Variation in ovarian morphology in four species of New World moles with a peniform clitoris

Abstract

Female moles of the Old World genus Talpa display a curious suite of reproductive features that include a peniform clitoris and ovaries with a discrete interstitial gland or testis-like region (so-called 'ovotestes'). The masculinization of the female external genitalia in Talpa has accordingly been linked with secretion of androgens from the interstitial gland region of the fetal gonad. Although their ovarian morphology has received less attention, some species of New World moles also have ovaries with a pronounced interstitial gland (for example star-nosed mole, Condylura cristata), whereas females of other species do not (for example eastern mole, Scalopus aquaticus). Although it is difficult to determine the sex of both Old and New World moles, published accounts describing the external genitalia of female moles are available only for Talpa. The hypothesis that masculinization of the female external genitalia in moles is associated with the presence of an ovarian interstitial gland (OIG) was tested in the present study by using a comparative approach to determine whether these features are ever found in isolation of one another. Three genera of North American moles (Scapanus, Condylura and Neurotrichus) were studied and a peniform clitoris was found in all three species, but OIG were found in only two of three genera. The ovaries of S. latimanus and S. orarius were unremarkable, with no evidence of a discrete interstitial gland or testis-like region. Mapping these results onto recent talpid phylogenies indicates that loss of the bipolar ovarian morphology is a derived trait in Scapanus, and conclusively demonstrates that masculinization of the external genitalia in female moles can develop in the presence or absence of 'ovotestes'.