Colonization of America by Drosophila subobscura: spatial and temporal lethal-gene allelism

About twenty years ago Drosophila subobscura, a western Palearctic species, colonized both North and South America. Lethal genes in the O chromosome h as been subject to much research. Lethal gene allelisms between American po pulations far away have been studied. These allelisms were not negligible, but all cases were due to the lethal gene completely associated to the O-5 chromosomal inversion. Here we analyze the lethal genes in a new American p opulation of D. subobscura (Centralia. Washington), located fairly close to a previously studied population (Bellingham. Washington) and separated in space and time with other American populations (Gilroy I and II in Californ ia and Santiago de Chile). The frequencies of lethal and semilethal gents o f Centralia were 16.9 +/- 4.6 and 6.2 +/- 3.0. respectively. The intrapopul ational allelism of Centralia was 0.122 +/- 0.036. Interpopulational alleli sms were studied using the lethal genes from the populations separated in s pace and rime from Centralia. The interpopulational allelisms between Centr alia and Gilroy I(California) and between Centralia and Bellingham (Washing ton) were higher than the intrapopulational allelism (0.155 +/- 0.032 and 0 .153 +/- 0.024, respectively). In all these cases allelism was due to a com plete association between a lethal gene and the O-5 chromosomal inversion. Accordingly, no other lethal genes are shared in these populations.