View Program - 2022 Population, Evolutionary, and Quantitative Genetics Conference

To understand the molecular mechanisms underlying complex traits in wild populations, we measured metabolic and thermal tolerance traits and related them to mRNA expression. Traits included whole animal metabolic rate (WAM), substrate specific cardiac metabolic rate (CaM; substrates= glucose, fatty acids, lactat+ketones+ethanol, and endogenous), and critical thermal maximum (CT_max) among three Fundulus heteroclitus populations acclimated to 12°C and 28°C. Populations showed few significant interpopulation differences in these traits due to large inter-individual variation. In contrast, acclimation temperature significantly affected WAM and CT_max but not CaM. Within each acclimation temperature we examined which mRNAs were related to each trait using a weighted gene co-expression network analysis. These analyses revealed 9 significant heart ME (first principal component of module expression) and 4 significant brain ME. Heart MEs explain variation in whole animal metabolism (WAM), critical thermal maximum (CT_max), and two of the four substrate specific cardiac metabolic rates at 12°C. The only heart trait related to mRNA expression at 28°C was CT_max. These patterns at 12°C and 28°C were related to the higher inter-individual variation at 12°C. Brain MEs explains CTmax and WAM at 28°C but not at 12°C. Combining MEs as multiple correlations, 82% of variation in WAM at 12°C was explained by four heart MEs, 80% of variation in FA CaM at 12°C was explained by three heart MEs, and 72% of variation in CT_max at 28°C was explained by three brain MEs. MEs significantly correlated with traits were enriched for Kyoto Encyclopedia of Genes and Genomes (KEGG) terms related to specific metabolic pathways known to impact these traits, suggesting that these MEs represent biologically relevant pathways. Together these data suggest that mRNA co-expression explains complex traits and importantly mRNA expression patterns that explain traits are different for different temperatures and tissues.

mRNA expression explains metabolic and thermal tolerance trait variation