Morphological variation in a natural population of Drosophila mediopunctata: altitudinal cline, temporal changes and influence of chromosome inversions.

To characterize the morphological variation in a natural population of Drosophila mediopunctata, males were collected on three occasions at a single locality. From each wild-caught male 14 body measures were taken and the karyotype for inversions on chromosomes X and II was determined. Through a principal components analysis, two sources of variation, identified as size and shape, accounted for approximately 80 and 6 per cent of the total morphological variability, respectively. The shape component was determined primarily by variations in the position of the wing second longitudinal vein. Differences between collections were detected both for size and shape. An altitudinal cline was observed in respect of wing shape, although altitude explained only a small part of the shape variation. Size and shape were affected by chromosome II inversions. However, in respect of size, no direct differences were detected between karyotypes but a significant interaction between collecting date and karyotype was found. This suggests that karyotypes might differ in their norms of reaction in the field.