Lack of seasonal changes in mitochondrial DNA variability of a Drosophila subobscura population

Restriction site analysis of mtDNA of 550 isofemale lines corresponding to different seasonal samples of a single geographic population of Drosophila subobscura was carried out. The distribution pattern of haplotypes was similar to that observed for the entire range of the species on the European continent: two haplotypes were equally and highly frequent, and a set of sporadic haplotypes were almost never present in more than one seasonal sampling. No statistically significant evidence was found for between-population heterogeneity across time, and the mean within-population variation was similar to other mtDNA restriction site analyses previously reported for D. subobscura populations. These observations could be interpreted in terms of the neutral mutation hypothesis where the entire population has not yet reached an equilibrium. The causes of this non-equilibrium are most likely periodic winter bottlenecks, phenomena that particularly affect the distribution of mtDNA haplotypes across time.