Reaction norms of size characters in relation to growth temperature in Drosophila melanogaster: an isofemale lines analysis

• Published in: Genetics selection evolution (Paris) 1994-06, Vol.26 (3), p.229-251, Article 229
• Main Authors: DAVID, J. R, MORETEAU, B, GAUTHIER, J. P, PETAVAY, G, STOCKEL, A, IMASHEVA, A. G
• Format: Article
• Language: English
• Subjects: Analysis; Animal genetics; Animals; Biological and medical sciences; Classical genetics, quantitative genetics, hybrids; Drosophila; Drosophila melanogaster; Fundamental and applied biological sciences. Psychology; Genetics; Genetics of eukaryotes. Biological and molecular evolution; Growth; Invertebrata; Life Sciences
• ISSN: 0999-193X; 1297-9686; 1297-9686
• DOI: 10.1186/1297-9686-26-3-229

Ten isofemale lines of Drosophila melanogaster, recently collected in a French vineyard, were submitted to 7 different developmental temperatures, from 12 to 31 degree C, encompassing the whole physiological range of the species. For each line and temperature, 10 flies of each sex were collected randomly and 2 size-related traits were measured: wing and thorax length. Both traits exhibited similar response curves: a maximum size at a low temperature and a decrease on both sides. ANOVA showed significant variations between lines and also significant line-temperature interactions, demonstrating different norms of reaction among the various lines. The shapes of the curves were further analysed by considering slope variations, ie by calculating empirical derivative curves. The most interesting observation is that the temperature of maximum size (TMS) is not the same for the wing (average 15.73 plus or minus 0.29 degree C) and the thorax (average 19.57 plus or minus 0.47 degree C). Genetic differences seem to exist between lines, and TMS for both traits are correlated. Sexual dimorphism was analysed by considering the female/male ratio for wing and thorax. Both traits provided the same information: sexual dimorphism increased, from 1.10 to 1.16, with increasing temperature, and significant differences were found between lines. Finally, the wing/thorax ratio appeared as an original and most interesting trait. This ratio, which is less variable than wing or thorax, exhibited a monotonously decreasing sigmoid shape, from 2.80 to 2.40, with increasing temperature. It is suggested that this ratio, which may be related to flight capacity at various temperatures, could be the direct target of natural selection.