Evolutionary genetics of Zaprionus. II. Mitochondrial DNA and chromosomal variation of the invasive drosophilid Zaprionus indianus in Egypt.

Zaprionus indianus is an Afrotropical drosophilid species that has expanded its geographical range in the Palearctic region and the Americas during the second half of the last century. It has invaded Egypt within the past two decades from East Africa or Asia and became a dominant species in the drosophilid fauna therein, but the exact date of introduction and source of the propagule remain unknown. Here, we investigate the genetic structure of eight geographical populations within and around the Nile Delta using mitochondrial DNA sequences of the cox2 gene and chromosomal inversion polymorphism. A very low level of genetic variability was detected for both markers, mainly attributed to the introduction bottleneck. Nonetheless, both indicate a significant population structure, with a southeastern-northwestern cline. Demographic history analysis suggested northwestern populations to be younger (expanding in ca. 1992) than southeastern ones (expanding in ca. 1985). The In(II)A polymorphism was only observed in the northwestern population, but one-year interval analysis of the Alexandria population revealed the lack of seasonal fluctuation and a trend toward the loss of the polymorphism. Based on these data and faunistic records, we propose a multiple introduction scenario for Z. indianus in Egypt-according to which a first wave in the early 1980s from Sudan through normal northward range expansion or fruit trade, and a second wave in the early 1990s from Asia via fruit trade. We also suggest, from ecological observations, fruit trade data and known adaptive versatility of Z. indianus, date palm, the dominant fruit in Egypt and in the oases where Z. indianus predominates, to play a major role in the spread of the species in the Middle East.