title: Evidence that natural selection maintains genetic variation for sleep in Drosophila melanogaster.
abstract: BACKGROUND
  Drosophila melanogaster often shows correlations between latitude and phenotypic or genetic variation on different continents, which suggests local adaptation with respect to a heterogeneous environment. Previous phenotypic analyses of latitudinal clines have investigated mainly physiological, morphological, or life-history traits. Here, we studied latitudinal variation in sleep in D. melanogaster populations from North and Central America. In parallel, we used RNA-seq to identify interpopulation gene expression differences.
  
  
  RESULTS
  We found that in D. melanogaster the average nighttime sleep bout duration exhibits a latitudinal cline such that sleep bouts of equatorial populations are roughly twice as long as those of temperate populations. Interestingly, this pattern of latitudinal variation is not observed for any daytime measure of activity or sleep. We also found evidence for geographic variation for sunrise anticipation. Our RNA-seq experiment carried out on heads from a low and high latitude population identified a large number of gene expression differences, most of which were time dependent. Differentially expressed genes were enriched in circadian regulated genes and enriched in genes potentially under spatially varying selection.
  
  
  CONCLUSIONS
  Our results are consistent with a mechanistic and selective decoupling of nighttime and daytime activity. Furthermore, the present study suggests that natural selection plays a major role in generating transcriptomic variation associated with circadian behaviors. Finally, we identified genomic variants plausibly causally associated with the observed behavioral and transcriptomic variation.
authors.affiliation: Department of Evolution and Ecology, University of California, 3352 Storer Hall, One Shields Ave., Davis, CA, 95618, USA. nhsvetec@ucdavis.edu.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Svetec
authors.affiliation: Department of Evolution and Ecology, University of California, 3352 Storer Hall, One Shields Ave., Davis, CA, 95618, USA. lizzhao@ucdavis.edu.
authors.forename: Li
authors.initials: L
authors.lastname: Zhao
authors.affiliation: Department of Evolution and Ecology, University of California, 3352 Storer Hall, One Shields Ave., Davis, CA, 95618, USA. psaelao@ucdavis.edu.
authors.forename: Perot
authors.initials: P
authors.lastname: Saelao
authors.affiliation: Department of Entomology and Nematology, University of California, Davis, CA, USA. jcchiu@ucdavis.edu.
authors.forename: Joanna C
authors.initials: JC
authors.lastname: Chiu
authors.affiliation: Department of Evolution and Ecology, University of California, 3352 Storer Hall, One Shields Ave., Davis, CA, 95618, USA. djbegun@ucdavis.edu.
authors.forename: David J
authors.initials: DJ
authors.lastname: Begun
mesh_terms: D000064:Acclimatization; D000818:Animals; D002980:Climate; D004331:Drosophila melanogaster / Q000145:classification* / Q000235:genetics / Q000502:physiology*; D005260:Female; D005843:Geography; D008297:Male; D023421:Models, Animal; D010176:Panama; D012641:Selection, Genetic; D012890:Sleep; D059467:Transcriptome; D014481:United States