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.
