Variation and heritability of aristal morphology in a natural population of Drosophila mediopunctata.

We studied the major sources influencing the variation of the number of aristal branches in a natural population of Drosophila mediopunctata. Flies were collected on six occasions at different altitudes in Parque Nacional do Itatiaia (Brazil). The progenies of these flies were reared in the laboratory at 16.5 degrees C. The number of aristal branches ranges from 11 to 15 and is influenced by sex. Estimates of the natural heritability showed that at least 20% of the total phenotypic variation is due to additive genetic variation. Although the heritability of this trait estimate in the laboratory was larger (42%), the difference between the two estimates is not statistically significant. Thus, for the number of aristal branches, laboratory estimates of heritability provide reasonable estimations of both the magnitude and significance of heritabilities in nature. The mean numbers of aristal branches in the wild-caught flies from different altitudes or months are homogeneous. The same was observed for the means of its progeny kept in the laboratory under controlled conditions. On the other hand, wild-caught females have significantly fewer aristal branches than their laboratory-raised daughters, which suggests that an environmental factor or factors may have an important influence on this trait.