Male-caused failure of female reproduction and its adaptive value in alpine marmots (Marmota marmota)

Abstract

We studied reproductive performance of free-living alpine marmots (Marmota marmota) for 14 years in the National Park of Berchtesgaden, Germany. Female reproduction was influenced by body condition and social factors. Reproduction depleted fat reserves, and only females emerging from hibernation with sufficient body mass were able to reproduce successfully. Marmots lived in social groups in territories defended by a dominant male and female. Subordinate females never reproduced, regardless of body mass. Territory takeovers by males impaired reproduction of dominant females, but only if the takeover occurred after the mating period. Reproductive failures occurred despite clear signs of pregnancy such enlarged nipples or late molt. Decreasing progesterone levels after the mating period and the lack of evidence for direct infanticide by new territorial males suggest a block of pregnancy as a likely explanation for reproductive failures in groups with male takeovers during gestation. Rendering female reproduction impossible increased future reproductive success of new territory owners. Nonparous females saved the energetic cost of maternal investment and thus emerged with higher body mass in the following spring. In line with this, females failing to wean young had higher reproductive success in the subsequent year.