title: Opposite environmental and genetic influences on body size in North American Drosophila pseudoobscura.
abstract: BACKGROUND
  Populations of a species often differ in key traits. However, it is rarely known whether these differences are associated with genetic variation and evolved differences between populations, or are instead simply a plastic response to environmental differences experienced by the populations. Here we examine the interplay of plasticity and direct genetic control by investigating temperature-size relationships in populations of Drosophila pseudoobscura from North America. We used 27 isolines from three populations and exposed them to four temperature regimes (16°C, 20°C, 23°C, 26°C) to examine environmental, genetic and genotype-by-environment sources of variance in wing size.
  
  
  RESULTS
  By far the largest contribution to variation in wing size came from rearing temperature, with the largest flies emerging from the coolest temperatures. However, we also found a genetic signature that was counter to this pattern as flies originating from the northern, cooler population were consistently smaller than conspecifics from more southern, warmer populations when reared under the same laboratory conditions.
  
  
  CONCLUSIONS
  We conclude that local selection on body size appears to be acting counter to the environmental effect of temperature. We find no evidence that local adaptation in phenotypic plasticity can explain this result, and suggest indirect selection on traits closely linked with body size, or patterns of chromosome inversion may instead be driving this relationship.
authors.affiliation: College of Life and Environmental Sciences, Biosciences, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE, UK. m.l.taylor@exeter.ac.uk.
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Taylor
authors.affiliation: College of Life and Environmental Sciences, Biosciences, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE, UK. a.skeats@exeter.ac.uk.
authors.forename: Alison
authors.initials: A
authors.lastname: Skeats
authors.affiliation: College of Life and Environmental Sciences, Biosciences, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE, UK. a.wilson@exeter.ac.uk.
authors.forename: Alastair J
authors.initials: AJ
authors.lastname: Wilson
authors.affiliation: Institute of Integrative Biology, University of Liverpool, Crown Street, Liverpool, L69 7ZB, UK. t.price@liverpool.ac.uk.
authors.forename: Tom A R
authors.initials: TA
authors.lastname: Price
authors.affiliation: College of Life and Environmental Sciences, Biosciences, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE, UK. n.wedell@exeter.ac.uk.
authors.forename: Nina
authors.initials: N
authors.lastname: Wedell
mesh_terms: D000818:Animals; D049628:Body Size; D007446:Chromosome Inversion; D002980:Climate; D004330:Drosophila / Q000145:classification* / Q000235:genetics / Q000502:physiology*; D005260:Female; D014644:Genetic Variation; D008297:Male; D009656:North America; D013696:Temperature; D014921:Wings, Animal / Q000502:physiology