Abstract:
Cooperative behaviour, sociality and reproductive suppression in African mole-rats have been extensively studied. Nevertheless, endocrine correlates of some species of social mole-rats have been neglected, and these species may hold the key to understanding the behavioural and physiological complexity that allows the maintenance of social groups in African mole-rats. In this study, we investigated endocrine correlates implicated in the suppression of reproduction and cooperative behaviours, namely glucocorticoids (a stress-related indicator) through faecal glucocorticoid metabolites (fGCMs), plasma testosterone (an indicator of aggression) and plasma prolactin in the Mahali mole-rat (Cryptomys hottentotus mahali) across reproductive classes (breeding females and males, non-breeding females and males) and season (wet and dry). Breeders possessed higher levels of testosterone than non-breeders. In reproductively suppressed non-breeding females, fGCMs were significantly higher than in breeders. Furthermore, an adrenocorticotropic hormone stimulation test (ACTH challenge test) on both male and female non-breeders revealed that female non-breeders show a more significant response to the ACTH challenge than males. At the same time, plasma prolactin levels were equally elevated to similar levels in breeding and non-breeding females. Chronically high levels of prolactin and fGCM are reported to cause reproductive suppression and promote cooperative behaviours in non-breeding animals. Furthermore, there was a negative relationship between plasma prolactin and progesterone in non-breeding females. However, during the wet season, a relaxation of suppression occurs through reduced prolactin which corresponds with elevated levels of plasma progesterone in non-breeding females. Therefore, prolactin is hypothesised to be the primary hormone controlling reproductive suppression and cooperative behaviours in non-breeding females. This study provides new endocrine findings for the maintenance of social suppression in the genus Cryptomys.
Description:
The following are the supplementary data related to this article. SUPPLEMENTARY FIGURE Fig. 1. Assay validation revealed by parallelism of serial dilutions of spiked plasma pools for Mahali mole-rats, with standard for the prolactin ELISA assay. Relative variation (%) of the slope of respective trendlines were <2% for Mahali mole-rats plasma. OD is the optical density measures the ELISA colour change, which is proportional to the concentration of prolactin.
SUPPLEMENTARY TABLES. TABLE S1. Comparison of general linear models tested to explain body mass (g) as a function of season and reproductive status in Mahali mole-rats (Cryptomys hottentotus mahali). Best model fits are ranked by AICc, while model weights are estimates across all models and add up to 1.
TABLE S2. Comparison of general linear models tested to explain variation in faecal glucocorticoid metabolite (fGCM, μg/g) concentrations as a function of season and reproductive status in Mahali mole-rats (C. h. mahali). Best model fits are ranked by AICc, while model weights are estimates across all models and add up to 1.
TABLE S3. Comparison of generalised linear models tested to explain plasma testosterone concentrations (ng/dl) as a function of season and reproductive status in Mahali mole-rats (C. h. mahali). Best model fits are ranked by AICc, while model weights are estimates across all models and add up to 1.
TABLE S4 Comparison of general linear models tested to explain plasma progesterone concentrations (ng/ml) as a function of season and reproductive status in Mahali mole-rat (C. h. mahali) females. Best model fits are ranked by AICc, while model weights are estimates across all models and add up to 1.
TABLE S5. Comparison of general linear models tested to explain plasma prolactin concentrations (ng/ml) as a function of season and reproductive status in Mahali mole-rat (C. h. mahali) females. Best model fits are ranked by AICc, while model weights are estimates across all models and add up to 1.