AN ADAPTIVE CHROMOSOMAL-POLYMORPHISM AFFECTING SIZE-RELATED TRAITS, AND LONGEVITY SELECTION IN A NATURAL-POPULATION OF DROSOPHILA-BUZZATII

Size-related phenotypic variation among second-chromosome karyotypes i n Drosophila buzzatii was examined in an Argentinian natural populatio n. For all measured traits (thorax and wing length; wing, head and fac e width), this inversion polymorphism exhibited a significant and (add itive) linear contribution to the phenotypic variance in newly emerged wild flies. The results suggest that only overall body size, and not body shape, is affected. as no karyotypic variation was found for any trait when the effects of differences in within-karyotype size were re moved with Burnaby's method. Likewise, in an experiment of longevity s election in the wild, variation in chromosomal frequencies was verifie d in the direction predicted on the basis of: (i) previous studies on longevity selection for body size in the wild and (ii) the pattern of chromosomal effects we observed on size. The direction of such selecti on is consistent with a pattern of antagonistic selection detected in previous studies on the inversion polymorphism.