Divergence of reaction norms of size characters between tropical and temperate populations of Drosophila melanogaster and D. simulans

Abstract

Reaction norms to growth temperature of two size‐related traits, wing and thorax length, were compared in tropical (West Indies) and temperate (France) populations of the two sibling species, Drosophila melanogaster and D. simulans. A major body size difference was found in D. melanogaster, with much smaller Caribbean flies, while D. simulans exhibited little size variation between geographical populations. The concave norms of reaction were adjusted to second‐ or third‐degree polynomials, and characteristic points calculated i.e. maximum value (MV) and temperature of maximum value (TMV). TMVs were confirmed to be higher for thorax than for wing length, higher in D. melanogaster than in D. simulans, and higher in females than in males. For both traits Caribbean populations exhibited higher TMVs in the two species, strongly suggesting an adaptive shift of the reaction norms toward higher temperature in warm‐adapted populations. The wing/thorax ratio was also analysed, and found to be significantly lower in tropical populations of both species. This ratio, which is related to wing loading and flight capacity, might evolve independently of body weight itself.

Microspatial structure of Drosophila melanogaster populations in Brazzaville: evidence of natural selection acting on morphometrical traits

“…A more accurate comparison (Scheffé test) showed that Bordeaux had a significantly lower TMV than Loua, and that the value for Kronenbourg was intermediate between these two. This result corroborates previous studies: a higher TMV in a tropical than in a temperate population appears to be an adaptive change to a warmer environment (Morin et al, 1999). The differences in wing length, Figure 2 Reaction norms of wing/thorax ratio in the three populations (1 graph).…”

“…The fact that in Loua the temperature of maximum value of thorax length is higher than it is in Bordeaux suggests that natural selection affects not only trait values, but also their reaction norms. This observation corroborates previous conclusions based on Caribbean populations (Morin et al, 1999).…”

Phenotypic plasticity of elytron length in wingless two-spot ladybird beetles, Adalia bipunctata (Coleoptera: Coccinellidae)

“…The increase in relative wing length as a result of rearing nymphal stages at lower temperatures as we observed has also been found in Drosophila (Stanley, 1935;Noach et al, 1996;Morin et al, 1999) and in mosquitoes (Hosoi, 1954;Van den Heuvel, 1963). It is thought that the switching between morphs in wing dimorphic insects can be influenced by temperature, too.…”

Phenotypic plasticity of body pigmentation in Drosophila melanogaster: Genetic repeatability of quantitative parameters in two successive generations

“…It has been shown (Scheiner, 2002) that, for thorax and wing length, plasticity was genetically variable and could be selected for, although its heritability was much less than that of the traits. Moreover, we know that plasticity may be a target of natural selection and changes when tropical and temperate populations are compared (Delpuech et al, 1995;Morin et al, 1999;Moreteau et al, 2002). The fairly low repeatability of characteristic values of pigmentation reaction norms might be a consequence of an overall low heritability.…”