| 1. |
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| 2. |
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| 3. |
- Aunapuu, Maano, et al.
(författare)
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Spatial patterns and dynamic responses of arctic food webs corroborate the exploitation ecosystems hypothesis (EEH)
- 2008
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 171:2, s. 249-262
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Tidskriftsartikel (refereegranskat)abstract
- According to the exploitation ecosystems hypothesis (EEH), productive terrestrial ecosystems are characterized by community‐level trophic cascades, whereas unproductive ecosystems harbor food‐limited grazers, which regulate community‐level plant biomass. We tested this hypothesis along arctic‐alpine productivity gradients at the Joatka field base, Finnmark, Norway. In unproductive habitats, mammalian predators were absent and plant biomass was constant, whereas herbivore biomass varied, reflecting the productivity of the habitat. In productive habitats, predatory mammals were persistently present and plant biomass varied in space, but herbivore biomass did not. Plant biomass of productive tundra scrublands declined by 40% when vegetation blocks were transferred to predation‐free islands. Corresponding transfer to herbivore‐free islands triggered an increase in plant biomass. Fertilization of an unproductive tundra heath resulted in a fourfold increase in rodent density and a corresponding increase in winter grazing activity, whereas the total aboveground plant biomass remained unchanged. These results corroborate the predictions of the EEH, implying that the endotherm community and the vegetation of the North European tundra behaves dynamically as if each trophic level consisted of a single population, in spite of local co‐occurrence of >20 plant species representing different major taxonomic groups, growth forms, and defensive strategies.
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| 4. |
- Berglund, Helena, et al.
(författare)
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Endemism Predicts Intrinsic Vulnerability to Nonindigenous Species on Islands.
- 2009
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 174:1, s. 94-101
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: While numerous efforts have been made to identify and quantify factors controlling invasibility of biological communities, less attention has been given to analyzing the expressions of vulnerability to nonindigenous species (NIS). Using the International Union for the Conservation of Nature and Natural Resources Red List database for birds, mammals, and amphibians and the Invasive Species Specialist Group global invasive species database as sources of information, we developed a new indicator for the relative intrinsic vulnerability of islands to NIS. It was calculated from the residuals to the global relationship between the impact of NIS and their exposure to the islands. The impact of NIS was expressed as the proportion of indigenous species threatened by NIS, and the exposure was the number of invasive NIS per number of native species. The residuals corresponded to the variability in impact, about 60%, that was not explained by exposure. The proportion of endemic species on the islands was positively correlated with the relative intrinsic vulnerability and explained about 60% of its variability. The robust relationship between endemism and intrinsic vulnerability reinforces the role of long-term isolation for the fate of island indigenous species to biological invasions and is useful in identifying vulnerable environments without having a specific invader in mind.
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| 5. |
- Brommer, J.E., et al.
(författare)
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Exploring the genetics of aging in a wild passerine bird
- 2007
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 170:4, s. 643-650
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Tidskriftsartikel (refereegranskat)abstract
- Senescence is the decline in survival and reproduction as an organism ages and is known to occur in collared flycatchers Ficedula albicollis. We consider annual fitness (the estimated genetic contribution that an individual makes to next year’s gene pool) as a measure of age‐specific fitness. We apply a restricted maximum likelihood linear mixed‐model approach on 25 years of data on 3,844 male and 4,992 female collared flycatchers. Annual fitness had a significant additive genetic component (h2 of about 4%). Annual fitness declined at later ages in both sexes. Using a random regression animal model, we show that the observed age‐related phenotypic changes in annual fitness were not present on the additive genetic level, contrary to predictions of genetic hypotheses of senescence. Our study suggests that patterns of aging in the wild need to be interpreted with caution in terms of underlying genetics because they may be largely determined by environmental processes.
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| 6. |
- Cherif, Mehdi, et al.
(författare)
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Stoichiometric constraints on resource use, competitive interactions, and elemental cycling in microbial decomposers
- 2007
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Ingår i: American Naturalist. - McGill Univ, Dept Biol, Montreal, PQ H3A 1B1, Canada. Ecole Normale Super, Biogeochim & Ecol Milieux Continentaux Lab, UMR 7618, F-75230 Paris 05, France. : UNIV CHICAGO PRESS. - 0003-0147 .- 1537-5323. ; 169:6, s. 709-724
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Tidskriftsartikel (refereegranskat)abstract
- Heterotrophic microbial decomposers, such as bacteria and fungi, immobilize or mineralize inorganic elements, depending on their elemental composition and that of their organic resource. This fact has major implications for their interactions with other consumers of inorganic elements. We combine the stoichiometric and resource-ratio approaches in a model describing the use by decomposers of an organic and an inorganic resource containing the same essential element, to study its consequences on decomposer interactions and their role in elemental cycling. Our model considers the elemental composition of organic matter and the principle of its homeostasis explicitly. New predictions emerge, in particular, ( 1) stoichiometric constraints generate a trade-off between the R* values of decomposers for the two resources; ( 2) they create favorable conditions for the coexistence of decomposers limited by different resources and with different elemental demands; ( 3) however, combined with conditions on species-specific equilibrium limitation, they draw decomposers toward colimitation by the organic and inorganic resources on an evolutionary time scale. Moreover, we derive the conditions under which decomposers switch from consumption to excretion of the inorganic resource. We expect our predictions to be useful in explaining the community structure of decomposers and their interactions with other consumers of inorganic resources, particularly primary producers.
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| 7. |
- Claessen, David, et al.
(författare)
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The effect of population size and recombination on delayed evolution of polymorphism and speciation in sexual populations
- 2008
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 172:1, s. E18-34
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Tidskriftsartikel (refereegranskat)abstract
- Recent theory suggests that absolute population size may qualitatively influence the outcome of evolution under disruptive selection in asexual populations. Large populations are predicted to undergo rapid evolutionary branching; however, in small populations, the waiting time to branching increases steeply with decreasing abundance, and below a critical size, the population remains monomorphic indefinitely. Here, we (1) extend the theory to sexual populations and (2) confront its predictions with empirical data, testing statistically whether lake size affects the level of resource polymorphism in arctic char (Salvelinus alpinus) in 22 lakes of different sizes. For a given level of recombination, our model predicts qualitatively similar relations between population size and time to evolutionary branching (either speciation or evolution of genetic polymorphism) as the asexual model, while recombination further increases the delay to branching. The loss of polymorphism at certain loci, an inherent aspect of multilocus-trait evolution, may increase the delay to speciation, resulting in stable genetic polymorphism without speciation. The empirical analysis demonstrates that the occurrence of resource polymorphism depends on both lake size and the number of coexisting fish species. For a given number of coexisting species, the level of polymorphism increases significantly with lake size, thus confirming our model prediction.
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| 8. |
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| 9. |
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| 10. |
- Eklöv, Peter, et al.
(författare)
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Predation risk influences adaptive morphological variation in fish populations
- 2006
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 167:3, s. 440-452
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Tidskriftsartikel (refereegranskat)abstract
- Predators can cause a shift in both density and frequency of a prey phenotype that may lead to phenotypic divergence through natural selection. What is less investigated is that predators have a variety of indirect effects on prey that could potentially have large evolutionary responses. We conducted a pond experiment to test whether differences in predation risk in different habitats caused shifts in behavior of prey that, in turn, would affect their morphology. We also tested whether the experimental data could explain the morphological variation of perch in the natural environment. In the experiment, predators caused the prey fish to shift to the habitat with the lower predation risk. The prey specialized on habitat-specific resources, and there was a strong correlation between diet of the prey fish and morphological variation, suggesting that resource specialization ultimately affected the morphology. The lack of differences in competition and mortality suggest that the morphological variation among prey was induced by differences in predation risk among habitats. The field study demonstrated that there are differences in growth related to morphology of perch in two different habitats. Thus, a trade-off between foraging and predator avoidance could be responsible for adaptive morphological variation of young perch.
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| 11. |
- Gosden, Thomas, et al.
(författare)
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Density-dependent male mating harassment, female resistance, and male mimicry.
- 2009
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 173:6, s. 709-721
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Tidskriftsartikel (refereegranskat)abstract
- Genetic variation in female resistance and tolerance to male mating harassment can affect the outcome of sexually antagonistic mating interactions. We investigated female mating rates and male mating harassment in natural populations of a damselfly (Ischnura elegans). This damselfly species has a heritable sex-limited polymorphism in females, where one of the morphs is a male mimic (androchrome females). The three female morphs differ in mating rates, and these differences are stable across populations and years. However, the degree of premating resistance toward male mating attempts varied across generations and populations. Male mating harassment of the female morphs changed in a density-dependent fashion, suggesting that male mate preferences are plastic and vary with the different morph densities. We quantified morph differences in male mating harassment and female fecundity, using path analysis and structural equation modeling. We found variation between the morphs in the fitness consequences of mating, with the fecundity of one of the nonmimetic morphs declining with increasing male mating harassment. However, androchrome females had lower overall fecundity, presumably reflecting a cost of male mimicry. Density-dependent male mating harassment on the morphs and fecundity costs of male mimicry are thus likely to contribute to the maintenance of this female polymorphism.
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| 12. |
- Gossner, Martin M., et al.
(författare)
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Native Fauna on Exotic Trees : Phylogenetic Conservatism and Geographic Contingency in Two Lineages of Phytophages on Two Lineages of Trees
- 2009
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 173:5, s. 599-614
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Tidskriftsartikel (refereegranskat)abstract
- The relative roles of evolutionary history and geographical and ecological contingency for community assembly remain unknown. Plant species, for instance, share more phytophages with closer relatives (phylogenetic conservatism), but for exotic plants introduced to another continent, this may be overlaid by geographically contingent evolution or immigration from locally abundant plant species (mass effects). We assessed within local forests to what extent exotic trees (Douglas-fir, red oak) recruit phytophages (Coleoptera, Heteroptera) from more closely or more distantly related native plants. We found that exotics shared more phytophages with natives from the same major plant lineage (angiosperms vs. gymnosperms) than with natives from the other lineage. This was particularly true for Heteroptera, and it emphasizes the role of host specialization in phylogenetic conservatism of host use. However, for Coleoptera on Douglas-fir, mass effects were important: immigration from beech increased with increasing beech abundance. Within a plant phylum, phylogenetic proximity of exotics and natives increased phytophage similarity, primarily in younger Coleoptera clades on angiosperms, emphasizing a role of past codiversification of hosts and phytophages. Overall, phylogenetic conservatism can shape the assembly of local phytophage communities on exotic trees. Whether it outweighs geographic contingency and mass effects depends on the interplay of phylogenetic scale, local abundance of native tree species, and the biology and evolutionary history of the phytophage taxon.
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| 13. |
- Harding, Karin C., 1968, et al.
(författare)
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Acquired immunity and stochasticity in epidemic intervals impede the evolution of host disease resistance
- 2005
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 166:6, s. 722-730
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Tidskriftsartikel (refereegranskat)abstract
- Disease can generate intense selection pressure on host populations, but here we show that acquired immunity in a population subject to repeated disease outbreaks can impede the evolution of genetic disease resistance by maintaining susceptible genotypes in the population. Interference between the life-history schedule of a species and periodicity of the disease has unintuitive effects on selection intensity, and stochasticity in outbreak period further reduces the rate of spread of disease-resistance alleles. A general age-structured population genetic model was developed and parameterized using empirical data for phocine distemper virus (PDV) epizootics in harbor seals. Scenarios with acquired immunity had lower levels of epizootic mortality compared with scenarios without acquired immunity for the first PDV outbreaks, but this pattern was reversed after about five disease cycles. Without acquired immunity, evolution of disease resistance was more rapid, and long-term population size variation is efficiently dampened. Acquired immunity has the potential to significantly influence rapid evolutionary dynamics of a host population in response to age-structured disease selection and to alter predicted selection intensities compared with epidemiological models that do not consider such feedback. This may have important implications for evolutionary population dynamics in a range of human, agricultural, and wildlife disease settings.
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| 14. |
- Hastad, Olle, et al.
(författare)
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Different ranking of avian colors predicted by modeling of retinal function in humans and birds
- 2008
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 171:6, s. 831-838
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Tidskriftsartikel (refereegranskat)abstract
- Only during the past decade have vision-system-neutral methods become common practice in studies of animal color signals. Consequently, much of the current knowledge on sexual selection is based directly or indirectly on human vision, which may or may not emphasize spectral information in a signal differently from the intended receiver. In an attempt to quantify this discrepancy, we used retinal models to test whether human and bird vision rank plumage colors similarly. Of 67 species, human and bird models disagreed in 26 as to which pair of patches in the plumage provides the strongest color contrast or which male in a random pair is the more colorful. These results were only partly attributable to human UV blindness. Despite confirming a strong correlation between avian and human color discrimination, we conclude that a significant proportion of the information in avian visual signals may be lost in translation.
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| 15. |
- Härdling, Roger, et al.
(författare)
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Male mating constraints affect mutual mate choice: prudent male courting and sperm-limited females.
- 2008
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 172:2, s. 259-271
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Tidskriftsartikel (refereegranskat)abstract
- Costs of sperm production may lead to prudence in male sperm allocation and also to male mate choice. Here, we develop a life history-based mutual mate choice model that takes into account the lost-opportunity costs for males from time out in sperm recovery and lets mate competition be determined by the prevailing mate choice strategies. We assume that high mating rate may potentially lead to sperm depletion in males, and that as a result, female reproduction may be limited by the availability of sperm. Increasing variation in male quality leads, in general, to increased selective mate choice by females, and vice versa. Lower-quality males may, however, gain access to more fecund higher-quality females by lowering their courting rate, thus increasing their sperm reserves. When faced with strong male competition for mates, low-quality males become less choosy, which leads to assortative mating for quality and an increased mating rate across all males. With assortative mating, the frequency of antagonistic interactions (sexual conflict) is reduced, allowing males to lower the time spent replenishing sperm reserves in order to increase mating rate. This in turn leads to lower sperm levels at mating and therefore could lead to negative effects on female fitness via sperm limitation.
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| 16. |
- Härdling, Roger, et al.
(författare)
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Nonrandom mating preserves intrasexual polymorphism and stops population differentiation in sexual conflict
- 2006
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 167:3, s. 401-409
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Tidskriftsartikel (refereegranskat)abstract
- Evolutionary conflict between the sexes is predicted to lead to sexual arms races in which male adaptations for acquiring mates (" offense" traits) are met by female counteradaptations - for example, to reduce mating rate (" defense" traits). Such coevolutionary chases may be perpetual. However, we show here that the coevolutionary process may also lead to a stable state in which multiple offense- defense trait pairs are maintained. This type of polymorphism below the species level is a result of sexual conflict in combination with nonrandom mating. Our results show that if nonrandom mating occurs with respect to male and female conflict traits, genetic correlations will act to stabilize the trait frequencies so that all morphs are maintained. We discuss the results in special relation to the evolution of female polymorphism in diving beetles and argue that the process we describe may be a general force that maintains polymorphism in other taxa as well.
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| 17. |
- Johansson, Jacob, et al.
(författare)
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Will sympatric speciation fail due to stochastic competitive exclusion?
- 2006
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 168:4, s. 572-578
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Tidskriftsartikel (refereegranskat)abstract
- Sympatric speciation requires coexistence of the newly formed species. If divergence proceeds by small mutational steps, the new species utilize almost the same resources initially, and full speciation may be impeded by competitive exclusion in stochastic environments. We investigate this primarily ecological problem of sympatric speciation by studying the population dynamics of a diverging asexual population in a fluctuating environment. Correlation between species responses to environmental fluctuation is assumed to decrease with distance in trait space. Rapidly declining correlation in combination with high environmental variability may delay full speciation or even render it impossible. Stochastic extinctions impeding speciation are most likely when correlation decays faster than competition, for example, when demographic stochasticity is strong or when divergence is not accompanied by niche separation, such as in speciation driven entirely by sexual selection. Our general theoretical results show an interesting connection between short-term ecological dynamics and long-term, large-scale evolution.
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| 18. |
- Johnston, M. O., et al.
(författare)
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Correlations among fertility components can maintain mixed mating in plants
- 2009
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Ingår i: American Naturalist. - 0003-0147 .- 1537-5323. ; 173:1, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- Classical models studying the evolution of self-fertilization in plants conclude that only complete selfing and complete outcrossing are evolutionarily stable. In contrast with this prediction, 42% of seed-plant species are reported to have rates of self-fertilization between 0.2 and 0.8. We propose that many previous models fail to predict intermediate selfing rates because they do not allow for functional relationships among three components of reproductive fitness: self-fertilized ovules, outcrossed ovules, and ovules sired by successful pollen export. Because the optimal design for fertility components may differ, conflicts among the alternative pathways to fitness are possible, and the greatest fertility may be achieved with some self-fertilization. Here we develop and analyze a model to predict optimal selfing rates that includes a range of possible relationships among the three components of reproductive fitness, as well as the effects of evolving inbreeding depression caused by deleterious mutations and of selection on total seed number. We demonstrate that intermediate selfing is optimal for a wide variety of relationships among fitness components and that inbreeding depression is not a good predictor of selfing-rate evolution. Functional relationships subsume the myriad effects of individual plant traits and thus offer a more general and simpler perspective on mating system evolution.
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| 19. |
- Ketterson, E D, et al.
(författare)
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Testosterone in females: Mediator of adaptive traits, constraint on sexual dimorphism, or both?
- 2005
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 166:4, s. 85-98
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Tidskriftsartikel (refereegranskat)abstract
- When selection on males and females differs, the sexes may diverge in phenotype. Hormones serve as a proximate regulator of sex differences by mediating sex-biased trait expression. To integrate these perspectives, we consider how suites of traits mediated by the same hormone in both sexes might respond to selection. In male birds, plasma testosterone (T) varies seasonally and among species according to mating system. When elevated experimentally, it is known to enhance some components of fitness and to decrease others. We report that female T also varies seasonally and co-varies with male T. Female T is higher in relation to male T in sexually monomorphic species and is higher absolutely in females of species with socially monogamous mating systems, which suggests adaptation. We also consider the effect of experimentally elevated T on females and whether traits are sensitive to altered T. We hypothesize that sensitive traits could become subject to selection after a natural change in T and that traits with opposing fitness consequences in males and females could constrain dimorphism. Results from birds, including the dark-eyed junco (Junco hyemalis), reveal many sensitive traits, some of which appear costly and may help to account for observed levels of sexual dimorphism.
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| 20. |
- Kurtz, Joachim, et al.
(författare)
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An experimental test of the immunocompetence handicap hypothesis in a teleost fish: 11-ketotestosterone suppresses innate immunity in three-spined sticklebacks
- 2007
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 170:4, s. 509-519
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Tidskriftsartikel (refereegranskat)abstract
- The immunocompetence handicap hypothesis (ICHH) provides a functional explanation for how sexual ornaments can provide honest signals of male quality. A key aspect of this hypothesis is that testosterone (T) has a bimodal effect: a higher T level enhances the expression of ornaments (increasing mating success and, ultimately, fitness); however, at the same time, it suppresses immune function. Tests of the latter assumption, which have focused mainly on aspects of adaptive immunity in birds, led to equivocal results. We performed a hormone‐implant experiment in male three‐spined sticklebacks (Gasterosteus aculeatus) to test the key assumptions of the ICHH in a fish, where the dominant circulating androgen is 11‐ketotestosterone (11kT) rather than T. Males were implanted with 11‐ketoandrostenedione, which is a natural precursor of 11kT. Each individual's circulating 11kT level, ornamentation, and immunocompetence were measured 2 weeks later. In addition, we quantified oxidative tissue damage because the ICHH has been hypothesized to work via oxidative stress. We found that the males' 11kT levels correlated positively with ornamentation but negatively with immunocompetence, in particular, measures of innate immunity. Moreover, there was a trend for fish with high 11kT levels to suffer more from oxidative stress. Thus, our data provide support for the ICHH.
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| 21. |
- Lankinen, Åsa, et al.
(författare)
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Pollen donor identity affects timing of stigma receptivity in Collinsia heterophylla (Plantaginaceae): a sexual conflict during pollen competition?
- 2007
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 170, s. 854-863
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Tidskriftsartikel (refereegranskat)abstract
- Theory predicts that, during pollen competition, selection may favor a pollen trait that increases donor competitive ability at the expense of the female reproductive function. One such pollen trait could be manipulation of the onset of stigma receptivity. We evaluated the potential occurrence of this kind of sexual conflict by testing female control of the timing of stigma receptivity in the self-compatible annual Collinsia heterophylla. By performing one-donor crosses in the greenhouse, we found that differences in both recipients and pollen donors influenced when stigmas became receptive. Because we did not detect an interaction effect, our result suggests that some donors were consistently better than others at germinating pollen and siring seeds earlier. Unexpectedly, self-pollen was able to fertilize seeds earlier during floral development compared with outcross pollen. These results suggest that female control on timing of stigma receptivity is not complete in this species. In addition, fertilizations that occurred early during floral development resulted in fewer seeds than later fertilizations, possibly indicating a cost of lost control over the onset of receptivity. The ability of pollen donors to influence the timing of stigma receptivity might reflect a conflict between the sexual functions in C. heterophylla.
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| 22. |
- Lovlie, Hanne, et al.
(författare)
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Sex in the morning or in the evening? : Females adjust daily mating patterns to the intensity of sexual harassment
- 2007
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 170:1, s. E1-E13
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Tidskriftsartikel (refereegranskat)abstract
- Selection on males to mate at a higher rate than females often results in male harassment of females and counteracting female responses. When the reproductive value of copulation changes over time, these mating strategies are expected to be time dependent. Here, we demonstrate that variation in the intensity of male harassment leads to drastic changes in female daily mating patterns. In feral populations of fowl Gallus gallus domesticus, male harassment is intense, particularly in the evening when inseminations are most likely to result in fertilization. We experimentally manipulated the intensity of male harassment through similar‐sized groups of different sex ratios. Male mating propensity was always higher than females’, particularly in male‐biased groups and in the evening, when males were closer to and more likely to approach females. Females counteracted male harassment by escalating resistance to mating and—crucially—by shifting their daily mating pattern: in strongly female‐biased groups with relaxed sexual harassment, females solicited sex in the evening, while in male‐biased groups, they solicited sex in the morning, thus avoiding harassment in the evening. Together, these results indicate that intersexual conflict may occur not only over mating rates but also over when in the day to copulate.
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| 23. |
- Mank, Judith E, et al.
(författare)
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Pleiotropic constraint hampers the resolution of sexual antagonism in vertebrate gene expression
- 2008
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 171:1, s. 35-43
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Tidskriftsartikel (refereegranskat)abstract
- The numerous physiological and phenotypic differences between the sexes, as well as the disparity between male and female reproductive interests, result in sexual conflicts, which are often manifested at the genomic level. Sexually antagonistic genes benefit one sex at the expense of the other and experience strong pressure to evolve male- and female-specific expression patterns to resolve sexual conflicts and maximize fitness for both sexes. Sex-biased gene expression has recently been demonstrated for much of the metazoan transcriptome, suggesting that many loci are sexually antagonistic. However, many coding regions function in multiple processes throughout the organism. This pleiotropy increases the complexity of selection for any given gene, which in turn may obscure sex-specific selective pressures and hamper the evolution of sex-biased gene expression. Here we use microarray gene expression data, in conjunction with data on transcript abundance from expressed sequence tag libraries, to demonstrate that loci with sex-biased gene expression are significantly less pleiotropic than unbiased genes. This relationship was independent of sex chromosome gene dosage effects, and the results were concordant across two study organisms, chicken and mouse. These results suggest that the resolution of sexually antagonistic gene expression is determined by the evolutionary constraints acting on any given antagonistic locus.
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| 24. |
- Mank, Judith E.
(författare)
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The evolution of sexually selected traits and antagonistic androgen expression in actinopterygiian fishes
- 2007
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 169:1, s. 142-149
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Tidskriftsartikel (refereegranskat)abstract
- Many sexually selected traits in male fishes are controlled by testosterone. Directional selection for male ornaments could theoretically increase male testosterone levels over evolutionary time-scales, and when genetically correlated, female testosterone levels as well. Because of the negative fitness consequences of high testosterone, it is plausible that female choice for sexually selected traits in males results in decreased female reproductive fitness. I used comparative analysis to examine the association between male peak testosterone expression and sexually selected ornaments. I also tested for genetic correlation between male and female androgen levels. The presence of sexually selected traits in males was significantly correlated with increased peak androgen levels in males as well as females, and female testosterone levels were significantly correlated with male peak testosterone titers, although the slope was only marginally < 1. This suggests that selection to decouple high male and female testosterone levels is either weak or otherwise ineffective.
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| 25. |
- Monroe, Melanie J., 1982-, et al.
(författare)
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Do speciation rates drive rates of body size evolution in mammals?
- 2009
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 174:6, s. 912-918
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Tidskriftsartikel (refereegranskat)abstract
- Recently, it has been shown with large data sets of extinct mammals that large‐bodied lineages experienced higher speciation and extinction rates; with extant mammals, it has been shown that body size evolution is accelerated during speciation. Therefore, it is interesting to investigate whether mammalian body size evolution is faster in large‐bodied lineages. Phylogenetic analysis assuming size‐independent speciation rates suggested that the rate of body size evolution increases with body size, whereas size differences in recent sister species (that are little affected by species turnover) appear to be independent of size. This supports the hypothesis that high rates of species turnover increase the rate at which interspecific differences accumulate in large‐bodied clades, whereas rates of evolution in single lineages are approximately size invariant. Similarly, these findings support the notion that mammalian body size evolution is indeed concentrated in speciation events.
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| 26. |
- Petchey, Owen L., et al.
(författare)
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Trophically Unique Species Are Vulnerable to Cascading Extinction
- 2008
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 171:5, s. 568-579
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Tidskriftsartikel (refereegranskat)abstract
- Understanding which species might become extinct and the consequences of such loss is critical. One consequence is a cascade of further, secondary extinctions. While a significant amount is known about the types of communities and species that suffer secondary extinctions, little is known about the consequences of secondary extinctions for biodiversity. Here we examine the effect of these secondary extinctions on trophic diversity, the range of trophic roles played by the species in a community. Our analyses of natural and model food webs show that secondary extinctions cause loss of trophic diversity greater than that expected from chance, a result that is robust to variation in food web structure, distribution of interactions strengths, functional response, and adaptive foraging. Greater than expected loss of trophic diversity occurs because more trophically unique species are more vulnerable to secondary extinction. This is not a straightforward consequence of these species having few links with others but is a complex function of how direct and indirect interactions affect species persistence. A positive correlation between a species’ extinction probability and the importance of its loss defines high-risk species and should make their conservation a priority.
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| 27. |
- Saether, Stein Are, et al.
(författare)
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Direct and indirect mate choice on leks.
- 2005
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Ingår i: The American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 166, s. 145-157
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Tidskriftsartikel (refereegranskat)
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| 28. |
- Schultz, Stewart T., et al.
(författare)
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Mutation Accumulation in Real Branches : Fitness Assays for Genomic Deleterious Mutation Rate and Effect in Large-Statured Plants
- 2009
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 174:2, s. 163-175
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Tidskriftsartikel (refereegranskat)abstract
- The genomic deleterious mutation rate and mean effect are central to the biology and evolution of all species. Large‐statured plants, such as trees, are predicted to have high mutation rates due to mitotic mutation and the absence of a sheltered germ line, but their size and generation time has hindered genetic study. We develop and test approaches for estimating deleterious mutation rates and effects from viability comparisons within the canopy of large‐statured plants. Our methods, inspired by E. J. Klekowski, are a modification of the classic Bateman‐Mukai mutation‐accumulation experiment. Within a canopy, cell lineages accumulate mitotic mutations independently. Gametes or zygotes produced at more distal points by these cell lineages contain more mitotic mutations than those at basal locations, and within‐flower selfs contain more homozygous mutations than between‐flower selfs. The resulting viability differences allow demonstration of lethal mutation with experiments similar in size to assays of genetic load and allow estimates of the rate and effect of new mutations with moderate precision and bias similar to that of classic mutation‐accumulation experiments in small‐statured organisms. These methods open up new possibilities with the potential to provide valuable new insights into the evolutionary genetics of plants.
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| 29. |
- Stephens, P. A., et al.
(författare)
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The scaling of diving time budgets: Insights from an optimality approach
- 2008
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 171:3, s. 305-314
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Tidskriftsartikel (refereegranskat)abstract
- Simple scaling arguments suggest that, among air-breathing divers, dive duration should scale approximately with mass to the one-third power. Recent phylogenetic analyses appear to confirm this. The same analyses showed that duration of time spent at the surface between dives has scaling very similar to that of dive duration, with the result that the ratio of dive duration to surface pause duration is approximately mass invariant. This finding runs counter to other arguments found in the diving literature that suggest that surface pause duration should scale more positively with mass, leading to a negative scaling of the dive-pause ratio. We use a published model of optimal time allocation in the dive cycle to show that optimal decisions can predict approximate mass invariance in the dive-pause ratio, especially if metabolism scales approximately with mass to the two-thirds power (as indicated by some recent analyses) and oxygen uptake is assumed to have evolved to supply the body tissues at the required rate. However, emergent scaling rules are sensitive to input parameters, especially to the relationship between the scaling of metabolism and oxygen uptake rate at the surface. Our results illustrate the utility of an optimality approach for developing predictions and identifying key areas for empirical research on the allometry of diving behavior.
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| 30. |
- Svanbäck, Richard, et al.
(författare)
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Fluctuating population dynamics promotes the evolution of phenotypic plasticity
- 2009
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 174:2, s. 176-189
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical and empirical studies are showing evidence in support of evolutionary branching and sympatric speciation due to frequency‐dependent competition. However, phenotypic diversification due to underlying genetic diversification is only one possible evolutionary response to disruptive selection. Another potentially general response is phenotypic diversification in the form of phenotypic plasticity. It has been suggested that genetic variation is favored in stable environments, whereas phenotypic plasticity is favored in unstable and fluctuating environments. We investigate the “competition” between the processes of evolutionary branching and the evolution of phenotypic plasticity in a predator‐prey model that allows both processes to occur. In this model, environmental fluctuations can be caused by complicated population dynamics. We found that the evolution of phenotypic plasticity was generally more likely than evolutionary branching when the ecological dynamics exhibited pronounced predator‐prey cycles, whereas the opposite was true when the ecological dynamics was more stable. At intermediate levels of density cycling, trimorphisms with two specialist branches and a phenotypically plastic generalist branch sometimes occurred. Our theoretical results suggest that ecological dynamics and evolutionary dynamics can often be tightly linked and that an explicit consideration of population dynamics may be essential to explain the evolutionary dynamics of diversification in natural populations.
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| 31. |
- Svanbäck, Richard, et al.
(författare)
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Population density fluctuations change the selection gradient in Eurasian perch
- 2009
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 173:4, s. 507-516
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Tidskriftsartikel (refereegranskat)abstract
- A high degree of trophic polymorphism has been associated with the absence of high variability in population density. An explanation for this pattern is that density fluctuations may influence selective regime forms in populations. Still, only few studies have investigated evolutionary dynamics in fluctuating populations. Here we report on a multiyear study of the Eurasian perch, wherein the fitness landscape shifts between stabilizing and directional selection at low density to disruptive selection at high density. Intrinsically driven population fluctuations is the mechanism that most likely explains these shifts in fitness landscape. Stable isotope data showed that the habitat choices of perch were stable over the growing season, indicating that the selection pressure observed each year influenced the fitness of perch in the following year’s reproductive period. Furthermore, the morphological differences between perch caught in the two habitats (littoral and pelagic) were more pronounced at high density than at low density. This study shows that an explicit consideration of population dynamics may be essential to explain the long‐term evolutionary dynamics in populations. In particular, fluctuating population dynamics may be one explanation for why not all polymorphic populations lead to speciation. Instead, fluctuating population dynamics may favor the evolution of phenotypic plasticity.
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| 32. |
- Svensson, Erik, et al.
(författare)
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Female polymorphism, frequency dependence, and rapid evolutionary dynamics in natural populations
- 2005
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 165:5, s. 567-76
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Tidskriftsartikel (refereegranskat)abstract
- Rapid evolutionary change over a few generations has been documented in natural populations. Such changes are observed as organisms invade new environments, and they are often triggered by changed interspecific interactions, such as differences in predation regimes. However, in spite of increased recognition of antagonistic male-female mating interactions, there is very limited evidence that such intraspecific interactions could cause rapid evolutionary dynamics in nature. This is because ecological and longitudinal data from natural populations have been lacking. Here we show that in a color-polymorphic damselfly species, male-female mating interactions lead to rapid evolutionary change in morph frequencies between generations. Field data and computer simulations indicate that these changes are driven by sexual conflict, in which morph fecundities are negatively affected by frequency- and density-dependent male mating harassment. These frequency-dependent processes prevent population divergence by maintaining a female polymorphism in most populations. Although these results contrast with the traditional view of how sexual conflict enhances the rate of population divergence, they are consistent with a recent theoretical model of how females may form discrete genetic clusters in response to male mating harassment.
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| 33. |
- Svensson, Erik, et al.
(författare)
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Selective predation on wing morphology in sympatric damselflies.
- 2007
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Ingår i: American Naturalist. - : University of Chicago Press. - 1537-5323 .- 0003-0147. ; 170:1, s. 101-12
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Tidskriftsartikel (refereegranskat)abstract
- Although predation is thought to affect species divergence, the effects of predator-mediated natural selection on species divergence and in nonadaptive radiations have seldom been studied. Wing melanization in Calopteryx damselflies has important functions in sexual selection and interspecific interactions and in species recognition. The genus Calopteryx and other damselfly genera have also been put forward as examples of radiations driven by sexual selection. We show that avian predation strongly affects natural selection on wing morphology and male wing melanization in two congeneric and sympatric species of this genus (Calopteryx splendens and Calopteryx virgo). Predation risk was almost three times higher for C. virgo, which has an exaggerated degree of wing melanization, than it was for the less exaggerated, sympatric congener C. splendens. Selective predation on the exaggerated species C. virgo favored a reduction and redistribution of the wing melanin patch. There was evidence for nonlinear selection involving wing patch size, wing patch darkness, and wing length and width in C. splendens but weaker nonlinear selection on the same trait combinations in C. virgo. Selective predation could interfere with species divergence by sexual selection and may thus indirectly affect male interspecific interactions, reproductive isolation, and species coexistence in this genus.
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| 34. |
- Tschirren, Barbara, et al.
(författare)
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Heritable Variation in Maternal Yolk Hormone Transfer in a Wild Bird Population
- 2009
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 174:4, s. 557-564
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Tidskriftsartikel (refereegranskat)abstract
- Differential reproductive investment by the mother can critically influence offspring development and phenotype, and strong selection is therefore expected to act on such maternal effects. Although a genetic basis is a prerequisite for phenotypic traits to respond to selection and thus to evolve, we still know very little about the extent of heritable variation in maternal effects in natural populations. Here, we present the first estimates of intrafemale repeatability across breeding seasons and estimates of heritability of hormone-mediated maternal effects in a wild population of collared flycatchers (Ficedula albicollis). We found that maternal yolk testosterone (T) concentrations, yolk mass, and egg mass were moderately to highly repeatable within females across years, whereas intrafemale consistency of maternal yolk androstenedione (A4) deposition was low yet statistically significant. Furthermore, maternal yolk T transfer, yolk mass, and egg mass were significantly heritable, whereas yolk A4 transfer was not. These results strongly suggest that two major maternal yolk androgens are differentially regulated by genes and the environment. Selection on heritable variation in maternal yolk T deposition has the potential to shape the rate and direction of phenotypic change in offspring traits and can thereby accelerate or impede the response to selection in natural populations.
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| 35. |
- Vallejo-Marin, M., et al.
(författare)
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Selection through female fitness helps to explain the maintenance of male flowers
- 2007
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Ingår i: American Naturalist. - 0003-0147 .- 1537-5323. ; 169:5, s. 563-568
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Tidskriftsartikel (refereegranskat)abstract
- Andromonoecy, the production of both male and hermaphrodite flowers in the same individual, is a widespread phenomenon that occurs in approximately 4,000 species distributed in 33 families. Hypotheses for the evolution of andromonoecy suggest that the production of intermediate proportions of staminate flowers may be favored by selection acting through female components of fitness. Here we used the andromonoecious herb Solanum carolinense to determine the pattern of selection on the production of staminate flowers. A multivariate analysis of selection indicates that selection through female fitness favors the production of staminate flowers in at least one population. We conclude that this counterintuitive benefit of staminate flowers on female fitness highlights the importance of considering female components of fitness in the evolution of andromonoecy, a reproductive system usually interpreted as a "male" strategy.
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| 36. |
- Wong, Bob, et al.
(författare)
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Environmental deterioration compromises socially enforced signals of male quality in three-spined sticklebacks
- 2007
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 170:2, s. 184-189
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Tidskriftsartikel (refereegranskat)abstract
- Social costs are often important in promoting the honesty of sexually selected traits. What happens, then, when social costs are relaxed? In species that breed in shallow coastal waters, increases in the frequency and severity of phytoplankton blooms may undermine the value of visual signals by reducing visibility and, in so doing, lead to dishonest signaling by relaxing the social consequences of high signaling effort for poor-quality individuals. Here, we experimentally test the effects of algally induced water turbidity on the role of male-male competition in facilitating reliable sexual displays in three-spined sticklebacks. We found that males in poor condition reduced their courtship effort in the presence of competition in turbid water. This reduction, however, was to a much lesser extent than that observed in clear water. Thus, courtship under conditions of algal turbidity did not reflect male condition as honestly as courtship in clear water. Algal turbidity also influenced breeding coloration, with males in poor condition reducing their area of red nuptial coloration in turbid conditions. Our findings suggest that anthropogenic disturbance to the signaling environment can potentially reduce the evolutionary potential of sexual selection by diminishing the efficacy of visual displays and weakening socially enforced signals of male quality.
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