Restric1ion patterns of mitochondrial DNA, esterase isozyme electromorphs, and chromosome inversions were chosen as indicators to investigate the genetic variability of natural populations of a sibling species pair, Drosophila immigrans and D. formosana, in Taiwan. In addition to local populations, we also surveyed sixteen laboratory-maintained stocks of the cosmopolitan species D. immigrans originating from different countries. All three indicators consistently showed that the local populations of both species in Taiwan have a very low genetic variation. No trace of introgression was found although they can produce fertile hybrids. The low genetic variability of these two species may be due to both the founder effect and their recent establishment in Taiwan.
Chromosome inversions, Esterase isozymes, Founder effect, Genetic variation, MtDNA restriction patterns
