Extensive protein and microsatellite variability in an isolated, cyclic ungulate population.

We investigated polymorphism at protein and microsatellite DNA loci in an isolated, unmanaged and cyclic population of Soay sheep on the island of Hirta, St. Kilda. Extensive molecular variation was revealed at both protein loci (mean heterozygosity 7.78 per cent) and microsatellite loci (mean heterozygosity 50.93 per cent). Typically, large mammals possess limited protein variation and we were surprised to observe such a level of protein heterozygosity, particularly considering the genetic history of the Hirta population. Indeed, compared to other mammals, Soay sheep lie within the top 17 per cent of the distribution of average protein heterozygosities. We discuss the level of protein heterozygosity in the context of other mammalian species, other breeds of sheep and the genetic history of Soay sheep. Possible explanations for a large average and interlocus variance in protein heterozygosity are proposed. Although little data are available from other studies to compare with microsatellite DNA variability in this population, we discuss the potential application of microsatellite markers to interpopulation and interspecific genetic studies.