Multiple Paternity, Mate Choice and Siring Success During Drought: Implications for a Semelparous Marsupial

Multiple paternity in litters and a female’s choice of mate can significantly influence siring success and the success and survival of offspring. In captive agile antechinus (Antechinus agilis), a small, carnivorous marsupial that exhibits obligate semelparity, females choose to mate with multiple males and mate choice is profoundly influenced by genetic dissimilarity between mates, not male size. However, female mate choice has not been examined in wild agile antechinus. Our study encompassed one year in which the operational sex ratio was at parity and a second in which the ratio was female biased, and animal weight, survival and litter size were significantly decreased due to severe drought conditions. Using genetic data from 204 pouch young, we show that genetically dissimilar males sired a higher proportion of young when the sex ratio was at parity, but there was no influence of relatedness on siring success during drought conditions. Larger males sired a higher proportion of young in both years, suggesting that female choice may be partially over-ridden by male behaviour. We highlight concerns for semelparous marsupials during increasingly frequent environmental disruptions, including drought, which could influence mate choice behaviours, reproductive success, genetic health and population survival.