Epigenetic Variation May Compensate for Decreased Genetic Variation with Introductions: A Case Study Using House Sparrows (Passer domesticus) on Two Continents

Abstract

Epigenetic mechanisms impact several phenotypic traits and may be important for ecology and evolution. The introduced house sparrow (Passer domesticus) exhibits extensive phenotypic variation among and within populations. We screened methylation in populations from Kenya and Florida to determine if methylation varied among populations, varied with introduction history (Kenyan invasion <50 years old, Florida invasion ~150 years old), and could potentially compensate for decrease genetic variation with introductions. While recent literature has speculated on the importance of epigenetic effects for biological invasions, this is the first such study among wild vertebrates. Methylation was more frequent in Nairobi, and outlier loci suggest that populations may be differentiated. Methylation diversity was similar between populations, in spite of known lower genetic diversity in Nairobi, which suggests that epigenetic variation may compensate for decreased genetic diversity as a source of phenotypic variation during introduction. Our results suggest that methylation differences may be common among house sparrows, but research is needed to discern whether methylation impacts phenotypic variation.

Epigenetics in natural animal populations

“…In most wild animal populations examined to date, there has been an excess of DNA methylation variation relative to genetic variation (Massicotte et al, 2011;Mor an & P erez-Figueroa, 2011;Liu et al, 2012;Massicotte & Angers, 2012;Schrey et al, 2012;Liebl et al, 2013;Skinner et al, 2014;Wenzel & Piertney, 2014). First investigations into epigenetic variation in wild animal populations involved the salmonid, Oncorhynchus mykiss (Blouin et al, 2010).…”

“…clonal fish, Massicotte et al, 2011;Massicotte & Angers, 2012) or bottlenecks following invasion (e.g. house sparrows, Schrey et al, 2012;Liebl et al, 2013). Following from classic investigations in plants (Cubas et al, 1999;Kalisz & Purugganan, 2004), these studies provide the first indications from animals that DNA methylation may sometimes act independently from underlying genetic variation, and facilitate a clearer evaluation of the consequences of epigenetic variation.…”

Overcoming maladaptive plasticity through plastic compensation

“…Just as a population may contain standing genetic variation for plasticity, it could also carry standing epigenetic variation (SEV) for plasticity (e.g. Wong et al, 2005;Johannes et al, 2009;Schrey et al, 2012), with SEV being caused by variation in individuals' past experiences of their environment. A population exposed to a novel environment may therefore be phenotypically similar to its ancestral population, but have reduced variation in SEV for the loci involved.…”

Epigenetic inheritance in apomictic dandelions : stress-induced and heritable modifications in DNA methylation and small RNA

“…Several studies in natural populations of plant and animal species revealed correlations between genome-wide patterns of DNA methylation with environmental variation (Paun et al 2010;Schrey et al 2012;Schulz et al 2014Raj et al 2011;Hafer et al 2011;Dombrovsky et al 2009;Richards et al 2012;Lira-Medeiros et al 2010). Also chapter 5 of this thesis has revealed some regional differentiation in the epigenetic profiles in natural populations of apomictic dandelions.…”

“…Studies in natural populations of sexually reproducing plants demonstrated a correlation between genetic and epigenetic markers while a proportion of epigenetic variation showed sequence-independent differentiation Herrera & Bazaga 2010;Schulz et al 2014). Also in natural populations of animal species and in nectar inhabiting yeast some evidence for distinct and ecologically relevant epigenetic patterns was found Schrey et al 2012). Our study differs from these and related studies because our study was not based directly on field-collected material (or vegetatively derived offspring), but on natural DNA methylation variation that persists through apomictic seed production.…”