Jennions et al. introduce the different kinds of sex ratio and their biology.

The observed sex ratio is nearly one half in many animals including humans. Fisher explained that the 50/50 sex ratio is optimal. However, the 50/50 sex ratio seems highly unstable because a slight deviation from 50/50 changes the optimal ratio to the opposite extremes; zero or unity. Thus sex ratio should be fluctuating wildly around 50/50. In contrast, the observed 50/50 sex ratios in wild po...

Post-mating, sexual interactions of opposite sexes differ considerably in different organisms. Post-mating interactions such as re-mating behavior and male harassment can affect the fitness of both sexes. Echinothrips americanus is a new insect pest in Mainland China, and little is known about its post-mating interactions. In this study, we observed re-mating frequency and male harassment frequ...

One of the better-studied sex ratio theories is local mate competition (LMC) theory, first developed by Hamilton in 1967 (for reviews see Charnov, 1982; Waage, 1986; King, 1987). LMC models assume a subdivided population structure with emergence and then random mating taking place within local patches followed by female dispersal to new patches to lay offspring. Under these conditions, offsprin...

Many social behaviors arc conditional, but behavioral comparisons between populations do not normally distinguish genetic and environmental causation. As a result, the opportunity to test predictions about the evolution of strategic conditionality (genotype x environment interaction) is lost. We apply these concepts in an examination of how interpopulation differences in mean and variance of se...

Interspecific mating can cause severe fitness costs due to the fact that hybrids are often non-viable or less fit. Thus, theory predicts the selection of traits that lessen reproductive interactions between closely related sympatric species. Males of the parasitic wasp Nasonia vitripennis differ from all other Nasonia species by an additional sex pheromone component, but the ecological selectiv...

When faced with risky decisions, people typically choose to diversify their choices by allocating resources across a variety of options and thus avoid putting “all their eggs in one basket.” The current research revealed that this tendency is reversed when people face an important cue to mating-related risk: skew in the operational sex ratio, or the ratio of men to women in the local environmen...

Sex allocation theory offers excellent opportunities for studying the precision of adaptation. One of the best-supported areas in the field of sex allocation is Hamilton's theory of local mate competition, which predicts female-biased offspring sex ratios when populations are structured such that mating takes place locally before females disperse. As predicted by local mate competition theory, ...