| 31. |
- Maklakov, Alexei A., et al.
(författare)
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Brains and the city : big-brained passerine birds succeed in urban environments
- 2011
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Ingår i: Biology Letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 7:5, s. 730-732
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Tidskriftsartikel (refereegranskat)abstract
- Urban regions are among the most human-altered environments on Earth and they are poised for rapid expansion following population growth and migration. Identifying the biological traits that determine which species are likely to succeed in urbanized habitats is important for predicting global trends in biodiversity. We provide the first evidence for the intuitive yet untested hypothesis that relative brain size is a key factor predisposing animals to successful establishment in cities. We apply phylogenetic mixed modelling in a Bayesian framework to show that passerine species that succeed in colonizing at least one of 12 European cities are more likely to belong to big-brained lineages than species avoiding these urban areas. These data support findings linking relative brain size with the ability to persist in novel and changing environments in vertebrate populations, and have important implications for our understanding of recent trends in biodiversity.
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| 32. |
- Maklakov, Alexei A., et al.
(författare)
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Brains and the city in passerine birds : re-analysis and confirmation of the original result
- 2013
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Ingår i: Biology Letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 9:6, s. 20130859-
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Tidskriftsartikel (refereegranskat)abstract
- Our original paper [1] included two Bayesian analyses [2] of the association between brain size and the probability of a passerine species of bird breeding in the city centre—at the level of families and at the level of individual species—with both analyses suggesting the same pattern. It has since been brought to our attention that in one of the analyses at the level of individual species, the residual variance was not fixed to 1 resulting in overestimation of the variance. We re-ran the analysis using fixed residual variance and the results support the original conclusion that relative brain size is associated with breeding in the city centre (ln brain size: posterior mean, 324.53, 95% credibility interval, 52.61–601.35; ln body size: posterior mean, −276.22, 95% credibility interval, −490.60 to −70.32). Furthermore, we applied a complimentary approach using logistic regression to test whether brain size predicts breeding in the city centre (yes/no) without accounting for phylogeny. This analysis also resulted in a significant positive association between brain size and breeding in city centres (likelihood ratio tests: ln brain size: d.f. = 1, χ2 = 11.08, p = 0.0009; ln body size: d.f. = 1, χ2 = 11.26, p = 0.0008). Thus, our results are confirmed by both phylogenetic and non-phylogenetic analyses.
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| 33. |
- Maklakov, Alexei A., et al.
(författare)
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The effect of sexual harassment on lethal mutation rate in female Drosophila melanogaster
- 2013
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - London, UK : The Royal Society. - 0962-8452 .- 1471-2954. ; 280:1750, s. 20121874-
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Tidskriftsartikel (refereegranskat)abstract
- The rate by which new mutations are introduced into a population may have far-reaching implications for processes at the population level. Theory assumes that all individuals within a population have the same mutation rate, but this assumption may not be true. Compared with individuals in high condition, those in poor condition may have fewer resources available to invest in DNA repair, resulting in elevated mutation rates. Alternatively, environmentally induced stress can result in increased investment in DNA repair at the expense of reproduction. Here, we directly test whether sexual harassment by males, known to reduce female condition, affects female capacity to alleviate DNA damage in Drosophila melanogaster fruitflies. Female gametes can repair double-strand DNA breaks in sperm, which allows manipulating mutation rate independently from female condition. We show that male harassment strongly not only reduces female fecundity, but also reduces the yield of dominant lethal mutations, supporting the hypothesis that stressed organisms invest relatively more in repair mechanisms. We discuss our results in the light of previous research and suggest that social effects such as density and courtship can play an important and underappreciated role in mediating condition-dependent mutation rate.
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| 34. |
- Maklakov, Alexei A., et al.
(författare)
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The Expensive Germline and the Evolution of Ageing
- 2016
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Ingår i: Current Biology. - : Elsevier BV. - 0960-9822 .- 1879-0445. ; 26:13, s. R577-R586
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Forskningsöversikt (refereegranskat)abstract
- The trade-off between survival and reproduction is the bedrock of the evolutionary theory of ageing. The reproductive system regulates ageing of the soma, and removal of germ cells extends somatic lifespan and increases resistance to a broad variety of abiotic and biotic stresses. The general explanation for this somatic response is that reduced reproduction frees up resources for survival. Remarkably, however, the disruption of molecular signaling pathways that regulate ageing increases lifespan without the obligatory reduction in fecundity, thus challenging the key role of the survival-reproduction trade-off. Here, we review the diverse literature on the costs of lifespan extension and suggest that the current paradigm is overly centered on the trade-off between lifespan and fecundity, often neglecting key aspects of fitness, such as development time, defense against parasites and, in particular, the high costs of germline maintenance. Compromised germline maintenance increases germline mutation rate, which reduces offspring fitness and ultimately can terminate germline proliferation across generations. We propose that future work should incorporate the costs of germline maintenance in the study of ageing evolution, as well as in applied biomedical research, by assessing offspring fitness.
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| 35. |
- Nieuwenhuis, Bart P. S., et al.
(författare)
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Repeated evolution of self-compatibility for reproductive assurance
- 2018
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Sexual reproduction in eukaryotes requires the fusion of two compatible gametes of opposite sexes or mating types. To meet the challenge of finding a mating partner with compatible gametes, evolutionary mechanisms such as hermaphroditism and self-fertilization have repeatedly evolved. Here, by combining the insights from comparative genomics, computer simulations and experimental evolution in fission yeast, we shed light on the conditions promoting separate mating types or self-compatibility by mating-type switching. Analogous to multiple independent transitions between switchers and non-switchers in natural populations mediated by structural genomic changes, novel switching genotypes readily evolved under selection in the experimental populations. Detailed fitness measurements accompanied by computer simulations show the benefits and costs of switching during sexual and asexual reproduction, governing the occurrence of both strategies in nature. Our findings illuminate the trade-off between the benefits of reproductive assurance and its fitness costs under benign conditions facilitating the evolution of self-compatibility.
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| 36. |
- Nieuwenhuis, Bart P. S., et al.
(författare)
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The evolution of mating-type switching for reproductive assurance
- 2016
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Ingår i: Bioessays. - : Wiley. - 0265-9247 .- 1521-1878. ; 38:11, s. 1141-1149
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Forskningsöversikt (refereegranskat)abstract
- Alternative ways to ensure mate compatibility, such as hermaphroditism and the breakdown of self-incompatibility, evolved repeatedly when finding a mating partner is difficult. In a variety of microorganisms where compatibility is determined by mating-types, a highly regulated form of universal compatibility system called mating-type switching has evolved several times. This sophisticated system allows for the genetic adjustment of the mating type during asexual growth, and it most likely evolved for reproductive assurance of immotile species under low densities. In this review, we compare the switching strategy to other universal compatibility systems such as unisexual mating and homothallism. We identify the costs of switching, including genome instability, and mechanistic costs, as well as the benefits, mainly the maintenance of important mating-type functions. Given the potential benefits of mating-type switching, we speculate that switching is likely to have evolved many times independently, and may be more common in groups where genetic mating types regulate mate compatibility than assumed so far.
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| 37. |
- Otto, Sarah P., et al.
(författare)
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Evolution of haploid selection in predominantly diploid organisms
- 2015
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 112:52, s. 15952-15957
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Tidskriftsartikel (refereegranskat)abstract
- Diploid organisms manipulate the extent to which their haploid gametes experience selection. Animals typically produce sperm with a diploid complement of most proteins and RNA, limiting selection on the haploid genotype. Plants, however, exhibit extensive expression in pollen, with actively transcribed haploid genomes. Here we analyze models that track the evolution of genes that modify the strength of haploid selection to predict when evolution intensifies and when it dampens the "selective arena" within which male gametes compete for fertilization. Considering deleterious mutations, evolution leads diploid mothers to strengthen selection among haploid sperm/pollen, because this reduces the mutation load inherited by their diploid offspring. If, however, selection acts in opposite directions in haploids and diploids ("ploidally antagonistic selection"), mothers evolve to reduce haploid selection to avoid selectively amplifying alleles harmful to their offspring. Consequently, with maternal control, selection in the haploid phase either is maximized or reaches an intermediate state, depending on the deleterious mutation rate relative to the extent of ploidally antagonistic selection. By contrast, evolution generally leads diploid fathers to mask mutations in their gametes to the maximum extent possible, whenever masking (e.g., through transcript sharing) increases the average fitness of a father's gametes. We discuss the implications of this maternal-paternal conflict over the extent of haploid selection and describe empirical studies needed to refine our understanding of haploid selection among seemingly diploid organisms.
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| 38. |
- Parker, G. A., et al.
(författare)
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Sperm competition games : Sperm size (mass) and number under raffle and displacement, and the evolution of P-2
- 2010
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Ingår i: Journal of Theoretical Biology. - : Elsevier BV. - 0022-5193 .- 1095-8541. ; 264:3, s. 1003-1023
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Tidskriftsartikel (refereegranskat)abstract
- We examine models for evolution of sperm size (i.e. mass m) and number (s) under three mechanisms of sperm competition at low 'risk' levels: (i) raffle with no constraint on space available for competing sperm, (ii) direct displacement mainly by seminal fluid, and (iii) direct displacement mainly by sperm mass. Increasing sperm mass increases a sperm's 'competitive weight' against rival sperm through a diminishing returns function, r(m). ESS total ejaculate expenditure (the product m*s*) increases in all three models with sperm competition risk, q. If r(m), or ratio r'(m)/r(m), is independent of ESS sperm numbers, ESS sperm mass remains constant, and the sperm mass/number ratio (m*/s*) therefore decreases with risk. Dependency of sperm mass on risk can arise if r(m) depends on competing sperm density (sperm number / space available for sperm competition). Such dependencies generate complex relationships between sperm mass and number with risk, depending both on the mechanism and how sperm density affects r(m). While numbers always increase with risk, mass can either increase or decrease, but m*/s* typically decreases with risk unless sperm density strongly influences r(m). Where there is no extrinsic loading due to mating order, ESS paternity of the second (i.e. last) male to mate (P-2) under displacement always exceeds 0.5, and increases with risk (in the raffle P-2 = 0.5). Caution is needed when seeking evidence for a sperm size-number trade off. Although size and number trade-off independently against effort spent on acquiring matings, their product, m*s*, is invariant or fixed at a given risk level, effectively generating a size-number trade off. However, unless controlled for the effects of risk, the relation between m* and s* can be either positive or negative (a positive relation is usually taken as evidence against a size-number trade off).
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| 39. |
- Promerová, Marta, et al.
(författare)
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No evidence for MHC class II-based non-random mating at the gametic haplotype in Atlantic salmon
- 2017
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Ingår i: Heredity. - : Springer Science and Business Media LLC. - 0018-067X .- 1365-2540. ; 118:6, s. 563-567
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Tidskriftsartikel (refereegranskat)abstract
- Genes of the major histocompatibility complex (MHC) are a likely target of mate choice because of their role in inbreeding avoidance and potential benefits for offspring immunocompetence. Evidence for female choice for complementary MHC alleles among competing males exists both for the pre- and the postmating stages. However, it remains unclear whether the latter may involve non-random fusion of gametes depending on gametic haplotypes resulting in transmission ratio distortion or non-random sequence divergence among fused gametes. We tested whether non-random gametic fusion of MHC-II haplotypes occurs in Atlantic salmon Salmo salar. We performed in vitro fertilizations that excluded interindividual sperm competition using a split family design with large clutch sample sizes to test for a possible role of the gametic haplotype in mate choice. We sequenced two MHC-II loci in 50 embryos per clutch to assess allelic frequencies and sequence divergence. We found no evidence for transmission ratio distortion at two linked MHC-II loci, nor for non-random gamete fusion with respect to MHC-II alleles. Our findings suggest that the gametic MHC-II haplotypes play no role in gamete association in Atlantic salmon and that earlier findings of MHC-based mate choice most likely reflect choice among diploid genotypes. We discuss possible explanations for these findings and how they differ from findings in mammals.
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| 40. |
- Sáez-Espinosa, Paula, et al.
(författare)
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Morphological and ultrastructural alterations of zebrafish (Danio rerio) spermatozoa after motility activation
- 2022
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Ingår i: Theriogenology. - : Elsevier BV. - 0093-691X. ; 188, s. 108-115
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Tidskriftsartikel (refereegranskat)abstract
- Spermatozoa motility in freshwater and marine fish is mainly controlled by the difference in osmotic pressure. Specifically, zebrafish (Danio rerio) spermatozoa undergo hypoosmotic shock due to the decrease in extracellular potassium, which leads to membrane hyperpolarization and activation of flagellar motility. Previous studies have concluded that motility activation has a negative effect on the spermatozoa structure. However, no evidence exists about ultrastructural changes in zebrafish spermatozoa after motility activation. In this study, spermatozoa samples were obtained from ten adult zebrafish individuals before and 60 s after motility activation and analyzed using Scanning and Transmission Electron Microscopy. Results showed dramatic morphological and ultrastructural alterations of the zebrafish spermatozoa after activation. In particular, the spermatozoa head underwent severe morphological distortion, including swelling of the nucleus, the bursting of the plasma membrane, and the alteration of the genetic material. Midpieces were also affected after activation since rupture of the cell membrane and lysis of mitochondria occurred. Furthermore, after the hypoosmotic shock, most spermatozoa showed a coiled flagellum and a disaggregated plasma membrane. Overall, our findings show that the activation of motility leads to substantial zebrafish spermatozoa morphological and ultrastructural changes, which could modify their physiology and decrease the fertilizing potential.
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