Craig, Paul

Climate change is a major conservation concern, especially for many cold-adapted species. The rate of warming due to climate change will likely outpace adaptive responses, and many populations will likely need to rely on phenotypic plasticity to cope with environmental warming. It is currently unclear whether plasticity in physiological responses to warming will be sufficient to offset the negative consequences of chronic environmental warming in ectotherms. I studied within-generation and transgenerational plasticity in two cold-adapted species of fishes, lake trout (Salvelinus namaycush) and brook trout (S. fontinalis), following temperature acclimation. Adults of both species were acclimated to either cold or warm temperatures and offspring were generated using a fully factorial breeding design, whereby the family thermal histories included crosses made within each temperature treatment and bidirectional crosses between temperatures. Offspring families were subdivided into two groups and acclimated to either warm or cold temperatures, so that offspring thermal experience matched or mismatched that of one or both parents. Offspring metabolic rate and critical thermal maximum during an acute thermal challenge were measured for both species. Limited transgenerational plasticity was detected in both species, but had a lesser effect than within-generationacclimation. In brook trout, the paternal contribution was greater than the maternal contribution. In lake trout, a mismatch in thermal acclimation, where the offspring were cold-acclimated but the parents warm-acclimated, resulted in elevated offspring metabolic rate without a corresponding increase in growth, suggesting that a mismatch in temperatures across generations could be detrimental to offspring. Using RNA-sequencing, transgenerational plasticity was linked to differential gene expression in the liver of lake trout offspring, in that genes were differentially expressed depending on the parental acclimation temperatures. Within-generation warm acclimation had the greatest effect on gene expression profile of offspring, with more genes differentially expressed under conditions of within-generation warm acclimation compared with transgenerational warm acclimation. Although it has been suggested that transgenerational plasticity may help to buffer the impact of warming due to climate change, my work implies that transgenerational plasticity, like within-generation plasticity, will be insufficient for these two species of cold-adapted salmonids to cope with climate change.

Author Keywords: Brook trout, Climate change, Lake trout, Phenotypic plasticity, Thermal tolerance, Transgenerational plasticity