Microsatellite evolution in congeneric mammals: domestic and bighorn sheep

We compared genotypes at eight (AC)n microsatellite loci in domestic sheep(Ovis aries) and wild Rocky Mountain bighorn sheep (O. canadensis). Thedomestic sheep had greater genetic variation, higher allele-size variances,and larger allele sizes than the wild sheep. Accumulating evidence fromhigher taxonomic comparisons shows that these parameters are biased ifmicrosatellite loci are selected in one taxon and used in another. Ourresults demonstrate similar biases between congeneric species. We comparedstandard measures of genetic variation, differentiation, and distancewithin and between species (H, D, FST) to newer measures based onallele-size variance (SW, SB, RST). The size-based distances betterdetected species-level divergence, but standard measures betterdistinguished allopatric populations. Empirical calibration of thesemeasures at the subspecies level is needed to establish their usefulranges.