Abstract
BackgroundOrganisms can rapidly adapt to their environment when colonizing a new habitat, and this could occur by changing protein sequences or by altering patterns of gene expression. The importance of gene expression in driving local adaptation is increasingly being appreciated, and cis-regulatory elements (CREs), which control and modify the expression of the nearby genes, are predicted to play an important role. Here we investigate genetic variation in gene expression in immune-challenged Drosophila melanogaster from temperate and tropical or sub-tropical populations in Australia and United States.ResultsWe find parallel latitudinal changes in gene expression, with genes involved in immunity, insecticide resistance, reproduction, and the response to the environment being especially likely to differ between latitudes. By measuring allele-specific gene expression (ASE), we show that cis-regulatory variation also shows parallel latitudinal differences between the two continents and contributes to the latitudinal differences in gene expression.ConclusionsBoth Australia and United States were relatively recently colonized by D. melanogaster, and it was recently shown that introductions of both African and European flies occurred, with African genotypes contributing disproportionately to tropical populations. Therefore, both the demographic history of the populations and local adaptation may be causing the patterns that we see.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3333-7) contains supplementary material, which is available to authorized users.
Highlights
Organisms can rapidly adapt to their environment when colonizing a new habitat, and this could occur by changing protein sequences or by altering patterns of gene expression
Parallel differences in gene expression between tropical and temperate populations on different continents We find evidence of reciprocal latitudinal differences in gene expression in the United States and Australia (Fig. 1b)
We tested for latitudinal differences in expression by looking for an excess of genes that had significantly different expression levels between latitudes in at least one continent and that tended towards the same direction on both continents
Summary
Organisms can rapidly adapt to their environment when colonizing a new habitat, and this could occur by changing protein sequences or by altering patterns of gene expression. It is common to find across many species that body size is smaller nearer the tropics, and this is associated with increases in environmental temperature [4] Direct evidence that such clines are driven by adaptation has come from reciprocal transplant experiments showing reduced fitness at different latitudes [5] and from an understanding of the function of the phenotypic differences in different environments. In Drosophila melanogaster there is clinal variation of phenotypic traits along the east coasts of Australia and the United States [8, 9] Despite these areas having only been colonized in the past few hundred years, in many cases parallel clines occur on the two continents. In some cases the genetic basis if these phenotypic differences is known, and the polymorphism has been found to vary
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