RAPID EVOLUTION OF THERMAL TOLERANCE AND GENOMIC DIVERGENCE DURING THE INVASION OF A PROLIFIC NON-NATIVE RED SEAWEED, Gracilaria vermiculophylla
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Flanagan, Benjamin Allen
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Abstract
Biological introductions have rapidly increased during the 20<sup>th</sup>
century and can negatively impact recipient communities by homogenizing
biodiversity. Commonly, colonization success has been attributed to ecological
and demographic processes, such as high growth rates or reproductive output. Recently,
evidence suggests responses to the novel non-native environment through rapid evolutionary
change(s) likely facilitates invasion success. Here, we used the widespread marine
invader, <i>Gracilaria vermiculophylla </i>to
study the role rapid adaptation plays in facilitating invasions. We observed
rapid evolution in thermal tolerance and evaluated genome-wide evolutionary changes
associated with the invasion. By exposing native and non-native thalli to
extreme temperature and observing survival, we found non-native thalli have rapidly
evolved higher thermal tolerance compared to native thalli. Additionally, by performing
a targeted expression analysis, we observed non-native thalli induced two heat-shock
proteins (Hsps) to higher levels than native thalli, suggesting a molecular
mechanism underlying the rapid phenotypic shift in thermal tolerance. We also
used Hsp inhibitors to arrest Hsp molecular function and these inhibitors
compromised the ability of thalli to survive heat stress. To evaluate genome-wide
evolution, we used genotype-by-sequencing techniques to identify approximately 9,000
single-nucleotide polymorphisms. We identified highly divergent loci between
the invasion source region of northeastern Japan and non-native genetic subregions.
The results suggest both neutral and non-neutral evolutionary processes shaped
the invasion, but neutral evolutionary forces dominated. The combined
phenotypic and genomic work of my thesis advances our understanding of the role
rapid evolution plays in facilitating successful invasions.