Variation in female aggression in 2 three-spined stickleback populations with female throat and spine coloration

Despite growing interest in female ornament evolution, we still have a rudimentary understanding of female display traits relative to similar traits in males. Under one popular adaptive scenario, fe- male ornaments are hypothesized to function in female–female competition and serve as badges of status, such that their expression is linked with elevated aggression in some cases. In this study, we investigated the relationship between 2 female ornaments—male-like red throat color and red spine coloration—and female aggression in 2 independently derived stream-resident populations of three-spined stickleback Gasterosteus aculeatus. Using simulated intrusions, we tested whether females with redder ornaments were generally more aggressive, and for variation in aggressive and social behaviors between the 2 populations. We found that the red intensity of the throat and spine did not predict aggression levels in either population, suggesting a limited role for both fe- male ornaments during female–female interaction. The 2 populations exhibited different levels of aggressive behaviors, unrelated to the color patches. Our results suggest that variation in selective pressures between populations may promote interpopulation variance in aggressive behavior but not the correlation between female ornamentation and aggression, and raise the possibility that red coloration may have evolved through different mechanisms or processes in the 2 populations

Partial sex linkage and linkage disequilibrium on the guppy sex chromosome

The guppy Y chromosome has been considered a model system for the evolution of suppressed recombination between sex chromosomes, and it has been proposed that complete sex‐linkage has evolved across about 3 Mb surrounding this fish's sex‐determining locus, followed by recombination suppression across a further 7 Mb of the 23 Mb XY pair, forming younger “evolutionary strata”. Sequences of the guppy genome show that Y is very similar to the X chromosome. Knowing which parts of the Y are completely nonrecombining, and whether there is indeed a large completely nonrecombining region, are important for understanding its evolution. Here, we describe analyses of PoolSeq data in samples from within multiple natural populations from Trinidad, yielding new results that support previous evidence for occasional recombination between the guppy Y and X. We detected recent demographic changes, notably that downstream populations have higher synonymous site diversity than upstream ones and other expected signals of bottlenecks. We detected evidence of associations between sequence variants and the sex‐determining locus, rather than divergence under a complete lack of recombination. Although recombination is infrequent, it is frequent enough that associations with SNPs can suggest the region in which the sex‐determining locus must be located. Diversity is elevated across a physically large region of the sex chromosome, conforming to predictions for a genome region with infrequent recombination that carries one or more sexually antagonistic polymorphisms. However, no consistently male‐specific variants were found, supporting the suggestion that any completely sex‐linked region may be very small

Has recombination changed during the recent evolution of the guppy Y chromosome?

Genome sequencing and genetic mapping of molecular markers have demonstrated nearly complete Y-linkage across much of the guppy (Poecilia reticulata) XY chromosome pair. Predominant Y-linkage of factors controlling visible male-specific coloration traits also suggested that these polymorphisms are sexually antagonistic (SA). However, occasional exchanges with the X are detected, and recombination patterns also appear to differ between natural guppy populations, suggesting ongoing evolution of recombination suppression under selection created by partially sex-linked SA polymorphisms. We used molecular markers to directly estimate genetic maps in sires from four guppy populations. The maps are very similar, suggesting that their crossover patterns have not recently changed. Our maps are consistent with population genomic results showing that variants within the terminal 5 Mb of the 26.5 Mb sex chromosome, chromosome 12, are most clearly associated with the maleness factor, albeit incompletely. We also confirmed occasional crossovers proximal to the male-determining region, defining a second, rarely recombining, pseudo-autosomal region, PAR2. This fish species may therefore have no completely male-specific region (MSY) more extensive than the male-determining factor. The positions of the few crossover events suggest a location for the male-determining factor within a physically small repetitive region. A sex-reversed XX male had few crossovers in PAR2, suggesting that this region’s low crossover rate depends on the phenotypic, not the genetic, sex. Thus, rare individuals whose phenotypic and genetic sexes differ, and/or occasional PAR2 crossovers in males can explain the failure to detect fully Y-linked variants

Male red throat coloration, pelvic spine coloration, and courtship behaviours in threespine stickleback

Background: In addition to exhibiting red nuptial throat coloration, male threespine sticklebacks (Gasterosteus aculeatus) often possess red coloration on their pelvic spines. Although variation in throat colour has been shown to be associated with male reproductive behaviour, limited research has been devoted to the behavioural correlates of red spine colour. Like the red throat, spine colour might correlate with components of male reproductive behaviour and may also be androgen dependent, with important implications for a potential signalling function. Hypothesis: Spine coloration, like throat coloration, is correlated with components of courtship behaviour, and also with the fish androgen 11-ketotestosterone (11KT). Methods: To examine the role of male throat and spine colour expression in a mating context, we measured the behavioural response of nesting males to conspecific females. We analysed the relationships between throat and spine colours with reproductive behaviours as well as with 11KT. Results: Males with more intensely red throats courted females more vigorously, whereas males with redder spines displayed relatively more aggressive behaviour during courtship. An initial analysis of a subsample of males showed that 11KT was positively associated with spine colour intensity, but not with red throats or any behaviours. Hence throat and spine colour may reflect different components of male reproductive behaviour, and 11KT is a potential mediator of spine coloration in males

Fishing For The Evolutionary Bases Of Female Ornamentation

Sexual dimorphism, or phenotypic differentiation of the sexes, is widespread amongst animals. It is understood mainly in the context of sexual selection, i.e. selection on mating success, with such selection typically acting more strongly on males. In some cases however, conspicuous ornaments similar to those observed in males are expressed in females—but the causes for their evolution have often been elusive. In my dissertation I examine the behavioral, hormonal, and genetic correlates of female throat coloration—a male typical trait—in the threespine stickleback fish (Gasterosteus aculeatus), to test whether the evolution of the female trait might be attributed to adaptive or nonadaptive mechanisms. My results indicate that while male-typical throat color in females is associated with some components of fitness, e.g. body size and growth, it does not reflect reproductive readiness or body condition. Also, red-throated females are not socially more dominant or aggressive than dull-throated females in either dyadic or socially complex contexts. Further, the masculinized female trait is not associated with variation in fish-specific androgen mechanisms, 11-ketotestosterone and its cognate receptor, suggesting that the female trait is not under the principal male-specific endocrine control. Investigating the genetic basis of throat coloration I find that that the same genomic regions are associated with the presence of red throat coloration in both sexes, suggesting that female throat coloration might be a genetically correlated byproduct of selection on males. In sum, using an interdisciplinary approach to studying the evolutionary causes of female ornaments, I find that the red throat in female sticklebacks is potentially a nonadaptive trait that has arisen due to a genetic correlation between the sexes; thus female conspicuous traits do not necessarily result from adaptive processes related to sexual selection on females.Ph.D

Fishing For The Evolutionary Bases Of Female Ornamentation

Sexual dimorphism, or phenotypic differentiation of the sexes, is widespread amongst animals. It is understood mainly in the context of sexual selection, i.e. selection on mating success, with such selection typically acting more strongly on males. In some cases however, conspicuous ornaments similar to those observed in males are expressed in females—but the causes for their evolution have often been elusive. In my dissertation I examine the behavioral, hormonal, and genetic correlates of female throat coloration—a male typical trait—in the threespine stickleback fish (Gasterosteus aculeatus), to test whether the evolution of the female trait might be attributed to adaptive or nonadaptive mechanisms.\r\nMy results indicate that while male-typical throat color in females is associated with some components of fitness, e.g. body size and growth, it does not reflect reproductive readiness or body condition. Also, red-throated females are not socially more dominant or aggressive than dull-throated females in either dyadic or socially complex contexts. Further, the masculinized female trait is not associated with variation in fish-specific androgen mechanisms, 11-ketotestosterone and its cognate receptor, suggesting that the female trait is not under the principal male-specific endocrine control.\r\nInvestigating the genetic basis of throat coloration I find that that the same genomic regions are associated with the presence of red throat coloration in both sexes, suggesting that female throat coloration might be a genetically correlated byproduct of selection on males. In sum, using an interdisciplinary approach to studying the evolutionary causes of female ornaments, I find that the red throat in female sticklebacks is potentially a nonadaptive trait that has arisen due to a genetic correlation between the sexes\; thus female conspicuous traits do not necessarily result from adaptive processes related to sexual selection on females

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