NEW DISCRIMINATING TRAITS BETWEEN FEMALES OF 2 SIBLING SPECIES - DROSOPHILA-MELANOGASTER AND DROSOPHILA-SIMULANS (DIPTERA, DROSOPHILIDAE)

Females of the two sibling cosmopolitan species D. melanogaster and D. simulans are generally considered as very similar and impossible to distinguish, especially under field conditions. Various traits have been proposed to separate the species but the only completely diagnostic character is the length of egg filaments. This requires, however, either isolating each female in a culture vial, or dissecting its ovaries. We have found two new traits which provide complete discrimination between laboratory grown flies, i.e. the pattern of abdominal pigmentation and the wing/thorax ratio. These two traits can also be used for sorting out the two types of females in wild living samples. However the discrimination, which is efficient, does not provide absolute certainty, because of a much greater phenotypic variability. Interspecific hybrids are intermediate between parents and cannot be readily identified with these characters. For wing and thorax lengths and ratio, a dominance of D. simulans was observed in hybrids, as well as an important increase of individual variability.