Social structure predicts genital morphology in African mole-rats.
BACKGROUND
African mole-rats (Bathyergidae, Rodentia) exhibit a wide range of social structures, from solitary to eusocial. We previously found a lack of sex differences in the external genitalia and morphology of the perineal muscles associated with the phallus in the eusocial naked mole-rat. This was quite surprising, as the external genitalia and perineal muscles are sexually dimorphic in all other mammals examined. We hypothesized that the lack of sex differences in naked mole-rats might be related to their unusual social structure.


RESULTS
We compared the genitalia and perineal muscles in three African mole-rat species: the naked mole-rat, the solitary silvery mole-rat, and the Damaraland mole-rat, a species considered to be eusocial, but with less reproductive skew than naked mole-rats. Our findings support a relationship between social structure, mating system, and sexual differentiation. Naked mole-rats lack sex differences in genitalia and perineal morphology, silvery mole-rats exhibit sex differences, and Damaraland mole-rats are intermediate.


CONCLUSIONS
The lack of sex differences in naked mole-rats is not an attribute of all African mole-rats, but appears to have evolved in relation to their unusual social structure and reproductive biology.
Seney
Marianne L
ML
Center for Neuroendocrine Studies and Department of Psychology, University of Massachusetts, Amherst, MA, USA. marianne.seney@gmail.com
Kelly
Diane A
DA
Goldman
Bruce D
BD
Sumbera
Radim
R
Forger
Nancy G
NG
D000818:Animals; D001522:Behavior, Animal; D005260:Female; D008297:Male; D019577:Mole Rats / Q000033:anatomy & histology* / Q000502:physiology*; D009132:Muscles / Q000473:pathology; D010413:Penis / Q000033:anatomy & histology / Q000502:physiology; D010502:Perineum / Q000033:anatomy & histology / Q000502:physiology; D010802:Phylogeny; D012727:Sex Characteristics; D012726:Sexual Behavior, Animal; D012919:Social Behavior; D013045:Species Specificity; D013997:Time Factors