Allozyme and chromosomal polymorphism ofDrosophila buzzatii in Brazil and Argentina

Allozyme polymorphism in the colonizing populations ofD. buzzatii in Australia is quite low (average heterozygosity of 0.051 ± 0.025), but no comparative data are available for the species in other introduced populations or in its presumed area of origin, the Chaco of Argentina. For 12 localities in Argentina and five in Brazil, average expected heterozygosity is not significantly different from that in Australia. However, there appears to have been a loss of genetic variability on introduction of the species to Australia, as five loci are variable in South America that are monomorphic in Australia, and one additional allele was detected at each of six other loci in South America. Our results for inversion polymorphism in Argentina are consistent with previous data, but some Brazilian populations apparently have reduced inversion polymorphism. With the exception of those nearest the Chaco, these Brazilian populations may have resulted from passive colonization within historical times due to transport by man, and could represent both primary and secondary colonizations. However, the allozyme data do not readily fit a colonization hypothesis, and theD. buzzatii populations of both northeast and southeast Brazil may be relic populations. More detailed study of inversion and allozyme polymorphism in Brazil is necessary to provide critical data on the evolutionary history of this species.