Transcriptomic\nand\nMethylomic Analyses Show Significant\nShifts in Biosynthetic Processes and Reduced Intrapopulation Gene\nExpression Variance in PAH-Adapted Atlantic Killifish

Environmental\ncontaminants pose a significant selection\npressure\nacross taxa, potentiating evolved resistance to chemicals. However,\nrapid evolution may alter molecular and physiological homeostasis\nleading to trade-offs. To elucidate molecular underpinnings of evolved\nchemical resistance, we compared liver gene expression and methylation\nprofiles in polycyclic aromatic hydrocarbon (PAH)-adapted Atlantic\nkillifish (Fundulus heteroclitus) in\nthe Republic site (RP), Elizabeth River, Virginia with PAH-sensitive\nKings Creek (KC) fish. We found 1607 differentially expressed and\n2252 alternatively spliced genes between RP and KC, with highly enriched\ngenes involving lipid and amino acid metabolism, respectively. While\n308 genes had differentially methylated regions, only 13 of these\ngenes were differentially expressed. The aryl hydrocarbon receptor\n2b gene (<i>ahr2b</i>) was differentially methylated and\nexpressed, as well as alternatively spliced signifying its critical\nrole in mediating PAH tolerance. Notably, the intrapopulation coefficient\nof variation (CoV) was lower in 82% of 17,566 expressed genes in RP\nfish compared to KC fish. Among other pathways, these genes with low\nCoV were highly enriched in bioenergetic processes inferring reduced\nmetabolic physiological variation as a population in RP fish. Altered\nmetabolic gene expression and overall reduced gene expression variance\nin RP fish warrant further studies on fitness trade-offs including\naltered susceptibility to other stressors associated with rapid adaptation\nto anthropogenic pressures.