Investigation on early divergence between populations of Drosophila melanogaster kept at different temperatures
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phenotypic differentiation between the two populations is already detectable in earlier generations of selection;
the divergence is more related to a changed body shape than to body size;
this divergence is correlated with fitness and, therefore, natural selection may operate on these differences.
progress in the phenotypic divergence is observed from the first to the sixth generation as based on the discrimination by a linear function of nine metric traits of the wing, while, as expected, divergence is not detected on mean values and variance estimates;
differential reproductive fitness is associated with these differences and not with single traits.
It is suggested that the kind of variation observed is the outcome of a rearrangement of the developmental pattern of the wing in the population kept at different temperatures and that the reproductive fitness values are more dependent on the developmental pattern than on the genetic basis of a given character.
The results are discussed in terms of population dynamics.
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