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3,283 results for “males and females”
Data from: The evolution of sex similarities in social signals: Climatic seasonality is associated with lower sexual dimorphism and greater elaboration of female and male signals in antbirds (Thamnophilidae)
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Data from: The coevolution of male and female genitalia in a mammal: a quantitative genetic insight
<p>Male genitalia are among the most phenotypically diverse morphological traits, and sexual selection is widely accepted as being responsible for their evolutionary divergence. Studies of house mice suggest that the shape of the baculum (penis bone) affects male reproductive fitness and experimentally imposed postmating sexual selection has been shown to drive divergence in baculum shape across generations. Much less is known of the morphology of female genitalia and its coevolution with male genitalia. In light of this, we used a paternal half-sibling design to explore patterns of additive genetic variation and covariation underlying baculum shape and female vaginal tract size in house mice (Mus musculus domesticus). We applied a landmark-based morphometrics approach to measure baculum size and shape in males and the length of the vaginal tract and width of the cervix in females. Our results reveal significant additive genetic variation in house mouse baculum morphology and cervix width, as well as evidence for genetic covariation between male and female genital measures. Our data thereby provide novel insight into the potential for the coevolutionary divergence of male and female genital traits in a mammal. </p>
Data from: Testing the greater male variability hypothesis: male mountain chickadees exhibit larger variation in reversal learning compared to females
The 'greater male variability hypothesis' predicts that males exhibit larger ranges of variation in cognitive performance compared to females, however, support for this hypothesis has come exclusively from studies of humans. This scenario aligns with the fact that the vast majority of the literature assessing sex differences in cognition is based on studies of humans and a few other mammals. In order to elucidate the underpinnings of cognitive variation and the potential for fitness consequences, we must investigate sex differences in cognition in non-mammalian systems as well. Here we assess the performance of male and female food-caching birds on a spatial learning and memory task and a reversal spatial task to address whether there are sex differences in mean cognitive performance or in the range of variation in performance. For both tasks, male and female mean performance was similar across four years of testing; however, males did exhibit a wider range of variation in performance on the reversal spatial task compared to females. The implications for mate choice and sexual selection of cognitive abilities are discussed, with a call for further investigation into sex-related cognitive variation.
Data from: Effects of female group size on the number of males in blue monkey (Cercopithecus mitis) groups
<p>The number of males per group varies substantially in group-living primates, both between and within species. In blue monkeys (<i>Cercopithecus mitis</i>), males may temporarily join groups during annual mating seasons when sexually receptive females are present. A likely determinant of the number of males per group is female group size (the number of adult females in a group). To clarify the role of female group size in driving variation in the number of males per group, we expanded on earlier observations of a wild population in the Kakamega Forest, Kenya with a larger sample of groups that varied five-fold in female group size. We found considerable flexibility in social organization, with groups experiencing multi-male episodes both during and outside mating seasons, some persisting over multi-year periods. The dichotomy between single- and multi-male mating seasons was less distinct than previously reported, suggesting greater variation in multi-male states. Across 65 group-specific conception periods, female group size strongly influenced how often multiple sexually active females and multiple males were present in a group. The number of sexually active females present on a given day related closely to the number of males in the group that same day, especially during conception periods. Results suggest that males join and remain in larger groups where mating opportunities are greater and costs of joining or staying may be lower than in smaller groups. This longitudinal study highlights intraspecific social variation within and across groups while confirming that female group size influences the number of males.</p>
How female × male and male × male interactions influence competitive fertilization in Drosophila melanogaster
How males and females contribute to joint reproductive success has been a long-standing question in sexual selection. Under postcopulatory sexual selection (PSS), paternity success is predicted to derive from complex interactions among females engaging in cryptic female choice and males engaging in sperm competition. Such interactions have been identified as potential sources of genetic variation in sexually selected traits but are also expected to inhibit trait diversification. To date, studies of interactions between females and competing males have focused almost exclusively on genotypes and not phenotypic variation in sexually selected traits. Here, we characterize within- and between-sex interactions in Drosophila melanogaster using isogenic lines with heritable variation in both male and female traits known to influence competitive fertilization. We confirmed, and expanded on, previously reported genotypic interactions within and between the sexes, and showed that several reproductive events, including sperm transfer, female sperm ejection and sperm storage, were explained by two- and three-way interactions among sex-specific phenotypes. We also documented complex interactions between the lengths of competing males' sperm and the female seminal receptacle, which are known to have experienced rapid female-male co-diversification. Our results highlight the non-independence of sperm competition and cryptic female choice and demonstrate that complex interactions between the sexes do not limit the ability of multivariate systems to respond to directional sexual selection.
Experimentally induced intrasexual mating competition and sex-specific evolution in female and male nematodes
Sexual dimorphism in life history traits and their trade-offs is widespread among sexually reproducing animals, and is strongly influenced by the differences in reproductive strategies between the sexes. We investigated how intrasexual competition (pre- and postcopulatory) acted on specific life history traits, important to fitness, and their trade-offs in the outcrossing nematode Caenorhabditis remanei. Here, we imposed strong sex-specific selection through experimental evolution with increased potential for intrasexual competition by skewing the adult sex ratio towards either males or females (1:10 or 10:1) over 30 generations, and subsequently measured the phenotypic response to selection in three traits related to fitness; body size, fecundity and tolerance to heat stress. We observed a stronger response to selection in females for body size and peak fitness, suggesting that females may experience stronger net selection and potentially harbour higher amounts of standing genetic variance compared to males. Our study highlights the importance of investigating direct and indirect effects of intrasexual competition in both sexes in order to capture sex-specific responses and understand the evolution of sexual dimorphism in traits expressed by both sexes.
Colorful traits in avian females, individual condition, reproductive performance, and male mate preferences: A meta-analytic approach
<p>Colorful ornaments in females are suggested to have evolved and be maintained by sexual selection. Although several studies have evaluated this idea evidence is still equivocal. Results from empirical studies have been compilated in reviews, but quantitative analyses have seldom been performed. Here, using a meta-analytic approach, we show that evidence from empirical studies conducted in birds, supports the ideas that colorful female ornaments are positively associated with individual condition, reproductive performance, and male-mate preferences. Hence, females' colorful traits, in birds, likely evolved and are maintained by sexual selection.</p>
Female and male plumage colour is linked to parental quality, pairing and extra-pair mating in a tropical passerine
<p>Sexual selection has been proposed to drive the evolution of elaborate phenotypic traits in males, which often confer success in competition or mating. However, in many species both males and females display such traits, although studies investigating selection acting in both sexes are scarce. In this study, we investigated whether plumage ornamentation is sexually selected in female and male lovely fairy-wrens <em>Malurus amabilis</em>, a cooperatively breeding songbird. We found that female and male plumage colour was correlated with parental quality but not with individual quality and survival. We also found evidence of positive assortative mating based on plumage colour. Microsatellite analyses of paternity indicated that the lovely fairy-wren has high levels of extra-pair paternity, with 53% of offspring (in 58% of broods, of 57% of females) resulting from extra-pair mating. Female and male plumage colour did not predict reproductive success or the proportion of extra-pair offspring in their own nest, but less colourful males obtained higher extra-pair paternity when paired with more colourful females, and gained overall higher total paternity (own nest and other nests). We argue that plumage colour may be under sex-specific selection, highlighting the importance of looking at both sexes in studies of sexual selection and ornament evolution. The current findings together with previous study, suggest that plumage colour in female and male lovely fairy-wrens appears to be an honest signal relevant in both intra and inter-sexual competition contexts.</p>
Data from: Separating differential allocation by females from direct effects of male condition in a beetle
<p>Differential allocation is the adjustment of reproductive allocation, typically by a female, in response to the quality of her male partner. A recent theoretical model suggests that differential allocation may influence trade-offs between reproductive traits within a breeding attempt. Furthermore, it is often difficult to distinguish differential allocation from direct effects of male condition. We address these gaps using a novel cross-fostering design to exclude direct effects of male condition and to test whether differential allocation affects trade-offs between and within breeding attempts. This design detects differential allocation as effects of a female's mating partner and direct effects of male condition as effects of the larvae's sire. We used the burying beetle Nicrophorus vespilloides, a species which adjusts reproductive allocation by culling some larvae after hatching. We used food-deprivation to manipulate the nutritional condition of both the female's mating partner and the larvae's sire. We find clear evidence for differential allocation as females mating with food-deprived males had fewer larvae than females mating with control males. There was a trade-off between number and size of larvae when females mated with control males, but a positive relationship when females mated with food-deprived males. Thus, differential allocation influenced relationships between reproductive traits within a breeding attempt, but not necessarily through trade-offs. Instead, we suggest that there may be cryptic heterogeneity in quality among females or their mating partners that was only exposed when females mated with a male in poor condition.</p>
Different effects of mating group size as male and as female on sex allocation in a simultaneous hermaphrodite
<p>Sex allocation theory predicts that the optimal sexual resource allocation of simultaneous hermaphrodites is affected by mating group size (MGS). Although the original concept assumes that the MGS does not differ between male and female functions, the MGS in the male function (MGSm; i.e., the number of sperm recipients the focal individual can deliver its sperm to plus one) and that in the female function (MGSf; the number of sperm donors plus one) do not always coincide and may differently affect the optimal sex allocation. Moreover, reproductive costs can be split into "variable" (e.g., sperm and eggs) and "fixed" (e.g., genitalia) costs, but these have been seldom distinguished in empirical studies. We examined the effects of MGSm and MGSf on the fixed and variable reproductive investments in the sessilian barnacle <i>Balanus rostratus</i>. The results showed that MGSm had a positive effect on sex allocation, whereas MGSf had a nearly significant negative effect. Moreover, the "fixed" cost varied with body size and both aspects of MGS. We argue that the two aspects of MGS should be distinguished for organisms with unilateral mating.</p>
Web wars: Males of the golden orb-web spider invest more in fights for mated and aggregated females
<p>In addition to resource value, the cost of finding mates may affect how much males invest in fights for females. The cost of finding females may be imposed through natural factors extrinsic to males, such as female spatial distribution and predation pressure, which can be challenging to simulate in laboratory conditions. Therefore, studies under natural conditions may be suitable for understanding how the costs of finding mating partners affect male investment in fights. We used the spider <i>Trichonephila clavipes </i>to evaluate the hypotheses that males in field conditions invest more in contests for access to (1) unmated and (2) more fecund females, and (3) when access to females is harder. To test these hypotheses, we recorded the occurrence, duration and escalation of induced contests between males located in webs of females that differed in reproductive status (estimated by female life stage), fecundity (estimated by female abdominal area) and spatial distribution (i.e. isolated or aggregated with webs of other females). The occurrence and duration of contests were unrelated to female value or search costs. However, the probability for escalation was higher when males were fighting for adult (and probably mated) females. We also found that males tended to start a contest more often in aggregated webs. These results indicate that males of <i>T. clavipes</i> adjust investment in contests, but contrarily to what we expected. We suggest males invest more in contests for adult females because they are defending females that they previously fertilized to avoid sperm competition.</p>
No evidence for divergence in male harmfulness or female resistance in response to changes in the opportunity for dispersal
The outcome of sexual conflict can depend on the social environment, as males respond to changes in the inclusive fitness payoffs of harmfulness and harm females less when they compete with familiar relatives. Theoretical models also predict that if limited male dispersal predictably enhances local relatedness while maintaining global competition, kin selection can produce evolutionary divergences in male harmfulness among populations. Experimental tests of these predictions, however, are rare. We assessed rates of dispersal in female and male seed beetles Callosobruchus maculatus, a model species for studies of sexual conflict, in an experimental setting. Females dispersed significantly more often than males, but dispersing males travelled just as far as dispersing females. Next, we used experimental evolution to test whether limiting dispersal allowed the action of kin selection to affect divergence in male harmfulness and female resistance. Populations of C. maculatus were evolved for 20 and 25 generations under one of three dispersal regimens: completely free dispersal, limited dispersal, and no dispersal. There was no divergence among treatments in female reproductive tract scarring, ejaculate size, mating behaviour, fitness of experimental females mated to stock males, or fitness of stock females mated to experimental males. We suggest that this is likely due to insufficient strength of kin selection rather than a lack of genetic variation or time for selection. Limited dispersal alone is therefore not sufficient for kin selection to reduce male harmfulness in this species, consistent with general predictions that limited dispersal will only allow kin selection if local relatedness is independent of the intensity of competition among kin.
Data from: Divergent male and female mate preferences do not explain incipient speciation between lizard lineages
<p>Diversification in sexual signals is often taken as evidence for the importance of sexual selection in speciation. However, in order for sexual selection to generate reproductive isolation between populations, both signals and mate preferences must diverge together. Furthermore, assortative mating may result from multiple behavioural mechanisms, including female mate preferences, male mate preferences and male-male competition; yet their relative contributions are rarely evaluated. Here, we explored the role of mate preferences and male competitive ability as potential barriers to gene flow between two divergent lineages of the tawny dragon lizard, Ctenophorus decresii, which differ in male throat coloration. We found stronger behavioural barriers to pairings between southern lineage males and northern lineage females than between northern males and southern females, indicating incomplete and asymmetric behavioural isolating barriers. These results were driven by both male and female mate preferences rather than lineage differences in male competitive ability. Intrasexual selection is therefore unlikely to drive the outcome of secondary contact in C. decresii, despite its widely acknowledged importance in lizards. Our results are consistent with the emerging view that although both male and female mate preferences can diverge alongside sexual signals, speciation is rarely driven by divergent sexual selection alone.</p> <p> </p>
Data from: Testosterone activates sexual dimorphism including male-typical carotenoid but not melanin plumage pigmentation in a female bird
In males it is frequently testosterone (T) that activates the expression of sexually selected morphological and behavioral displays, but the role of T in regulating similar traits in females is less clear. Here we combine correlational data with results from T and gonadotropin-releasing hormone (GnRH) manipulations in both sexes to assess the role of T in mediating sexually dimorphic coloration and morphology in the red-backed fairy-wren (Malurus melanocephalus). We show that (1) natural variation in female expression of ornamental traits (darkened bills and red back feathers) are positively associated with age and circulating androgen titres, (2) females have the capacity to express most male-typical traits in response to exogenous T, including carotenoid-pigmented body plumage, shorter feathers, darkened bill, and enlarged cloacal protuberance, but (3) appear constrained in production of male-typical melanin-pigmented plumage, and (4) low androgen levels during the pre-nuptial molt, probably due to low ovarian capacity for steroid production (or LH-sensitivity), prevent females from developing male-like ornamentation. Thus, females appear to retain molecular mechanism for hormonally regulated male-typical ornamentation, although these are rarely activated because of insufficient production of the hormonal signal.
Data from: Reproductive character displacement of female, but not male song discrimination in an avian hybrid zone
Divergence of male sexual signals and female preferences for those signals often maintains reproductive boundaries between closely related, co-occurring species. However, contrasting sources of selection, such as interspecific competition, can lead to weak divergence or even convergence of sexual signals in sympatry. When signals converge, assortative mating can be maintained if the mating preferences of females diverge in sympatry (reproductive character displacement; RCD), but there are few explicit examples. Pied flycatchers (Ficedula hypoleuca) are sympatric with collared flycatchers (F. albicollis) on the Baltic island of Öland, where males from both species compete over nestboxes, their songs converge, and the two species occasionally hybridize. We compare song discrimination of male and female pied flycatchers on Öland and in an allopatric population on the Swedish mainland. Using field choice trials, we show that male pied flycatchers respond similarly to the songs of both species in sympatry and in allopatry, while female pied flycatchers express stronger discrimination against heterospecific songs in sympatry than in allopatry. These results are consistent with RCD of song discrimination of female pied flycatchers where they co-occur with collared flycatchers, which should maintain species assortative mating despite convergence of male sexual signals.
Data from: A weapons-testes trade-off in males is amplified in female traits
Sexually selected weapons are assumed to trade off with traits related to ejaculates, such as testes. Yet, remarkably little is known about what governs resource allocation and why trade-offs are found in some cases and not others. Often-used models depict competitive allocation occurring within the functional grouping of traits (e.g., reproduction); however, other factors including tissue expense and developmental timing may influence allocation. Experimental comparisons of investment across the sexes have the potential to illuminate allocation rules, because the sexes do not always use traits for the same functions. Here, we capitalize upon a species where females have weapons-testes homologues. We report that a documented trade-off in investment between hind-limb weapons and testes in leaf-footed cactus bugs, Narnia femorata, is even more pronounced in female hind limbs and ovaries. Female hind limbs in this species do not share the clear reproductive function of male hind limbs, therefore this trade-off spans trait functional groups. Such patterns of investment suggest that future studies of reproductive trade-offs should consider factors such as tissue expense and developmental timing.
Does operational sex ratio influence relative strength of purging selection in males vs. females?
<p>According to theory, sexual selection in males may efficiently purge mutation load of sexual populations, reducing or fully compensating "the cost of males". For this to occur, mutations not only need to be deleterious to both sexes, they also must affect males more than females. A frequently overlooked problem is that relative strength of selection on males vs. females may vary between environments, with social conditions being particularly likely to affect selection in males and females differently. Here we induced mutations in red flour beetles (Tribolium castaneum) and tested their effect in both sexes under three different operational sex ratios (1:2, 1:1, 2:1). Induced mutations decreased fitness of both males and females, but their effect was not stronger in males. Surprisingly, operational sex ratio did not affect selection against deleterious mutations nor its relative strength in the sexes. Thus, our results show no support for the role of sexual selection in the evolutionary maintenance of sex.</p> <p> </p>
Data from: Correlated divergence of female and male genitalia in replicated lineages with ongoing ecological speciation
Divergence of genital traits among lineages has the potential to serve as a reproductive isolating barrier when copulation, insemination, or fertilization are inhibited by incompatibilities between female and male genitalia. Despite widespread evidence for genital trait diversity among closely related lineages and coevolution of female and male genitalia within lineages, few studies have investigated genital evolution during the early stages of speciation. We quantified genital variation in replicated population pairs of Poecilia mexicana with ongoing ecological speciation between sulfidic (H2S-containing) and nearby non-sulfidic habitats. These analyses revealed rapid and correlated divergence of female and male genitalia across evolutionarily independent population pairs exposed to divergent selection regimes. Both sexes exhibited convergent evolution of genital traits among populations inhabiting similar habitat types. Our results demonstrate that genital evolution can occur during the early stages of speciation-with-gene-flow, potentially as a result of variation in the intensity of sexual conflict among populations. Our results suggest genitalia may contribute to early stages of divergence, and challenge the generality of previously suggested mechanisms of genital evolution in poeciliids.
Female mate preferences do not predict male sexual signals across populations
<p>New species can arise when female preferences and male sexual signals diverge across populations and thereby reduce mating between populations. Under this hypothesized mechanism for speciation, mate preferences and male signals should be correlated, but divergent, across populations. We evaluated this prediction using spadefoot toads (Spea multiplicata). We measured a sexually-selected male signal (call rate) for which female preferences are known to vary across populations in response to hybridization risk. Contrary to expectation, we found no correlation between male call rate and female preferences across populations. We discuss possible mechanisms of this pattern, including the effect of gene flow from heterospecifics on male call rate. Our results suggest that, even when populations vary in mating traits, the independent evolution of female preferences and male sexual signals might impede reproductive isolation between populations. </p>
Extra-pair copulations can insure female blue tits against male infertility
Mating outside the pair-bond occurs frequently in socially monogamous birds, but the benefits that females gain from this behaviour remain debated. One hypothesis is that females engage in extra-pair copulations (EPCs) to ensure that their clutch is fertilised in case their own mate is infertile, but evidence for this idea is scarce. We report on a case of an infertile male blue tit that bred in three successive years with three different females. In the first year, all eggs were sired by an extra-pair male whereas in the second year all eggs were unfertilised and contained no sperm. In the third year, the female produced two clutches that were fertilised by an extra-pair male, but - unlike 'normal' clutches - sperm numbers on the perivitelline membrane decreased rapidly over the laying sequence. Our findings show that blue tit females mated to an infertile male can escape reproductive failure by engaging in EPCs and support previous suggestions that EPCs in blue tits cease after the onset of egg laying.
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Allen Brain Atlas
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