Patterns of Allozyme Relationships Compared with Morphology, Hybridization, and Geologic History in Allopatric Island-Dwelling Mosquitoes

Abstract

Allozyme relationships were compared with morphology, interspecific hybridization, and geologic history in 14 closely-related species in the Aedes (Stegomyia) scutellaris subgroup. The phylogeny generated by the electrophoretic data was generally in agreement with morphological classifications except that one morphologically distinct species pair (A. alcasidi and A. malayensis) showed only populational differentiation and several nearly identical morphological pairs in Polynesia (e.g., A. pseudoscutellaris and A. polynesiensis) were very distant genetically. A molecular clock, based on the ratio between genetic distance and divergence time (one unit of Nei's distance = 11 million years) inferred from a dated geologic event, was used to compare zoogeography, morphology, and biochemical relationships. Genetic distances between species from the Solomon Islands and the Vanuatu-Polynesia area correspond to an early Pliocene separation of these areas. An invasion of Micronesia occurred approximately 5 million years ago. Most remaining speciation occurred during the mid-Pliocene as islands moved into their present-day positions. The close relationship between southeast Asian and Philippine species could have resulted from the recent onset of isolation in the Pleistocene. Interspecific hybridization potential was not significantly correlated with Nei's genetic distance. Many quite distantly related species readily hybridize, while some closely related pairs show only unidirectional compatibility. Slight interspecific morphological divergence and the independence of hybridization capabilities from phylogeny are not unexpected in a group in which species are allopatric and occupy similar habitats.

Intraspecific and interspecific variation in the sequence and abundance of highly repeated DNA among mosquitoes of the Aedes albopictus subgroup

“…These include two strains of A. albopictus (from Borneo and Malaysia), two other albopictus subgroup species, A. pseudalbopictus and A. seatoi (from Malaysia and Thailand, respectively), and two scutellaris subgroup species, A. malayensis and A. hebrideus (from Malaysia and Melanesia, respectively). The abundance profiles of species in this cluster appear stable since species in the two subgroups have probably been isolated for 10-15 million years (Pashley et al, 1985). It is unlikely that there has been horizontal transfer (introgression) of sequences since there is complete post-mating and complete or significant pre-mating isolation between species (McLain et a!., 1985;.…”

“…Since highly repeated sequences evolve rapidly through single base substitution (Pages and Roizes, 1984), a given family may be represented by different sequence variants scutellaris subgroups diverged approximately 10 million years ago (Pashley et a!., 1985;Pashley and Rai, 1983). However, it is unlikely that there is much sequence variation within a family within a given population since the rate of homogenisation of a variant is high relative to the mutation rate (Strachan et a!., 1985).…”

“…!aris 7-10 million year ago (Pashley et aL, 1985). A. hebrideus and A. pseudoscute!laris appear to have diverged about 5 million years ago (Pashley et a!., 1985).…”

“…!aris 7-10 million year ago (Pashley et aL, 1985). A. hebrideus and A. pseudoscute!laris appear to have diverged about 5 million years ago (Pashley et a!., 1985). Phylogenetic relationships within the A. a!bopictus subgroup have yet to be elucidated, although A. pseuda!bopictus and A. seatoi are probably more closely related to each other than to A. albopictus while A. flavopictus is probably relatively distantly related to the other three species (Rai et a!., 1982).…”

Morphological Stasis abd Molecular Divergence in the Intercontinental Disjunct Genus Datisca (Datiscaceae)

“…Molecular data have been successfully applied to biogeographical questions in animals such as the Old and New World monkeys (Sarich and Cronin 1980), Pacific island-dwelling mosquitoes (Pashley, Rai, and Pashley 1985), and within the Drosophila melanogaster species complex (Lachaise, Cariou, David, Lemeunier, Tsacas, and Ash burner 1988). In plants, isozyme electrophoresis has been used extensively to quantify genetic variation; but only limited use has been made of these data in examining intercontinental disjunctions (V ogelmann and Gastony 1987;Parks and Shan-An 1988;Hoey and Parks 1988;Liston, Rieseberg, and Elias 1989).…”