Epigenetic Potential as a Mechanism of Phenotypic Plasticity in Vertebrate Range Expansions

Abstract

During range expansions, organisms are often exposed to multiple pressures, including novel enemies (i.e., predators, competitors and/or parasites) and unfamiliar or limited resources. Additionally, small propagule sizes at range edges can result in genetic founder effects and bottlenecks, which can affect phenotypic diversity and thus selection. Despite these obstacles, individuals in expanding populations often thrive at the periphery of a range, and this success may be mediated by phenotypic plasticity. Increasing evidence suggests that epigenetic mechanisms may underlie such plasticity because they allow for more rapid phenotypic responses to novel environments than are possible via the accumulation of genetic variation. Here, we review how molecular epigenetic mechanisms could facilitate plasticity in range-expanding organisms, emphasizing the roles of DNA methylation and other epigenetic marks in the physiological regulatory networks that drive whole-organism performance. We focus on the hypothalamic-pituitary-adrenal (HPA) axis, arguing that epigenetically-mediated plasticity in the regulation of glucocorticoids in particular might strongly impact range expansions. We hypothesize that novel environments release and/or select for epigenetic potential in HPA variation and hence organismal performance and ultimately fitness.

Climate Change Impacts on Seagrass Meadows and Macroalgal Forests: An Integrative Perspective on Acclimation and Adaptation Potential

“…Epigenetic variations are molecular modifications that alter gene expression, but not the underlying DNA sequence, and occur in the form of histone modifications, non-coding RNAs, and DNA methylations (Bossdorf et al, 2008;Berger et al, 2009). Recent studies in the young research field of Ecological Epigenetics provide increasing evidence for the potential of epigenetic variation to increase plasticity, facilitate speciation and accelerate adaptation to new environments and stressful conditions (Schrey et al, 2013;Bonasio, 2015;Verhoeven et al, 2016;Kilvitis et al, 2017;Richards et al, 2017).…”

“…Seagrasses likely show methylation in the same three sequence contexts as terrestrial plants, including CHG, CHH, and CG (Xie and Yu, 2015;Kilvitis et al, 2017;Richards et al, 2017). So-called CpG islands represent clusters of CG sites in gene promoter regions, and are commonly associated with gene expression regulation (Bossdorf et al, 2008;Illingworth and Bird, 2009;Zhang and Jeltsch, 2010).…”

DNA methylation predicts immune gene expression in introduced house sparrows Passer domesticus

“…younger populations) expressed more TLR4 than individuals residing nearer to the site of introduction. We also found that house sparrows with lower TLR4 expression were more likely to be infected with malaria and coccidian parasites (Martin et al ) and that high TLR4 expression was associated with low energetic and nutrient costs of inflammation (Martin et al ). These results, collectively, indicate that more TLR4 expression is more protective and/or less costly, but given the broad scope of that previous work, we are reticent to claim that the cause of TLR4 variation among populations or individuals is known.…”

“…Already we know that variation in DNA methylation patterns are quite extensive across the geographic range of house sparrows. For example, one non‐commensal subspecies was epigenetically distinct from four commensal subspecies from the Middle East, and overall DNA methylation variation was correlated with some morphological variation (Riyahi et al ). Patterns of DNA methylation also differentiated three distinct introduction events of house sparrows into Australia (Sheldon et al 2018).…”

“…Our interest in the present study is to explore more directly whether DNA methylation might facilitate plasticity and hence allow for rapid phenotypic matching to local conditions (Kilvitis et al , Hawes et al 2018). The phenotypes of Kenyan house sparrow populations are quite variable (Liebl and Martin , 2013, 2014, Martin and Liebl , Martin et al , 2015), despite the recency of the expansion and extensive admixture (Schrey et al ).…”