Corticosterone response to experimental manipulation of methylation in invasive amphibian larvae

The role of epigenetic variation as a powerful driver of evolution has received increased attention in recent years. In endocrine systems, it is well-established that the methylation status of certain genes can affect the expression of hormone receptors and patterns of hormone release. For example, across taxonomic groups, epigenetic alterations have been linked to changes in glucocorticoid (GC) physiology. GCs are important metabolic hormones that influence growth/development, transition between life-history stages, and fitness. Few studies to date have examined the role of epigenetic modifications in altering phenotypic traits and fitness in wild animals. Here, we examined the effects of experimentally manipulated epigenetic status on genome-wide methylation and CORT patterns in cane toad (Rhinella marina) tadpoles. Cane toads are non-native to Australia and have rapidly expanded their range across the continent, displaying considerable variation with respect to morphology, behavior and epigenetic status. Here, we manipulated methylation via exposure to zebularine and/or predator alarm cues and examined genome-wide methylation patterns and whole animal CORT metabolites at late stages of tadpole development to determine the impacts of these treatments. In full siblings of these individuals, we examined the effects of methylation treatments on time to metamorphosis, adult morphology, and survival. We found that both treatments result in altered methylation, faster time to metamorphosis, and changes in adult morphology and survival. We discuss these results in relation to treatment-induced changes in CORT physiology and the role that epigenetics plays in rapid evolution during invasions.