Fundamental Evolutionary Limits in Ecological Traits Drive <i>Drosophila</i> Species Distributions

<jats:title>Adaptive Limits</jats:title> <jats:p> Species adapt to a changing environment as a result of selection acting on current genetic variation. However, the degree of variation underlying traits that can respond to selection is unclear. <jats:bold> Kellermann <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5945" page="1244" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1175443">1244</jats:related-article> ; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5945" page="1212" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1179326">Merilä</jats:related-article> ) investigated the degree of genetic variation available to fruit flies for cold and desiccation tolerance. Species from the tropics tended to have low variability for these traits, while flies from more temperate climates showed higher levels of variation. However, overall genetic variability did not differ, suggesting that the tropical species lacked the alleles that confer tolerance to these environmental extremes and restrict their potential range. </jats:p>