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A female (left) and a male (right) red-fronted lemur with an infant (center). Photo Credit: Louise Peckre |
How picky should females and males be when they choose a mate? How fiercely should they compete for mates? And how much should they engage in raising their offspring? The answers to these questions largely depend on the ratio of adult females to males in the social group, population or species. This is the conclusion of a review by a scientific team with the participation of the German Primate Center – Leibniz Institute for Primate Research (DPZ), the Max Planck Institute for Biological Intelligence, in foundation, and the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW). The paper is published in the journal Biological Reviews.
In species with separate sexes, females and males often differ in their morphology, physiology and behavior. Such sex-specific adaptations imply differences between females and males in the degree of mate competition, mate choice and parental care. Empirical research showed that females generally tend to be choosier than males about whom to mate with, and males are more likely than females to compete for mating opportunities. This pattern is often referred to as “conventional” sex roles. But the opposite pattern (“reversed” sex roles) also exists and there generally is a lot of variation in sex roles both between and within species. How can this surprisingly large variation in sex roles be explained? The team led by Peter Kappeler from the German Primate Center now reviewed the sex roles literature in animals and found that the ratio of adult males to females in a population likely is a strong evolutionary driver of sex roles. The scientific paper also identifies unanswered questions and proposes research that can lead to a better understanding of sexual selection and the evolution of sex roles.