Hormonal lockdown : how mole-rat societies enforce infertility in helpers

Abstract

Reproductive suppression is a defining feature of cooperative breeding, yet the hormonal mechanisms regulating infertility in non-breeding individuals remain poorly understood. This study examines associations between circulating prolactin (PRL) and faecal metabolites of androgens (fAM), glucocorticoids (fGCM), and progesterone (fPM) in relation to socially induced infertility in two closely related cooperatively breeding mole-rat subspecies: the highveld (Cryptomys hottentotus pretoriae) and Natal mole-rat (C. hottentotus natalensis). Our results reveal a fundamental dichotomy in reproductive suppression strategies. Highveld mole-rats exhibited seasonally elevated circulating PRL in non-breeders during the dry season, coinciding with reduced pituitary responsiveness to exogenous gonadotropin-releasing hormone (GnRH) and lower gonadal steroid metabolites. These associations are consistent with PRL involvement in physiological suppression of the hypothalamic-pituitary-gonadal (HPG) axis, but causality cannot currently be inferred. In stark contrast, Natal mole-rats showed relatively low and stable PRL levels across reproductive groups and seasons, with breeders exhibiting higher androgen and progesterone metabolites compared to non-breeders, a pattern consistent with behavioural suppression through incest avoidance, aggression or social dominance. These findings highlight the adaptive flexibility of cooperatively breeding systems and provide new insights into the hormonal architecture of reproductive suppression. Although the present findings do not establish causality, they delineate key hormonal and behavioural pathways that warrant future investigation.