Continent-wide differentiation of fitness traits and patterns of climate adaptation among European populations of Drosophila melanogaster

For over 100 years, the vinegar fly Drosophila melanogaster has been a workhorse for studying the genetic and phenotypic basis of evolutionary change. Ancestrally of southern-central African origin, this insect expanded its range, migrated out of Africa and colonized new habitats and climate zones around the globe. Recent population genomic analyses suggest that Europe was colonized from the Middle East ~1,800 years ago, yet we know surprisingly little about how this human commensal adapted to different locales on the European continent and elsewhere. Here, we assayed fly strains isolated from 9 European populations for 16 traits in an international consortium effort, involving >100 researchers from 26 research groups in 17 countries and using semi-standardized experimental protocols. Despite differences in experimental (environmental) conditions among labs, our trait measurements agreed well across research teams, suggesting that they are robust and generalizable. European populations of the vinegar fly are markedly differentiated for several phenotypic traits that are related to Darwinian fitness and which might be subject to natural selection. Notably, flies from locations with higher humidity and rainfall and lower temperature survive better to the adult stage, lay more eggs, are better at surviving famine and, as adults, live longer than flies from drier, warmer locations; yet, as compared to flies from warmer, drier locales, they are considerably less well adapted to surviving heat stress, suggesting a trade-off between these components of fitness. Our findings begin to illuminate how this tropical insect has adapted to different climates and habitats on the European continent and showcase the value of collaborative multi-lab studies that perform experiments in parallel.