Transient polymorphisms in parental care strategies drive divergence of sex roles

The parental roles of males and females differ considerably between and within species. By means of individual-based evolutionary simulations, we strive to explain this diversity. We show that the conflict between the sexes creates a sex bias (towards maternal or paternal care), even if the two sexes are initially identical. When including sexual selection, there are two outcomes: either female mate choice and maternal care or no mate choice and paternal care. Interestingly, the care pattern drives sexual selection and not vice versa. Longer-term simulations exhibit rapid switches between alternative parental care patterns, even in constant environments. Hence, the evolutionary lability of sex roles observed in phylogenetic studies is not necessarily caused by external changes. Overall, our findings are in striking contrast to the predictions of mathematical models. We show that the discrepancies are caused by transient within-sex polymorphisms in parental strategies, a factor largely neglected in current sex-role theory. Animals differ remarkably in how parental care is distributed between the male and female parent. Here, the authors use evolutionary simulations to reveal that sex differences in care readily emerge in a characteristic manner that is not captured by current sex role theory.

Automated summary

The study examines the diversity in parental roles between and within species. By using individual-based evolutionary simulations, the authors find that differences in care between males and females can arise from conflicts between the sexes and sexual selection. The study reveals that the care pattern drives sexual selection, and rapid switches between parental care patterns can occur even in constant environments. The findings challenge the predictions of mathematical models and highlight the importance of transient within-sex polymorphisms in parental strategies.