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Relationship between sexual selection and mating outside a social group

  • Photo : Purabi Deshpande / Research Matters
    Photo : Purabi Deshpande / Research Matters

In the study of evolutionary biology, a lot of importance is given to trade offs in the survival of organisms. Questions like when should a predator hunt or when should it conserve energy, when should a prey remain solitary and when should it be social, are often always answered by weighing in the tradeoffs. Another important aspect of an organism’s life is passing on its genes and hence, many tradeoffs come into play when studying different mating systems seen in nature.

On one extreme is monogamy in which organisms mate with one partner for life; a system is seen in many bird species, like albatrosses and penguins. On the other end of the spectrum is polygamy, in which one organism can have many partners throughout its life. Different kinds of polygamy are observed in the animal kingdom depending on whether the male or the female of a species has multiple partners. A system where one male mates with multiple females is called polygyny,as  seen in gorillas and territorial birds like warblers, to name a few.

In their recent study, the researchers have explored if males engaging in ‘extra group paternity’ are preferred by females of a species in particular social breeding systems. Extra group paternity refers to the males who father offspring outside their social breeding group. Conventionally, it is believed that extra group paternity increases the male reproductive skew as  a male can pass on more of his genes to the next generation. This scenario leads to an increased competition among the males of a species, allowing females to choose to mate with the ‘winners’ of this competition. But this relationship is not understood across different types of animals.

Looking at 27 mammals across 7 orders, the researchers found that extra group paternity appears to increase the potential for sexual selection but only when the degree of social polygyny is relatively low. The results mean that in monogamous mating systems or mating systems where a male has a small group of partners, it is in the male’s evolutionary interest to mate outside his social group. But, as the number of females in a polygynous group increase, the benefits a male can have by mating outside the social group decreases. The study sheds light on the intricacies of trade-offs in mating systems, bringing us a step closer to understand how and why animals living in social groups breed the way they do.