The adult sex ratio (ASR; the ratio of adult males to adult females in a population) is a fundamental variable in demography and population biology. The ASR is predicted to play a major role in influencing reproductive behavior such as mating competition, sex roles and parental care across all animals, including humans. The ASR is therefore likely to help explain variation in mating systems (i.e. who mates with whom and when) both among species and among populations. Indeed, in humans, recent (but often rather preliminary) studies show that the ASR can be used to predict mate choice, economic behavior, divorce rates, extra-marital affairs and levels of rape and violence. Therefore, determining the causes and implications of ASR variations in wild populations could provide important comparative insights to yield a more comprehensive understanding of the evolutionary processes affecting the social behavior of both animals and humans.
The ASR varies widely among species, and the few available studies suggest that variations in ASRs impact behavior, ecologies and life histories. In this Wiko Focus Group project we propose to carry out a comprehensive assessment of adult sex ratio variation using vertebrates as model organisms. We seek to establish what causes ASR variation in the five major vertebrate taxa (i.e., mammals, birds, reptiles, amphibians, fishes), and we will seek to explore how ASR variation is related to variation across species (or populations) in social behavior, sex roles and mating systems. Our main focus is to find broad scale patterns that cut across the many million years of independent vertebrate evolution in these five groups.
Tamás Székely und Peter M. Kappeler