Non-Invasive Quantification of Faecal and Urine Reproductive Hormone Metabolites in the Naked Mole-Rat (Heterocephalus glaber)

SIMPLE SUMMARY: The naked mole-rat occurs in colonies with a distinct dominance hierarchy which includes a dominant breeding female, from one to three breeding males, and a number of subordinate individuals that are physiologically blocked from reproducing by the breeders but can reproduce if removed from the colony. Due to their small size, blood sampling is limiting, and measuring reproductive hormones in faeces or urine is considered an alternative method of quantification. Thus, we aimed to validate enzyme immunoassays (EIAs) for measuring androgens and progestogens or their metabolites in naked mole-rat urine and faeces. We administered gonadotrophin-releasing hormone (GnRH), a molecule which stimulates the release of reproductive hormones, and a saline control to twelve (six males and six females) naked mole-rats. The results revealed that urine is possibly not ideal for measuring reproductive hormones in naked mole-rats as no signal administration was detected in the matrix. A 5α-Progesterone EIA and an Epiandrosterone EIA were identified as suitable for quantifying faecal progesterone and androgen metabolites in male and female naked mole-rats. In addition, differences in how the animals responded to a GnRH challenge suggest that some individuals of both sexes are still incapable of reproducing even after being separated from the colony and the breeding female. ABSTRACT: The naked mole-rat (Heterocephalus glaber) occurs in colonies with a distinct dominance hierarchy, including one dominant, breeding female (the queen), 1–3 breeding males, and non-reproductive subordinates of both sexes that are reproductively suppressed while in the colony. To non-invasively evaluate reproductive capacity in the species, we first had to examine the suitability of enzyme immunoassays (EIAs) for determining progestogen and androgen metabolite concentrations in the naked mole-rat, using urine and faeces. A saline control and gonadotrophin-releasing hormone (GnRH) were administered to twelve (six males and six females) naked mole-rats which were previously identified as dispersers and housed singly. The results revealed that urine is possibly not an ideal matrix for progestogen and androgen metabolite quantification in naked mole-rats as no signal was detected in the matrix post GnRH administration. A 5α-Progesterone EIA and an Epiandrosterone EIA were identified as suitable for quantifying faecal progesterone metabolites (fPMs) and faecal androgen metabolites (fAMs) in males and females, respectively. The results suggest that there are individual variations in baseline fPM and fAM concentrations, and only two out of six females and no males exhibited an increase in fPM concentrations greater than 100% (−20% SD) post GnRH administration. Conversely, only four out of six females and three out of six males had an increase in fAM concentrations greater than 100% (−20% SD) following GnRH administration. These results imply that some naked mole-rat individuals have a reduced reproductive capacity even when they are separated from the queen.