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45 results for “sexual competition”
Asymmetric density-dependent competition does not contribute to the maintenance of sex in a mixed population of sexual and asexual Potamopyrgus antipodarum
<p>Asexual reproduction is expected to have a two-fold reproductive advantage over sexual reproduction, owing to the cost of producing males in sexual subpopulations. The persistence of sexual females thus requires an advantage to sexual reproduction, at least periodically. Here we tested the hypothesis that asexual females are more sensitive to limited resources. Under this idea, fluctuations in the availability of resources (<em>per capita</em>) could periodically favor sexual females when resources become limited. We combined sexual and asexual freshwater snails (<em>Potamopyrgus antipodarum</em>) together in nylon mesh enclosures at three different densities in an outdoor mesocosm. After one month, we counted the brood size of fertile female snails. We found that fecundity declined significantly with increasing density. However, sexual females did not produce more offspring than asexual females at any of the experimental densities. Our results thus suggest that the cost of sexual reproduction in <em>P. antipodarum</em> is not ameliorated by periods of intense resource competition.</p>
Can developmental plasticity shape sexual competition and promote reproductive isolation?
<p>Environmental factors such as dietary nutrients can shape the expression of developmentally plastic sexual traits in many species. However, while there has been extensive research into the developmental plasticity of sexual traits at the individual level, the broader consequences of this variation at the population scale remain poorly understood. Here, we asked whether plastic responses to the developmental environment can shape sexual competition and initiate reproductive isolation between populations. We reared neriid flies, <em>Telostylinus angusticollis</em>,<em> </em>on nutrient-rich and nutrient-poor larval diets, generating adult flies that differed in body size and secondary sexual trait expression. We then investigated sexual competition in experimental populations from each developmental environment, and tested for reproductive isolation between flies from mismatched environments. We found that, compared with poor-diet populations, rich-diet populations exhibited more frequent and escalated male-male combat and more frequent mating and mate-guarding. However, we found no evidence that sexual selection was affected by the developmental environment. Mismatched female-male pairs tended to take longer to mate and rich-diet females often rejected poor-diet males, but mismatched pairs were not less likely to mate within 1 hour or produce viable offspring. Our findings suggest that developmental plasticity could generate dramatic differences in sexual competition between populations, and could contribute to reproductive isolation.</p>
Fig. 2 in Development, reproduction and sexual competitiveness of Conopomorpha sinensis (Lepidoptera: Gracillariidae) gamma-irradiated as pupae and adults
Fig. 2. Mean (± SE) mortality of eggs oviposited by Conopomorpha sinensis females involved in 3 different crosses. The upper curve shows the percentage hatch of eggs from the cross, UF × TM in which males were γ-irradiated as mature pupae with doses ranging egg from 50 and 300 Gy. The middle curve shows the corresponding results from the cross, TF × UM, however females irradiated with 200–300 Gy did not oviposit any eggs. The lower curve shows the corresponding results when both parents were irradiated.
Fig. 1 in Development, reproduction and sexual competitiveness of Conopomorpha sinensis (Lepidoptera: Gracillariidae) gamma-irradiated as pupae and adults
Fig. 1. Fecundity of P generation Conopomorpha sinensis adults that emerged from pupae irradiated at various γ-radiation doses ranging from 50 to 300 Gy. UF = non-irradiated females, TF = treated females, UM = non-irradiated males, TM = treated males. Different letters above bars indicate statistically significant differences within each combination (DMRT, P = 0.05).
Male sexual signaling and expected effects of hatchery-induced sperm competition vary with water depth at which whitefish are caught
<div> <div> <div> <div> <p>Salmonids like whitefish (<em>Coregonus</em> spp.) are often propagated in supportive breeding. Spawners are caught from their spawning locations, their gametes mixed, and the resulting offspring reared in a protected environment before being released into the wild. This procedure can affect sexual selection, for example, by enhancing the importance of sperm competition or by reducing the relevance of sexual signals. While it is often unclear how sperm competitiveness is affected by a male's overall genetic quality, there is accumulating evidence that sexual signals reveal good genes and that mate choice based on such signals can increase offspring viability (Auld et al. 2019). Therefore, supportive breeding may affect the genetic variance and the mean genetic quality of next generations. We sampled whitefish from various locations along a depth gradient to test how male characteristics that are likely to affect sexual selection under natural conditions correlate with characteristics that affect hatchery-induced sperm competition. Whitefish are external fertilizers, and multi-male spawning and hence sperm competition is common under natural conditions. Mate choice is not sufficiently understood but could be based on breeding tubercles. These are small conical structures that grow on scales before the breeding sea- son and fall off shortly afterwards. The size of breeding tubercles varies much among males and has repeatedly been found to correlate positively with offspring viability (Wedekind et al. 2001; Keka ̈la ̈inen et al. 2010). Male dominance is typically depend- ent on body size (Auld et al. 2019) and could also be relevant in whitefish. Body size itself can reflect individual inbreeding coefficients (Su et al. 1996) and be an indicator of heritable genetic quality in small or structured populations (Neff and Pitcher 2008). In another fish with a somewhat comparable mating system, the size of breeding tubercles and male size was not correlated but could both be used to predict male reproductive success under close to natural conditions (Jacob et al. 2009). We study whitefish from Lake Hallwil (Switzerland). This lake has suffered so much from anthropogenic eutrophication that it is being artificially aerated since 1985. Three hatcheries around the lake are likely to have played a key role in maintaining the whitefish population, as concluded also from a recent mark–recapture experiment (Vonlanthen 2015). However, eutrophication combined with possible hybridization in hatcheries can have led to a speciation reversal (Vonlanthen et al. 2012) and may thereby have destroyed any genetic structure linked to water depth. Hatchery protocols now focus on maintaining over-all genetic variance by pooling milt of many males before adding the mix to eggs of multiple females. Milt volume varies among sires, for example, because males often lose milt when being pulled up from deep locations (Figure 1), an effect that likely depends on how much the swim bladder is inflated by the change in pressure. This variance in milt volume is likely to affect the genetic variance that, in combination with the average genetic quality, may then affect the long-term survival of a population. The extent to which hatchery protocols affect genetic quality can be estimated by the correlations between male quality indicators and traits that affect hatchery-induced sperm competition, that is, sperm number, velocity, and longevity (summarized here as "milt potency," see also Supplementary Material). Many breeding protocols are likely to promote genetic quality if male attractiveness or dominance are positively correlated to milt potency. If there are no such correlations or negative ones because of life-history trade-offs, hatchery-induced sperm competition is likely to reduce the average genetic quality in future generations. We sampled fish from various depths and determined their age, size, breeding ornamentation, and milt potency (see methods in the Supplementary Material) to test whether and how different male characteristics affect reproductive success in supportive breeding in a heavily managed population.</p> </div> </div> </div> </div>
Asymmetric density-dependent competition does not contribute to the maintenance of sex in a mixed population of sexual and asexual Potamopyrgus antipodarum
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Male sexual signaling and expected effects of hatchery-induced sperm competition vary with water depth at which whitefish are caught
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Data from: Mating competition among females: testing the distinction between natural and sexual selection in an insect
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Can developmental plasticity shape sexual competition and promote reproductive isolation?
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Female chacma baboons modulate their sexual receptivity in response to male intrasexual competition
<p>Research in social mammals has revealed the complexity of strategies females use in response to female-female reproductive competition and sexual conflict. One point at which competition and conflict manifest acutely is during sexual receptivity, indicated by swellings in some primates. Whether females can adjust their sexual receptivity from cycle to cycle to decrease reproductive competition and sexual conflict in response to social pressures has not been tested. As a first step, this study explores whether sexual receptivity duration is predicted social pressures in wild female chacma baboons (<em>Papio</em> <em>ursinus</em>). Given that female baboons face intense reproductive competition and sexual coercion, we predicted that: females could shorten the duration of their sexual receptive period to reduce female-female aggression and male coercion or increase it to access multiple or their preferred male(s). We quantified 157 ovulatory cycles from 46 wild females living in central Namibia recorded over 15 years. We found no support for our hypothesis; however, our analyses revealed a negative correlation between maximal-swelling duration and group size, a proxy of within-group competition. This study provides further evidence that swelling is costly as well as a testable framework for future investigations of 'cycle length manipulation'.</p>
Eavesdropping micropredators as dynamic limiters of sexual signal elaboration and intrasexual competition
<p>To thoroughly understand the drivers of dynamic signal elaboration requires assessing the direct and indirect effects of naturally interacting factors. Here, we use structural equation modeling (SEM) to test multivariate data from <i>in situ</i> observations of sexual signal production against a model of causal processes hypothesized to drive signal elaboration. We assess direct and indirect effects, and relative impacts, of male-male competition and attacks by eavesdropping frog-biting midges (Diptera: Corethrellidae) on call elaboration of male túngara frogs (<i>Engystomops pustulosus</i>). We find that the intensity of attacks by these micropredator flies drives the extent to which frogs elaborate their calls, likely due to a temporal trade-off between signaling and anti-micropredator defense. Micropredator attacks appear to dynamically limit a male's call rate and complexity and consequently dampen the effects of intrasexual competition. In accounting for naturally interacting drivers of signal elaboration, this study presents a counterpoint to the mechanisms traditionally thought to drive sexual selection in this system. Moreover, the results shed light on the relatively unexamined and potentially influential role of eavesdropping micropredators in the evolution of sexual communication systems.</p>
Data from: Male-male competition causes parasite-mediated sexual selection for local adaptation
<p>Sexual selection has been suggested to accelerate local adaptation and promote evolutionary rescue through several ecological and genetic mechanisms. Condition-dependent sexual selection has mainly been studied in laboratory settings while data from natural populations are lacking. One ecological factor that can cause condition-dependent sexual selection is parasitism. Here, we quantified ectoparasite load (<i>Arrenurus </i>water mites) in a natural population of the common bluetail damselfly (<i>Ischnura elegans</i>) over 15 years. We quantified the strength of sexual selection against parasite load in both sexes and experimentally investigated the mechanisms behind such selection. Then, we investigated how parasite resistance and tolerance changed over time to understand how they might influence population density. Parasites reduced mating success in both sexes, and sexual selection was stronger in males than in females. Experiments show that male-male competition is a strong force causing precopulatory sexual selection against parasite load. Although parasite resistance and male parasite tolerance increased over time, suggestive of increasing local adaptation against parasites, no signal of evolutionary rescue could be found. We suggest that condition-dependent sexual selection facilitates local adaptation against parasites and discuss its effects in evolutionary rescue.</p>
Eavesdropping micropredators as dynamic limiters of sexual signal elaboration and intrasexual competition
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Data from: Male-male competition causes parasite-mediated sexual selection for local adaptation
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Female chacma baboons modulate their sexual receptivity in response to male intrasexual competition
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Habitat deterioration relaxes resource competition and sexual selection in the threespine stickleback
The operation of sexual selection depends on ecological conditions. Thus, changes in environmental conditions because of human activities can alter the strength and direction of sexual selection, with implications for evolutionary trajectories and the viability of populations. We show that aquatic algal blooms can relax the operation of sexual selection by influencing which males are available to attract females. This is by influencing the ability of males to maintain a resource needed in mate attraction. When we exposed two competing threespine stickleback males (Gasterosteus aculeatus), whose attractiveness to females was known, to either clear or algal-turbid water, nest abandonment was more common in clear water, and it was usually the unattractive male that abandoned his nest. In turbid water, on the other hand, nest abandonments were less common and when they occurred, the probability increased that the attractive male abandoned his nest, and that the unattractive male subsequently occupied it. This change in the composition of nesting males increased the mating success of unattractive males. Thus, our results reveal a new mechanism through which habitat deterioration can influence sexual selection, by altering success in the competition for a resource critical in mate attraction, a territory with a nest in this case. This could be a common mechanism, considering the prevalence of resource competition in mate choice systems. On a broader level, our results emphasise the importance of considering the impact of environmental changes on the outcome of resource competition when investigating the influence that environmental disturbances have on the operation of sexual selection and thereby on evolutionary processes and population dynamics.
Data from: Multivariate sexual selection on ejaculate traits under sperm competition
The widespread prevalence of sperm competition means that ejaculates face intense sexual selection. However, prior investigations of sexual selection on gametes have been hampered by two difficulties: (1) deriving estimates of relative fitness from sperm competition trials that are comparable across rival male and female genotypes; and (2) obtaining measures of competitive fertilization success that are not confounded by post-zygotic effects. Here, we exploit the experimental tractability of a broadcast spawning marine invertebrate to overcome these challenges and characterise multivariate sexual selection on sperm traits when multiple ejaculates compete. In multi-male spawning events, we tracked real-time success of sperm using fluorescent tags that are visible inside fertilized eggs. We then used multivariate selection analyses to identify patterns of linear and non-linear sexual selection on multiple sperm morphology and motility traits. Specifically, we found non-linear selection against divergent combinations of sperm length, velocity and swimming path linearity. These patterns likely reflect the way different swimming strategies allow sperm to locate and track eggs. Our results demonstrate that there are overall patterns of selection on ejaculates across a biologically realistic range of ejaculate-ejaculate and ejaculate-female interactions; therefore, there is the potential for adaptive evolution of ejaculate traits under sperm competition.
Data from: Sisters' curse: sexually antagonistic effects constrain the spread of a mitochondrial haplogroup superior in sperm competition
Maternal inheritance of mitochondria creates a sex-specific selective sieve with implications for male longevity, disease susceptibility and infertility. Because males are an evolutionary dead end for mitochondria, mitochondrial mutations that are harmful or beneficial to males but not females cannot respond directly to selection. Although the importance of this male/female asymmetry in evolutionary response depends on the extent to which mitochondrial mutations exert antagonistic effects on male and female fitness, few studies have documented sex-specific selection acting on mitochondria. Here, we exploited the discovery of two highly divergent mitochondrial haplogroups (A and B2) in central Panamanian populations of the pseudoscorpion Cordylochernes scorpioides. Next-generation sequencing and phylogenetic analyses suggest that selection on the ND4 and ND4L mitochondrial genes may partially explain sexually antagonistic mitochondrial effects on reproduction. Males carrying the rare B2 mitochondrial haplogroup enjoy a marked advantage in sperm competition, but B2 females are significantly less sexually receptive at second mating than A females. This reduced propensity for polyandry is likely to significantly reduce female lifetime reproductive success, thereby limiting the spread of the male beneficial B2 haplogroup. Our findings suggest that maternal inheritance of mitochondria and sexually antagonistic selection can constrain male adaptation and sexual selection in nature.
Supporting Information - An experimental assessment of competitive interactions between sexual and apomictic fern gametophytes using Easy Leaf Area
<p>Supporting Information for the paper titled <strong>An experimental assessment of competitive interactions between sexual and apomictic fern gametophytes using Easy Leaf Area</strong> published in Applications in Plant Sciences.</p>
Rapid evolution of ecological sexual dimorphism driven by resource competition
<p>Sex differences in ecologically-important traits are common in animals and plants, and prompted Darwin to first propose an ecological cause of sexual dimorphism. Despite theoretical plausibility and Darwin's original notion, a role for ecological resource competition in the evolution of sexual dimorphism has never been directly demonstrated and remains controversial. I used experimental evolution in <em>Drosophila melanogaster</em> to test the hypothesis that resource competition can drive the evolution of sex differences in diet. Following just three generations of adaptation, offspring from flies evolved in low-resource, high-competition environments show elevated sexual dimorphism in diet preference compared to both the ancestor and populations evolved on high resource availability. This increased sexual dimorphism was the result of divergence in male sucrose intake and female yeast intake consistent with the differential nutritional requirements of the sexes. These results provide the first real-time direct evidence for evolution of sexual dimorphism driven by resource competition.</p>
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