Impacts of gene expression plasticity on expression evolution
A growing number of studies are using transcriptomic and proteomic surveys to address the long-standing debate on the role of plasticity in evolution, with contrasting results favoring the alternative hypotheses that adaptive (Fraser et al., 2014; Gleason & Burton, 2015; Li et al., 2018; Mäkinen, Papakostas, Vøllestad, Leder, & Primmer, 2016; Scoville & Pfrender, 2010; Shaw et al., 2014; Wang & Althoff, 2019) versus non-adaptive (Dayan, Crawford, & Oleksiak, 2015; Ghalambor et al., 2015; W. Ho & Zhang, 2018; Pespeni et al., 2013; Schaum, Rost, Millar, & Collins, 2013) plasticity facilitates adaptation. We recently proposed that non-adaptive plasticity dominates during the earliest stages of rapid evolution, and that adaptive plasticity may contribute to subsequent fine-tuning of phenotypes (Fischer et al., 2016a). In line with this prediction and our previous findings, we report here that the strong signature of non-adaptive plasticity in brain gene expression (89% of transcripts) observed in guppy populations in the earliest stages of adaptation to low-predation environments (Ghalambor et al., 2015) is present but weaker in long-established low-predation populations. Furthermore, within our data set, this signature of non-adaptive plasticity was more apparent in the more recently diverged Aripo lineage (80% of genes) as compared to the older Quare lineage (65% of genes). Our findings highlight the need to explicitly consider how plasticity relates to divergence throughout successive stages of adaptation in order to build a more holistic understanding of the role of plasticity in adaptation.