Founder effect in an island population of bighorn sheep

The Tiburon Island population of desert bighorn sheep has increased in size from 20 founders in 1975 to approximately 650 in 1999. This population is now the only population being used as the source stack for transplantations throughout northern Mexico. To evaluate the genetic variation in this popu lation we examined 10 microsatellite loci and a major histocompatibility co mplex (MHC) locus. The genetic variation was significantly less than found in other populations of the same subspecies in Arizona. Using a model that takes into account the effects of genetic drift on genetic distance, most o f the genetic distance observed between the Tiburon population and Arizona samples could be explained. Because of the low genetic variation found in t he Tiburon population, it is suggested that the Tiburon population should b e supplemented with additional unrelated animals or that the transplant pop ulations should be supplemented with unrelated animals.