The pattern of ovulation in Ansell’s mole-rat, Fukomys anselli : phylogenetic or ecological constraints?

Abstract

The distribution of ovulation patterns and penile ornamentation in mammals is thought to be shaped by sexual selection. Alternatively ovulation pattern have been linked to factors such as phylogeny, social system and ecological constraints but no conclusive pattern has emerged. African mole-rats exhibit a unique range of social organizations and experience diverse ecological condition (i.e. rainfall patterns) with various species exhibiting either induced or spontaneous ovulation in addition to a corresponding variation of penile ornamentation. The members of this family investigated so far do not permit conclusions to be drawn about the importance of phylogenetic versus ecological constraints for the evolution of ovulation pattern since all species of the genus Cryptomys studied occur in mesic habitats and exhibit induced ovulation. In contrast the one representative of the genus Fukomys is a spontaneous ovulator that occurs in arid habitats. The current study aimed to elucidate the factors creating the observed ovulation pattern by using a species within a genus for which so far only spontaneous ovulation has been recorded but unlike the other species with known ovulation mechanisms of this genus it occurs in a mesic environment. Previously non-reproductive Ansell’s mole-rat (Fukomys anselli) females were housed individually for a period of six weeks prior to being housed either alone, in chemical or physical contact with a male. Progesterone profiles generated from urine samples collected throughout the study did not differ significantly either before or after the pairing or between the experimental groups suggesting that they ovulate spontaneously. This was supported by the lack of penile ornamentation found in males of this species. The results suggest that phylogenetic rather than ecological constraints determine the ovulation patterns observed in social bathyergids.