Genetic distance between two sibling species of the Aedes mariae complex (Diptera, Culicidae)

Two sibling species of the mariae complex of the Aedes genus have been studied: Ae. mariae and Ae. zammitii. Thee mosquitoes are allopatric and show similar adaptations to rocky mediterranean coasts. The isolating mechanisms between the two species are well studied. A partial sterility of hybrid F1, limited to males, has been found with laboratory cross experiments. Strong pre-mating isolating mechanisms were shown in nature by means of release experiments, the frequency of hybrids never exceeding 2% without evidence of introgression. We analyzed genetic variation at 26 enzyme loci in a population of each species: 35% of loci were polymorphic, with an observed mean heterozygosity of 0.07 in Ae. mariae and 0.06 in Ae. zammitii; 6 loci allow discrimination between the two species at a probability of at least .99. Nei's measures of genetic identity and genetic distance are respectively I = 0.6096 and D = 0.2828. The distribution of genetic identities relative to loci is strongly bimodal, reflecting a different contribution of highly variable and fast evolving loci on one side and conservative and slowly evolving loci on the other. We consider, on the base of various experimental data (see Powell, 1975), in the first class ("fast evolving" loci) both variable substrate and regulatory enzymes, in the second ("slow evolving" loci) non regulatory enzymes. Values of genetic distance calculated separately for the "fast" (54% of the loci studied) and "slow" (46%) evolving loci are respectively Df = 0.41 and Ds = 0.03, showing that the main contribution to genetic distance in the first period of divergence is due to fast evolving loci, whose rate of evolution is about ten times more rapid with respect to slow evolving loci.