Search

Within-population variation in ageing remains poorly understood. In males, condition-dependent investment in secondary sexual traits may incur costs that limit ability to invest in somatic maintenance. Moreover, males often express morphological and behavioral secondary sexual traits simultaneously, but the relative effects on ageing of investment in these traits remain unclear. We investigated the condition dependence of male life history in the neriid fly Telostylinus angusticollis. Using a fully factorial design, we manipulated male early-life condition by varying nutrient content of the larval diet and, subsequently, manipulated opportunity for adult males to interact with rival males. We found that high-condition males developed more quickly and reached their reproductive peak earlier in life, but also experienced faster reproductive ageing and died sooner than low-condition males. By contrast, interactions with rival males reduced male lifespan but did not affect male reproductive ageing. High-condition in early life is therefore associated with rapid ageing in T. angusticollis males, even in the absence of damaging male-male interactions. Our results show that abundant resources during the juvenile phase are used to expedite growth and development and enhance early-life reproductive performance at the expense of late-life performance and survival, demonstrating a clear link between male condition and ageing. [ABSTRACT FROM AUTHOR]

Background: Intralocus sexual conflict, arising from selection for different alleles at the same locus in males and females, imposes a constraint on sex-specific adaptation. Intralocus sexual conflict can be alleviated by the evolution of sex-limited genetic architectures and phenotypic expression, but pleiotropic constraints may hinder this process. Here, we explored putative intralocus sexual conflict and genetic (co)variance in a poorly understood behavior with near male-limited expression. Same-sex sexual behaviors (SSBs) generally do not conform to classic evolutionary models of adaptation but are common in male animals and have been hypothesized to result from perception errors and selection for high male mating rates. However, perspectives incorporating sex-specific selection on genes shared by males and females to explain the expression and evolution of SSBs have largely been neglected. Results: We performed two parallel sex-limited artificial selection experiments on SSB in male and female seed beetles, followed by sex-specific assays of locomotor activity and male sex recognition (two traits hypothesized to be functionally related to SSB) and adult reproductive success (allowing us to assess fitness consequences of genetic variance in SSB and its correlated components). Our experiments reveal both shared and sex-limited genetic variance for SSB. Strikingly, genetically correlated responses in locomotor activity and male sex-recognition were associated with sexually antagonistic fitness effects, but these effects differed qualitatively between male and female selection lines, implicating intralocus sexual conflict at both male- and female-specific genetic components underlying SSB. Conclusions: Our study provides experimental support for the hypothesis that widespread pleiotropy generates pervasive intralocus sexual conflict governing the expression of SSBs, suggesting that SSB in one sex can occur due to the expression of genes that carry benefits in the other sex. [ABSTRACT FROM AUTHOR]

Why do the two sexes have different lifespans and rates of aging? Two hypotheses based on asymmetric inheritance of sex chromosomes ('unguarded X') or mitochondrial genomes ('mother's curse') explain sex differences in lifespan as sex-specific maladaptation leading to increased mortality in the shorter-lived sex. While asymmetric inheritance hypotheses equate long life with high fitness, considerable empirical evidence suggests that sexes resolve the fundamental tradeoff between reproduction and survival differently resulting in sex-specific optima for lifespan. However, selection for sex-specific values in life-history traits is constrained by intersexual genetic correlations resulting in intra-locus sexual conflict over optimal lifespan. The available data suggest that the evolution of sexual dimorphism only partially resolves these conflicts. Sexual conflict over optimal trait values, which has been demonstrated in model organisms and in humans, is likely to play a key role in shaping the evolution of lifespan, as well as in maintaining genetic variation for sex-specific diseases. [ABSTRACT FROM AUTHOR]

1. Sexual selection is a powerful evolutionary force that is hypothesised to play an important role in the evolution of lifespan. Here we test for the potential contribution of sexual selection to the rapid evolution of male lifespan in replicated laboratory populations of the seed beetle, Callosobruchus maculatus. 2. For 35 generations, newly hatched virgin male beetles from eight different populations were allowed to mate for 24 h and then discarded. Sexual selection was removed in half of these populations by enforcing random monogamy. 3. Classic theory predicts that because of sexual competition, males from sexually selected lines would have higher age-specific mortality rates and shorter lifespan than males from monogamous lines. 4. Alternatively, condition-dependent sexual selection may also favour genes that have positive pleiotropic effects on lifespan and ageing. 5. Males from all eight populations evolved shorter lifespans compared with the source population. However, there was no difference in lifespan between males from populations with or without sexual selection. Thus, sexual selection did not contribute to the evolution of male lifespan despite the fact that such evolution did occur in our study populations. [ABSTRACT FROM AUTHOR]

Evolutionary theories of aging predict that fitness-related traits, including reproductive performance, will senesce because the strength of selection declines with age. Sexual selection theory predicts, however, that male reproductive performance (especially sexual advertisement) will increase with age. In both bodies of theory, diet should mediate age-dependent changes in reproductive performance. In this study, we show that the sexes exhibit dramatic, qualitative differences in age-dependent reproductive performance trajectories and patterns of reproductive ageing in the cricket Teleogryllus commodus. In females, fecundity peaked early in adulthood and then declined. In contrast, male sexual advertisement increased across the natural lifespan and only declined well beyond the maximum field lifespan. These sex differences were robust to deviations from sex-specific dietary requirements. Our results demonstrate that sexual selection can be at least as important as sex-dependent mortality in shaping the signal of reproductive ageing. [ABSTRACT FROM AUTHOR]

Males in different taxa are likely to suffer from a reduction in the quantity and/or quality of their sperm with age. This predicts age-related direct and indirect effects on female fitness. Hence, females may be selected to avoid matings with old males, or to employ alternative mating tactics, such as polyandry, to avoid fertilization by sperm of older males. In contrast, ‘viability indicator’ models of mate choice predict female preference for old males that have proven their survival ability and signal more reliably. We used a polygamous seed beetle, Callosobruchus maculatus, to test for the effects of male age on male mating success and examine the relationship between male age and female fitness, measured as female life span, lifetime fecundity, hatching success of eggs, larval development rate and egg-to-adult survival of offspring. Furthermore, we tested the hypothesis that polyandry may protect females against low numbers of functional sperm produced by old males. We report, contrary to previous findings, that male mating success indeed decreases with male age in this species. However, mating with older males did not in any way compromise female fitness and, consequently, we found no support for the idea that polyandry helps females reduce any costs of mating with older males. [Copyright &y& Elsevier]

1. Sexual conflict, which results from the divergence of genetic interests between males and females, is predicted to affect multiple behavioural, physiological, and morphological traits. 2. Sexual conflict over mating may interact with population density to produce predictable changes in resource allocation into inter-sexual armament. 3. In the spider Stegodyphus lineatus, males fight with females over re-mating. The outcome of the fight is influenced by the cephalothorax size of the contestants. The investment in armament – the cephalothorax, may be traded-off against investment in abdomen, which is a trait that affects survival and fecundity. Pay-offs may depend on population density. Both sexes are expected to adjust resource allocation into different body parts accordingly. 4. Males had increased cephalothorax/body size ratio in low densities where probability of finding another receptive female is low and females had increased cephalothorax/body size ratio in high densities where cumulative costs of multiple mating are high. 5. The results support the theoretical conjecture that population density affects resource allocation into inter-sexual armament and call for further research on the interaction between sexual selection and population density. [ABSTRACT FROM AUTHOR]

Female-biased sexual size dimorphism (SSD) is found in many organisms yet is poorly understood. Spiders in general, and web-building species in particular, typically have strongly female-biased SSD. We investigated the causes of SSD in the web-building spider Stegodyphus lineatus. Females are slightly, but significantly, larger than males. Large females are more fecund but the selection pressures on male body size are not clear. Males were introduced on to the webs of virgin and mated females and we also conducted competition experiments between males. Large males did not have longer copulations, nor did they mate more successfully with virgin females than small males did; however, they were more successful with previously mated females and remated more often. They also won more fights, and were more successful at obtaining prey from the female''s web. Indiscriminate mating by virgin females, however, conferred a fitness advantage on early maturing males. We suggest that the female''s mating strategy selects for protandry, which results in female-biased SSD, despite the selection for large body size in males. Indiscriminate mating by females and a trade-off between time to maturation and male body size may be important in understanding the evolution of female-biased SSD. [Copyright &y& Elsevier]

Same-sex sexual behaviour is widespread across taxa and is particularly common in insects, in which up to 50% of copulation attempts by males are directed towards other males in some species. Research effort has focused on male–male same-sex behaviour and the prevailing theory is that benefits of high mating rate combined with poor sex discrimination explain the high incidence of male–male mounting. However, the evolution of female–female mounting is more enigmatic, since females typically do not mount males in order to mate. Using a full-sib design, we found an intersexual correlation for same-sex mounting in the beetle Callosobruchus maculatus. Variation in male–male mounting across families explained over 20% of variation in female–female mounting. Moreover, we found no evidence that same-sex behaviour was related to general activity level in either sex or carried a fitness cost to females. Taken together, our results suggest that female–female mounting is a relatively low-cost behaviour that may be maintained in the population via selection on males. [ABSTRACT FROM AUTHOR]