Breeding status affects the expression of androgen and progesterone receptor mRNA in the brain of male Damaraland mole-rats

Abstract

The eusocial Damaraland mole-rat (Fukomys damarensis) represents an extreme example of reproductive skew, in that reproduction is completely blocked in female subordinate group members. Similarly, male subordinates within the colony show no sexual behaviour. In contrast to females, however, non-reproductive males have functional gonads and do not differ in circulating levels of pituitary hormones and testosterone from reproductive males. Nevertheless, they have reduced numbers of follicle-stimulating hormone receptors in their testes and they produce fewer spermatozoa with a large proportion of immature spermatozoa and precursors. To understand the mechanism of reproductive suppression operational in subordinate males we studied the expression of androgen and progesterone receptor genes in forebrain regions involved in the control of reproductive behaviour in male breeders and nonbreeders from intact colonies. While it is well documented that testosterone activates maletypical behaviour, the role of progesterone in this process is less clear as previous studies have produced contradictory results. We found expression of androgen receptor (AR) and progesterone receptor (PGR) genes in several forebrain regions of male Damaraland molerats. The distribution of AR in males matches our previous findings in females. This is the first report showing the distribution of PGR in mole-rats. We found PGR in all areas which were also sensitive to androgens and estrogens. Analysis of the optical densities of the AR and PGR hybridisation signal revealed that breeding males had increased expression of AR and PGR compared to non-breeders in most brain regions examined, which include the medial preoptic area, the bed nucleus of the stria terminalis, the ventromedial nucleus of the hypothalamus, the arcuate nucleus and the medial amygdala. These status-related differences were more pronounced for PGR than for AR. This study shows that breeding position affects the neuroendocrine phenotype of male Damaraland mole-rats. Further, it suggests that androgens and progesterone might act synergistically in activating sexual behaviour in males.