MECHANISMS OF INVASIVE RANGE EXPANSION: PLASTICITY, GENETIC VARIATION, AND EPIGENETIC VARIATION IN A CLONAL SPECIES
Madrid Thorson, Jennifer Lorraine
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Adaptation to novel and changing environmental conditions is crucial for the persistence and range expansion of species in the context of biological invasions and climate change. Investigating the mechanisms by which populations adapt to environmental conditions is a key component of our understanding of adaptive evolution. Invasive species are prime candidates to study these mechanisms of adaptation. I have examined several mechanisms facilitating adaptation in a widely invasive and asexual aquatic snail, Potamopyrgus antipodarum. Classically, adaptation is attributed to selection on phenotypic variation which is encoded by genetic variation. I have investigated an assemblage of clonal lineages of P. antipodarum to understand how these clonal lineages respond to diverse habitats in the invasive range. The clonal lineages sampled represent habitat generalists, appearing in multiple diverse habitats. Phenotypic plasticity involves environmentally driven alterations to the phenotype independent of the genotype and is understood to be common and important among invasive species. I have examined the origins of phenotypic plasticity among invasive populations to understand if the trait of plasticity precedes an invasion event or if plasticity is a response to the novel range. The invasive lineages exhibited alterations in the reaction norm, supporting the hypothesis that invaders adapt through shifts in phenotypic plasticity. Finally, the alteration of methylation of DNA sequences can lead to shifts in levels of gene expression, which can result in phenotypic variation independent of genetic variation. I have quantified the variation of methylation among phenotypically diverged populations of the invader to understand if epigenetic variation is a mechanism that can explain adaptive phenotypic change among populations. Significant differences in the methylation of the two divergent populations support the potential for epigenetic alterations to facilitate rapid adaptation.