that in recent historical time, i.e., Pleistocene, the geographic ranges of D. melanogaster and D. simulans were completely disjunct. Hence, the two cryptic species are assumed to have been allopatric species in the Afrotropical region, and indeed to some extent they remain so. Drosophila erectaDrosophila erecta has been recorded from the south and mid Ivory Coast: Yale at the bottom (400 m) of Mt. Nimba at the border of Guinea,

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Species distributions are often constrained by climatic tolerances that are ultimately determined by evolutionary history and/or adaptive capacity, but these factors have rarely been partitioned. Here, we experimentally determined two key climatic niche traits (desiccation and cold resistance) for 92-95 Drosophila species and assessed their importance for geographic distributions, while controlling for acclimation, phylogeny, and spatial autocorrelation. Employing an array of phylogenetic analyses, we documented moderate-to-strong phylogenetic signal in both desiccation and cold resistance. Desiccation and cold resistance were clearly linked to species distributions because significant associations between traits and climatic variables persisted even after controlling for phylogeny. We used different methods to untangle whether phylogenetic signal reflected phylogenetically related species adapted to similar environments or alternatively phylogenetic inertia. For desiccation resistance, weak phylogenetic inertia was detected; ancestral trait reconstruction, however, revealed a deep divergence that could be traced back to the genus level. Despite drosophilids' high evolutionary potential related to short generation times and high population sizes, cold resistance was found to have a moderate-to-high level of phylogenetic inertia, suggesting that evolutionary responses are likely to be slow. Together these findings suggest species distributions are governed by evolutionarily conservative climate responses, with limited scope for rapid adaptive responses to future climate change. K E Y W O R D S :Ancestral trait reconstruction, evolutionary history, niche conservatism, phylogenetic signal, species distribution, stress resistance.

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