Reproductive isolation in three populations of the striped mouse Rhabdomyspumilio (Rodentia, Muridae): interpopulation breeding studies

Reproductive isolation was studied in three populations of the striped mous e Rhabdomys pumilio. Two populations, Alice and Goegap, had the same diploi d number of 48, while the other population, Irene, had a diploid number of 46. The populations represent three extremes of the distributional range of the species in South Africa. Interpopulation breeding and postnatal growth of hybrids were studied to test for post-zygotic reproductive isolation am ong the populations. Breeding success was high (> 73 %) in intrapopulation pairs and extremely reduced in interpopulation pairs, which showed also hig h levels of aggression. Of the interpopulation pairs, male Goegap x female Alice crosses had the best reproductive success (i.e. 53 %), but litter siz e was significantly lower than that of intrapopulation pairs, and the hybri ds had retarded pre-weaning growth and low reproductive success. Alice x Ir ene and Goegap x Irene pairs had little or no success, and their hybrid you ng had respectively no reproductive success or high pre-weaning mortality. Although there are indications of hybrid failure, the inability of interpop ulation pairs to produce many offspring did not permit thorough testing of hybrid fitness and viability. Instead, the data obtained suggest that pre-m ating instead of post-zygotic barriers prevent interfertility of the three populations.