One of nature’s biggest mysteries is why some females mate with multiple males (polyandry) despite the risk of disease transmission, potential injury and even increased predation risk. In externally fertilizing animals, including some species of fish and frogs, females can mate with multiple males at the same time (simultaneous polyandry).
Scientists investigated whether simultaneous polyandry influences offspring fitness in a wild population of the African Grey Foam Nest Treefrog (Chiromantis xerampelina
). Simultaneous polyandry in this frog is the most extreme reported for any vertebrate, with more than 90% of females mating with 10 or more males during the deposition of a single clutch. They compared growth (using age and size at metamorphosis as proxies) and survival of offspring produced by females that naturally mated with either one male (monandrous females) or 10–12 males (polyandrous females). Polyandry did not influence size or age at metamorphosis, but offspring from polyandrous matings had significantly higher mean survival.
Their findings implicate a genetic benefit to females mating with multiple males, and suggest that females are advantaged by mating promiscuously.