Abstract:
INTRODUCTION: The Damaraland mole-rat (Fukomys damarensis) is a eusocial, subterranean mammal, which
exhibits an extreme reproductive skew with a single female (queen) monopolizing reproduction in each colony.
Non-reproductive females in the presence of the queen are physiologically suppressed to the extent that they
are anovulatory. This blockade is thought to be caused by a disruption in the normal gonadotropin-releasing
hormone (GnRH) secretion from the hypothalamus. In order to understand the underlying physiological mechanisms
of reproductive suppression in subordinate females we studied the expression of steroid hormone receptors and the
androgen-converting enzyme aromatase in forebrain regions involved in the control of reproductive behaviour in
female breeders and non-breeders from intact colonies. Additionally, we included in our analysis females that
experienced the release from social suppression by being removed from the presence of the queen.
RESULTS: We found expression of androgen receptor, estrogen receptor α and aromatase in several forebrain
regions of female Damaraland mole-rats. Their distribution matches previous findings in other mammals. Quantification
of the hybridisation signal revealed that queens had increased expression of androgen receptors compared to
non-breeders and removed non-breeders in most brain regions examined, which include the medial preoptic
area (MPOA), the principal nucleus of the bed nucleus of the stria terminalis (BSTp), the ventromedial nucleus of
the hypothalamus (VMH), the arcuate nucleus (ARC) and the medial amygdala (MeA). Furthermore, breeders had
increased estrogen receptor α expression in the anteroventral periventricular nucleus (AVPV) and in the MeA,
while aromatase expression in the AVPV was significantly reduced compared to non-breeders. Absence of social
suppression was associated with increased androgen receptor expression in the ARC, increased estrogen receptor
α expression in the MeA and BSTp and reduced aromatase expression in the AVPV.
CONCLUSION: This study shows that social suppression and breeding differentially affect the neuroendocrine
phenotype of female Damaraland mole-rats. The differential expression pattern of estrogen receptor α and aromatase
in the AVPV between breeders and non-breeders supports the view that this region plays an important role in
mediating the physiological suppression in subordinate females.
