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).