Alternative reproductive tactics in female striped mice: Solitary breeders have lower corticosterone levels than communal breeders

International audienceAlternative reproductive tactics (ARTs),where members of the same sex and population show distinct reproductivephenotypes governed by decision-rules, have been well-documented in males of many species, but are lesswell understood in females. The relative plasticity hypothesis (RPH) predicts that switches between plastic ARTsare mediated by changes in steroid hormones. This has receivedmuch support in males, but little is known aboutthe endocrine control of female ARTs. Here, using a free-living population of African striped mice (Rhabdomyspumilio) over five breeding seasons, we tested whether females following different tactics differed in corticosteroneand testosterone levels, as reported for male striped mice using ARTs, and in progesterone and oestrogen,which are important in female reproduction. Female striped mice employ three ARTs: communal breeders givebirth in a shared nest and provide alloparental care, returners leave the group temporarily to give birth, and solitarybreeders leave to give birth and do not return. We expected communal breeders and returners to havehigher corticosterone, owing to the social stress of group-living, and lower testosterone than solitary breeders,which must defend territories alone. Solitary breeders had lower corticosterone than returners and communalbreeders, as predicted, but testosterone and progesterone did not differ between ARTs. Oestrogen levels werehigher in returners (measured before leaving the group) than in communal and solitary breeders, consistentwith a modulatory role. Our study demonstrates hormonal differences between females following (or about tofollow) different tactics, and provides the first support for the RPH in females