes. These are more often seen on the X chromosome, which also shows greater divergence in F-ST than neutral expectations. There are characteristic signatures of selection seen in these regions, with lower diversity on the X chromosome than the autosomes, and differences in diversity on the autosomes between selection regimes. Reduced Tajima's D within some of the divergent regions may imply that selective sweeps have occurred, despite considerable recombination. These changes are associated with both differential gene expression between the lines and sex-biased gene expression within the lines. Our results are very similar to those thought to implicate sexual selection in divergence between species and natural populations, and hence provide experimental support for the likely role of sexual selection in driving such types of genetic divergence, but also illustrate how variable outcomes can be for different genomic regions.
  •  
38.
  • Wielstra, Ben, et al. (författare)
  • A genomic footprint of hybrid zone movement in crested newts.
  • 2017
  • Ingår i: Evolution letters. - : Oxford University Press (OUP). - 2056-3744. ; 1:2, s. 93-101
  • Tidskriftsartikel (refereegranskat)abstract
    • Speciation typically involves a stage in which species can still exchange genetic material. Interspecific gene flow is facilitated by the hybrid zones that such species establish upon secondary contact. If one member of a hybridizing species pair displaces the other, their hybrid zone would move across the landscape. Although theory predicts that moving hybrid zones quickly stagnate, hybrid zones tracked over one or a few decades do not always follow such a limitation. This suggests that hybrid zones have the potential to traverse considerable distances over extended periods of time. When hybrid zones move, introgression is predicted to result in biased gene flow of selectively neutral alleles, from the receding species into the advancing species. We test for such a genomic footprint of hybrid zone movement in a pair of crested newt species (genus Triturus) for which we have a priori support for westward hybrid zone movement. We perform a multilocus phylogeographical survey and conduct Bayesian clustering analysis, estimation of ancestry and heterozygosity, and geographical cline analysis. In a 600 km wide area east of the present day hybrid zone a genomic footprint constitutes empirical evidence consistent with westward hybrid zone movement. The crested newt case suggests that hybrid zone movement can occur over an extensive span of time and space. Inferring hybrid zone movement provides fundamental insight into historical biogeography and the speciation process, and we anticipate that hybrid zones will prove to be far more mobile than currently appreciated.
  •  
39.
  • Wright, Alison E., et al. (författare)
  • Male-biased gene expression resolves sexual conflict through the evolution of sex-specific genetic architecture
  • 2018
  • Ingår i: Evolution Letters. - : Oxford University Press (OUP). - 2056-3744. ; 2:2, s. 52-61
  • Tidskriftsartikel (refereegranskat)abstract
    • Many genes are subject to contradictory selection pressures in males and females, and balancing selection resulting from sexual conflict has the potential to substantially increase standing genetic diversity in populations and thereby act as an important force in adaptation. However, the underlying causes of sexual conflict, and the potential for resolution, remains hotly debated. Using transcriptome-resequencing data from male and female guppies, we use a novel approach, combining patterns of genetic diversity and intersexual divergence in allele frequency, to distinguish the different scenarios that give rise to sexual conflict, and how this conflict may be resolved through regulatory evolution. We show that reproductive fitness is the main source of sexual conflict, and this is resolved via the evolution of male-biased expression. Furthermore, resolution of sexual conflict produces significant differences in genetic architecture between males and females, which in turn lead to specific alleles influencing sex-specific viability. Together, our findings suggest an important role for sexual conflict in shaping broad patterns of genome diversity, and show that regulatory evolution is a rapid and efficient route to the resolution of conflict.
  •  
40.
  • Öhlund, Gunnar, 1977-, et al. (författare)
  • Ecological speciation in European whitefish is driven by a large‐gaped predator
  • 2020
  • Ingår i: Evolution Letters. - : John Wiley & Sons. - 2056-3744. ; 4:3, s. 243-256
  • Tidskriftsartikel (refereegranskat)abstract
    • Lake‐dwelling fish that form species pairs/flocks characterized by body size divergence are important model systems for speciation research. Although several sources of divergent selection have been identified in these systems, their importance for driving the speciation process remains elusive. A major problem is that in retrospect, we cannot distinguish selection pressures that initiated divergence from those acting later in the process. To address this issue, we studied the initial stages of speciation in European whitefish (Coregonus lavaretus) using data from 358 populations of varying age (26–10,000 years). We find that whitefish speciation is driven by a large‐growing predator, the northern pike (Esox lucius). Pike initiates divergence by causing a largely plastic differentiation into benthic giants and pelagic dwarfs: ecotypes that will subsequently develop partial reproductive isolation and heritable differences in gill raker number. Using an eco‐evolutionary model, we demonstrate how pike's habitat specificity and large gape size are critical for imposing a between‐habitat trade‐off, causing prey to mature in a safer place or at a safer size. Thereby, we propose a novel mechanism for how predators may cause dwarf/giant speciation in lake‐dwelling fish species.
  •  
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