Effects of extreme temperatures on embryonic development in Drosophila species from different climates. Steven G. Kuntz¹, Michael B. Eisen^1,2. 1) Department of Molecular and Cell Biology, University of California, Berkeley, CA; 2) Howard Hughes Medical Institute, University of California, Berkeley, CA.

   Drosophila is a globally distributed genus with species living in most tropical, temperate, and subtropical climates. Although species have evolved myriad phenotypic differences, affecting pigmentation, behavior, and metabolism, their morphology is highly conserved, making the genus attractive for studying the genetic control of development. However, while conducting genome-wide analyses in embryos of diverse Drosophila species, we encountered complications arising directly from their distinct ecological niches. Most significant was the different temperatures at which each species prefers to develop and live, forcing us to compare embryos at either disparate or suboptimal temperatures. With little literature on how temperature differentially affects development in Drosophila species, we recorded time-lapse images spanning the entirety of embryogenesis of 12 geographically diverse species at precisely controlled temperatures (15C to 32.5C) and used a combination of manual and automatic curation of the resulting movies to measure when 34 developmental landmarks were reached in embryos for each species at every temperature. Tropical species from different clades exhibit similar, though not identical, temperature-dependent developmental timecourses, but two groups of temperate flies reveal unique responses to temperature extremes. D. virilis and D. mojavensis exaggerate their growth slowing when cold, while D. pseudoobscura and its close relatives arrest development from heat shock at temperatures up to 5C colder than tropical species. To investigate the effect of these developmental differences on gene expression, we have sequenced mRNA from single embryos of 5 species sampled at precise developmental landmarks at different temperatures and have identified genes relevant to environmental adaptation and genomic experiment design and analysis. Our characterization of environmental species collections will be a broadly useful Drosophila community resource.