Female reproduction in alpine marmots (Marmota marmota) [Reproduction ds femelles chez la marmotte alpine]

Résumé

We studied female Alpine marmots over 14 years in the Berchtesgaden National Park, Germany, and investigated reproduction in relation to social interactions and corticosteroid levels. Animals were captured constinuously with live-traps and maked individuals were constantly observed during the active season from April (at emergence from hibernation) to October (at immergence to hibernation). Beside body mass and size, we measured concentrations of plasma estradiol, progesterone, and corticosteroids using enzyme immunoassays. Alpine marmots lived in family groups which consisted of one dominant pair and several subordinate members. There was conformity between females of different social status in main factor affecting mammalian reproduction, but only dominant females produced weaned young. Although subordinate females copulated with males and start pregnancies, none of them reproduced successfully. During early gestation dominant females initiated and won agonistic interactions with subordinate females. As a consequence, subordinate females had higher levels of plasma corticosteroids during this time. Abortion and resorption of embryos are well known in marmots. These data suggest that all adult females within a family group ovulated irrespectively of their social rank, but dominant females were able to monopolise reproduction by social stress against subordinates. Dominant females themselves could be prevented to produced young in groups with several subordinate females and after territory take-overs by males.