Fig. 1

Parallel differences in total gene expression between temperate and tropical populations in Australia and the United States. a Temperate (blue) and tropical or sub-tropical (red) populations were sampled from Victoria and Queensland in Australia (circles) and Maine and Florida in the United States (triangles). b Mean per gene log₂ fold expression differences between tropical and temperate populations were estimated separately for each continent. Genes that are significantly differentially expressed on either continent (FDR < 0.20) are shown in black, and the number of significant points in each quadrant is shown in the corner. Warmer colours indicate a greater density of superimposed points. c GO term enrichment was performed on genes that showed evidence for parallel differences between latitudes on both continents (FDR < 0.20 on one continent and the same direction of change in the other continent, N = 139 genes). Significant biological process categories are shown horizontally and genes in those categories vertically (p < 0.001; indicated by black squares). Red in the bottom bar indicates genes upregulated in tropical populations and blue indicates genes upregulated in temperate populations. The map was created using the R package maps