An adaptive chromosomal polymorphism affecting size-related traits, and longevity selection in a natural population ofDrosophila buzzatii

Abstract

Size-related phenotypic variation among second-chromosome karyotypes in Drosophila buzzatii was examined in an Argentinian natural population. For all measured traits (thorax and wing length; wing, head and face width), this inversion polymorphism exhibited a significant and (additive) 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 removed with Burnaby's method. Likewise, in an experiment of longevity selection in the wild, variation in chromosomal frequencies was verified 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 selection is consistent with a pattern of antagonistic selection detected in previous studies on the inversion polymorphism.

Correlations among size-related traits are affected by chromosome inversions in an adaptive polymorphism in Drosophila buzzatii

“…Because any effects of age were experimentally removed, these results do not confound direct karyotypic effects with indirect effects caused by differential longevity related to body size (see Ruiz et a!., 1991;Norry et a!., 1995b).…”

“…This finding does not imply that R is independent of environmental deviations, but supports the hypothesis that homokaryotypic variation in CP-R is not only an environmental variation, but partially genetic. Nonadditive effects of the second chromosome inversions, on the other hand, would be apparently very weak on sizerelated traits in D. buzzatii, as most of the phenotypic variance among karyotypes is explained by a linear regression of trait on chromosome dose (Ruiz et a!., 1991;Hasson et a!., 1992;Norry et a!., 1995b).…”

“…19), it is of interest to detect factors affecting genetic correlations among traits phenotypically correlated with fitness components. Chromosomal inversions could be one of such factors in D. buzzatii, because the second chromosome inversions affect body size and morphometric traits correlated with it (Ruiz et a!., 1991;Hasson et al, 1992;Norry et aL, 1995b). This hypothesis is examined in the present study.…”

“…This population is polymorphic for four inversions on the second chromosome, namely standard (st), j, jz3 and jq7 . Detailed information on the data gathering methods can been found in Norry et al (1995b), and a brief description follows.…”

The evolutionary history of Drosophila buzzatii. XXXIII. Are Opuntia hosts a selective factor for the inversion polymorphism?

“…Research work in D. buzzatii has shown a significant relationship between the inversion polymorphism and body size Hasson et at., 1992a) and other morphometric traits (Norry et at., 1995). The analysis of these traits in original and colonized populations may provide the genetic framework to test the hypothesis of a genetic reorganization after the founder event.…”