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Female hymenoptera are renowned for their ability to adjust offspring sex ratio to local mate competition. When two females share a patch, they frequently produce clutches that differ in size, the female with the larger clutch optimally producing a more female‐biased sex ratio and vice versa. Females can base their sex allocation on their own clutch size only (“self‐knowledge”) or on both females’...
Sex‐allocation theory predicts that females in good condition should preferentially produce offspring of the sex that benefits the most from an increase in maternal investment. However, it is generally assumed that the condition of the sire has little effect on progeny sex ratio, particularly in species that lack parental care. We used a controlled breeding experiment and molecular paternity analyses...
Sex allocation theory has been remarkably successful at explaining the prevalence of even sex ratios in natural populations and at identifying specific conditions that can result in biased sex ratios. Much of this theory focuses on parental sex determination (SD) strategies. Here, we consider instead the evolutionary causes and consequences of mixed offspring SD strategies, in which the genotype of...
Sex allocation in hermaphrodites can be affected by spatial and temporal variation in resources, especially in plants where size‐dependent gender modification is commonplace. The evolution of sex allocation will depend on the relative importance of genetic and environmental factors governing patterns of investment in female and male function. In wind‐pollinated plants, theoretical models predict a...
Despite decades of research, whether vertebrates can and do adaptively adjust the sex ratio of their offspring is still highly debated. However, this may have resulted from the failure of empirical tests to identify large and predictable fitness returns to females from strategic adjustment. Here, we test the effect of diet quality and maternal condition on facultative sex ratio adjustment in the color...
The sex ratio behavior of parasitoid wasps in the genus Melittobia is scandalous. In contrast to the prediction of Hamilton's local mate competition theory, and the behavior of numerous other species, their extremely female‐biased sex ratios (1–5% males) change little in response to the number of females that lay eggs on a patch. We examined the mating structure and fitness consequences of adjusting...
The taxonomically widespread nature of polyandry remains a puzzle. Much of the empirical work regarding the costs and benefits of multiple mating to females has, for obvious reasons, relied on species that are already highly polyandrous. However, this makes it difficult to separate the processes that maintain the current level of polyandry from the processes that facilitate its expression and initiated...
Despite keen interest in extra‐pair mating in birds, its adaptive significance remains unresolved. Here, we use a multi‐year dataset to test whether traits of a female's social mate influence her propensity to produce extra‐pair offspring in a population of house wrens, and whether producing extra‐pair young has consequences for a female's fitness through effects on offspring survival. Females were...
Basic models of mating‐system evolution predict that hermaphroditic organisms should mostly either cross‐fertilize, or self‐fertilize, due to self‐reinforcing coevolution of inbreeding depression and outcrossing rates. However transitions between mating systems occur. A plausible scenario for such transitions assumes that a decrease in pollinator or mate availability temporarily constrains outcrossing...
Sex allocation theory predicts that parents are selected to bias their progeny sex ratio (SR) toward the sex that will benefit the most from parental quality. Because parental quality may differentially affect survival of sons and daughters, a pivotal test of the adaptive value of SR adjustment is whether parents overproduce offspring of the sex that accrues larger fitness advantages from high parental...
Sex allocation theory predicts that simultaneous hermaphrodites evolve to an evolutionary stable resource allocation, whereby any increase in investment to male reproduction leads to a disproportionate cost on female reproduction and vice versa. However, empirical evidence for sexual trade‐offs in hermaphroditic animals is still limited. Here, we tested how male and female reproductive traits evolved...
Models of sex‐allocation conflict are central to evolutionary biology but have mostly assumed static decisions, where resource allocation strategies are constant over colony lifespan. Here, we develop a model to study how the evolution of dynamic resource allocation strategies is affected by the queen‐worker conflict in annual eusocial insects. We demonstrate that the time of dispersal of sexuals...
Hamilton's idea that haplodiploidy favors the evolution of altruism—the haplodiploidy hypothesis—relies on the relatedness asymmetry between the sexes caused by the sex‐specific ploidies. Theoretical work on the consequences of relatedness asymmetries has significantly improved our understanding of sex allocation and intracolony conflicts, but the importance of haplodiploidy for the evolution of altruism...
In hermaphrodites, the allocation of resources to each sex function can influence fitness through mating success. A prediction that arises from sex allocation theory is that in wind‐pollinated plants, male fitness should increase linearly with investment of resources into male function but there have been few empirical tests of this prediction. In a field experiment, we experimentally manipulated...
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