Interspecific hybridization was used to determine the genetic relationships between the four species of mosquitoes in the Triseriatus and Zoosophus groups of the aedine subgenus Protomacleaya (Diptera : Culicidae) . Four factors were investigated : 1) fertility of intra- and interspecific crosses, 2) morphology of the interspecific hybrids and the genetic bases of morphological characters, 3) modes of postcopulatory reproductive isolation and 4) types of chromosomal changes occurring during and subsequent to the divergence of the species .
Hybrid progeny were produced in 11 of the 12 possible crosses between the four species . Only the Aedes zoosophus female X A . brelandi male cross failed to produce adult progeny . One additional cross, A . hendersoni females X A . brelandi males, had greatly reduced fertility . Fewer than 1% of the eggs in this cross were embryonated .
Crosses between the morphologically distinct species, A . triseriatus and A. zoosophus, revealed that each of the three most conspicuous morphological differences was controlled by a single gene. These loci were placed on a previously published linkage map for the species. Copper thorax ( co) was on linkage group II . Abdominal banding (Ab) and banded tarsi (Bt) were both on linkage group III .
Two types of postcopulatory reproductive isolation were present . A . brelandi and A . hendersoni were separated by unidirectional sterility possibly of cytoplasmic origin . All of the other species combinations were separated by the production of sterile intersex progeny in some or all of the crosses . The genetic basis of intersex was polyfactorial.
Meiotic abnormalities were observed in all of the interspecific hybrids except for those of A . brelandi and A. hendersoni. Reduced chiasmata frequency was the most common abnormality. Other meiotic abnormalities observed were dicentric bridges with acentric fragments and chromosomal breakage. At least one fixed inversion separated A. zoosophus from the other species.
The status of A . brelandi as a species distinct from A. hendersoni was confirmed by the presence of unidirectional incompatibility. Genetically, the morphologically distinct species A. zoosophus was found to be almost as similar to A. triseriatus as was A . triseriatus to its sibling species A . hendersoni. Though post-copulatory mechanisms reducing gene flow were present between each of the species, gene flow was possible between all four species .
- sex determination,
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