Evolution of expression plasticity
We next explored the evolution of expression plasticity itself. We identified genes with evolved expression plasticity as those in which the direction and/or degree of plasticity depended on population of origin, i.e. those genes with significant population-by-rearing interaction effects. The number of genes with significant expression plasticity that evolved (i.e. significant rearing and interaction effects) was approximately a quarter to a third of the number of genes with significant expression plasticity that did not evolve (i.e. significant rearing effect but not interaction; 263/1,118 in Aripo, 286/791 in Quare) (Fig. 2).
To characterize how expression plasticity evolved, we further subdivided genes with significant population-by-rearing interaction effects into one of five categories: assimilated, accommodated, reversed, evolved plastic, or unclassified (Fig. 4A; based on Renn and Schumer, 2013). We found many transcripts that exhibited evolution of plasticity, with all five categories represented in both datasets (Fig. 4B). In the Aripo drainage 263 (32%) transcripts showed patterns of expression assimilation, 81 (10%) transcripts showed patterns of expression accommodation, 113 (14%) transcripts exhibited reversed plasticity, and 182 (22%) transcripts evolved plasticity in the derived population. In the Quare drainage, 164 (28%) transcripts showed patterns of expression assimilation, 110 (19%) transcripts showed patterns of expression accommodation, 128 (22%) transcripts exhibited reversed plasticity, and 95 (16%) transcripts evolved plasticity in the derived population (Fig. 4B).