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Canberra (Australia), 09 November: Female mammals may take multiple partners because it increases the fitness of their offspring, a field study of Australian marsupials suggests in this week’s Nature.

Researchers have struggled to understand why females mate with multiple males when egg production is costly and ‘sleeping around’ raises the risk of disease and injury. Invertebrate studies suggest that the strategy yields genetic benefits and can increase offspring survival, but the reasons why were unclear and the same effects had yet to be proved for mammals in the wild.

Diana O. Fisher and colleagues studied the practice in the brown antechinus (Antechinus stuartii), a carnivorous mouse-like marsupial. Most females breed only once in their lifetime, mating multiply then giving birth synchronously. Although the paternity of offspring can be tested from a very young age, fathers die before any offspring are born, and so childcare falls to the females. It makes sense then that females should invest maximally in a litter (which eliminates selective female investment as an explanation for why sleeping around is good). And polyandry, the team found, leads to better quality offspring as a result of sperm competition.

(ResearchSEA)