Quantitative trait analysis and geographic variability of natural populations of Zaprionus indianus, a recent invader in Brazil.

Five natural samples of a recent South America invader, the drosophilid Zaprionus indianus, were investigated with the isofemale line technique. These samples were compared to five African mainland populations, investigated with the same method. The results were also compared to data obtained on mass cultures of other populations from Africa and India. Three quantitative traits were measured on both sexes, wing and thorax length and sternopleural bristle number. We did not find any latitudinal trend among the American samples, while a significant increase in body size with latitude was observed in the Indian and, to a lesser degree, in the African populations. American populations were also characterized by their bigger size. Genetic variability, estimated by the intraclass correlation among isofemale lines, was similar in American and African populations. The intraline, nongenetic variability was significantly less in the American samples, suggesting a better developmental stability, the origin of which is unclear. A positive relationship was evident between intraline variability of size traits and the wing-thorax length correlation. Altogether, our data suggest that the colonizing propagule introduced to Brazil had a fairly large size, preventing any bottleneck effect being detected. The big body size of American flies suggests that they came from a high-latitude African country. The lack of a latitudinal dine in America seems to be related to the short time elapsed since introduction. The very rapid spread of Z. indianus all over South America suggests that it might rapidly invade North America.