Comparison of Population Structure in Chromosomally Polytypic and Monotypic Species of Sceloporus (Sauria: Iguanidae) in relation to Chromosomally-Mediated Speciation
Thompson, P.; Sites, J.W.
Evolution; International Journal of Organic Evolution 40(2): 303-314
Sceloporus grammicus has been used as an example of stasipatric speciation, and some models of chromosomal speciation have assumed that the fission rearrangements which distinguish the chromosome races within this complex are negatively heterotic in the heterozygous state. Consequently, such rearrangements are assumed to be fixed by drift in small, inbred populations. Allelic variation at 19 presumptive gene loci was examined in 13 samples of a chromosomally conservative congener, Sceloporus graciosus, and was compared to an equivalent data set for the chromosomally polytypic S. grammicus. Several estimates of population variability and structure were calculated, and results were inconsistent with models of extreme population subdivision and/or frequent bottlenecks and extinction-colonization events in S. grammicus. For example, mean level of heterozygosity and mean number of alleles per locus were significantly higher in S. grammicus than in S. graciosus, while the average genetic distance (D) was significantly higher in S. graciosus. These results are considered in light of expected "Wrightian" population genetic parameters, and we conclude that S. grammicus does not seem to have the population structure necessary for the fixation of strongly negatively heterotic rearrangements.