The ability of sensitive rainforest species to evolve in response to climate change is largely unknown. We show that the Australian tropical rainforest fly Drosophila birchii exhibits clinal variation in desiccation resistance, but the most resistant population lacks the ability to evolve further resistance even after intense selection for over 30 generations. Parent-offspring comparisons indicate low heritable variation for this trait but high levels of genetic variation for morphology. D. birchii also exhibits abundant genetic variation at microsatellite loci. The low potential for resistance evolution highlights the importance of assessing evolutionary potential in targeted ecological traits and species from threatened habitats.

Pigmentation is a classic phenotype that varies widely and adaptively in nature both within and among taxa. Genes underlying pigmentation phenotype are highly pleiotropic, creating the potential for functional trade-offs. However, the basic tenets of this trade-off hypothesis with respect to lifehistory traits have not been directly addressed. In natural populations of Drosophila melanogaster, the degree of melanin pigmentation covaries with fecundity and several other fitness traits. To examine correlations and potential trade-offs associated with variation in pigmentation, we selected replicate outbred populations for extreme pigmentation phenotypes. Replicate populations responded rapidly to the selection regime and after 100 generations of artificial selection were phenotyped for pigmentation as well as the two basic fitness parameters of fecundity and longevity. Our data demonstrate that selection on pigmentation resulted in a significant shift in both fecundity and longevity profiles. Selection for dark pigmentation resulted in greater fecundity and no pronounced change in longevity, whereas selection for light pigmentation decreased longevity but did not affect fecundity. Our results indicate the pleiotropic nature of alleles underlying pigmentation phenotype and elucidate possible trade-offs between pigmentation and fitness traits that may shape patterns of phenotypic variation in natural populations.