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.