Incest-avoiding Females Cause Males To Leave

Main Category: Psychology / Psychiatry
Also Included In: Veterinary
Article Date: 16 Aug 2007 - 0:00 PDT

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Animals generally avoid inbreeding because it is genetically hazardous. They can either do this by moving away from home or, like humans, by learning who their relatives are and not mating with them. In most mammals, the young males move away and the females stay, resulting in a low level of inbreeding. But why is it the males that move away, given that the females invest much more in raising their offspring and should therefore have a greater interest in avoiding inbreeding?

Research on spotted hyenas published in Nature this week by an international team of scientists from the Leibniz Institute for Zoo and Wildlife Research (IZW) in Berlin, Germany, and the University of Sheffield, UK, now shows that the reason most males move from their natal group is because of female mate-choice the rules females use when choosing which of many male group members will sire their offspring. Young females prefer to mate with "new arrivals" in a group males born into the group or males that immigrated into the group after the female was born because by doing so they avoid breeding with their father and their older brothers. Females are unlikely to know who their father is because like most male mammals male hyenas do not contribute to the rearing of their offspring and females mate promiscuously.

Older females also apply this rule and in addition prefer males that have built friendly relationships with them for several years. These age-related mate preferences of females (assortative mating) influence where males choose to initiate their reproductive careers because ultimately they determine a male's reproductive success. The results of this study demonstrate that males mostly start their reproductive careers in groups with the highest number of young females and that the males that choose groups containing the highest number of young females sire the highest number of offspring in the long term. "Long-lived males that selected the correct group at the start of their reproductive career had access to a high number of females for many years and sired far more offspring than other males", says Dr Oliver Höner from the IZW. Most males disperse because a higher number of young females usually occurs elsewhere, rather than in the group in which the male was raised. Dr Höner adds: "The results of the study were only possible because we could monitor the decision by males on where to start their reproductive career in all eight resident hyena groups on the floor of the Ngorongoro Crater and we could genetically determine paternity for most offspring produced in a 10-year monitoring period."

This is the first time it has been shown in a mammalian species that the males that respond best to female mate preferences and as a result in most cases move from their natal group do pass on more of their genes to future generations, and that the system is driven by females using very simple rules, which are enough to prevent them from mating incestuously.

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