Abstract
The color pattern was observed on abdominal tergites of Drosophila nigromaculata obtained from thirteen localities in Hokkaido as shown in Table 1. Six different spot-patterns were distinguished in 9391 specimens and referred to as SA-, SB-, SC-, SD-, SE- and SF-types (Fig. 1). It was found that the frequency of each type varied according to different localities and seasons, and that, in natural populations, SD- and SA-types appear in the highest frequency, followed by SE- and SC-types, and SB- and SF-types were rare in occurrence.
Monthly fluctuation of each type was observed in samples from the University Botanical Garden in 1961 and 1962. It suggests that D. nigromaculata exhibits a balanced polymorphism in the spot-patterns.
Some preliminary cross-experiments were carried out on the spot-patterns of SA-, SD-, SE- and SF-types. Two strains, SA and SD were established through seven or eight generations. Crosstests were carried out between them. The SE-type was dominant over the SA-type, in both F1 females and males. At the present situation an interpretation is not impossible that these spot-patterns are controlled by a single pair of alleles, and that their expression is affected by the environmental factors.
