The pattern of ovulation in Ansell's mole-rat: phylogenetic or ecological constraints?

The distribution of ovulation patterns and penile ornamentation in mammals is thought to be shaped by sexual selection. Alternatively, ovulation patterns 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 conditions (i.e. rainfall patterns), with various species exhibiting either induced or spontaneous ovulation in addition to a corresponding variation of penile ornamentation. Investigations of members of this family conducted so far do not allow conclusions to be drawn about the importance of phylogenetic versus ecological constraints for the evolution of ovulation patterns because 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 6 weeks before 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.