Transcriptional counterbalance between WGP and TGP
Our results suggest that selection for adaptive TGP targets similar genes and functions when evolving simultaneously with WGP, with 56 % or 234 overlapping genes between the two types of plasticity. However, the direction of gene expression in the majority of these genes follows opposing transcriptional trajectories in the two types of plasticity (Figure 4a). Of the 234 overlapping genes between WGP and TGP, 215 are up-regulated in TGP. Of these, 204 genes are also down-regulated in WGP (Figures 5a and 5b).
During the heat-shock response in WGP, a large portion of the cellular resources is used to induce the molecular chaperones and proteolysis genes needed to overcome periods of thermal stress at the expense of a massive down-regulation in other genes. We hypothesize that the parental acclimation in TGP represents a transcriptional counterbalance, which seems to compensate for the future decrease in gene expression during thermal stress caused by the environment in the offspring. To understand better this transcriptional counterbalance provided by parental acclimation, we followed the transcriptional trajectories of the overlapping genes between WGP and TGP across all combinations of acclimation treatments (Figure 5c). We found a strong interaction effect between the parental and offpring acclimation treatments. As expected, on average, the gene expression level in these genes is significantly down-regulated by the acclimation treatment performed in the offspring. However, it is up-regulated by the acclimation treatment performed in the parental generation (Figure 5d). More interestingly, this interaction leads to a transcriptional compensation where acclimated larvae at 36 °C whose parents were also acclimated at 36 °C show no significant differences in the level of the gene expression compared to larvae that did not receive any acclimation treatments in the parental or offspring generations (Figure 5c). This pattern of gene expression is not detected when considering non-overlapping DE genes between WGP and TGP (i.e. , WGP-only and TGP-only genes, Figure S4).