Chapter 16

COMPARATIVE GENOMICS IN THE ASTERACEAE REVEALS LITTLE EVIDENCE FOR PARALLEL EVOLUTIONARY CHANGE IN INVASIVE TAXA

Kathryn A. Hodgins

Kathryn A. Hodgins

School of Biological Sciences, Monash University, Clayton, VIC, 3800 Australia

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Dan G. Bock

Dan G. Bock

Department of Botany, University of British Columbia, 1316-6270 University Blvd., Vancouver, BC, V6T 1Z4 Canada

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Min A. Hahn

Min A. Hahn

Department of Botany, University of British Columbia, 1316-6270 University Blvd., Vancouver, BC, V6T 1Z4 Canada

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Sylvia M. Heredia

Sylvia M. Heredia

Department of Botany, University of British Columbia, 1316-6270 University Blvd., Vancouver, BC, V6T 1Z4 Canada

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Kathryn G. Turner

Kathryn G. Turner

Department of Botany, University of British Columbia, 1316-6270 University Blvd., Vancouver, BC, V6T 1Z4 Canada

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Loren H. Rieseberg

Loren H. Rieseberg

Department of Botany, University of British Columbia, 1316-6270 University Blvd., Vancouver, BC, V6T 1Z4 Canada

Department of Biology, Indiana University, Bloomington, IN, 47405 USA

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First published: 19 July 2016
Citations: 2

Summary

Asteraceae, the largest family of flowering plants, has given rise to many notorious invasive species. Using publicly available transcriptome assemblies from 35 Asteraceae, including six major invasive species, we examined evidence for micro- and macro-evolutionary genomic changes associated with invasion. To detect episodes of positive selection repeated across multiple introductions, we conducted comparisons between native and introduced genotypes from six focal species and identified genes with elevated rates of amino acid change (dN/dS). We then looked for evidence of positive selection at a broader phylogenetic scale across all taxa. As invasive species may experience founder events during colonization and spread, we also looked for evidence of increased genetic load in introduced genotypes. We rarely found evidence for parallel changes in orthologous genes in the intraspecific comparisons, but in some cases we identified changes in members of the same gene family. Using among-species comparisons, we detected positive selection in 0.003–0.69% and 2.4–7.8% of the genes using site and stochastic branch-site models, respectively. These genes had diverse putative functions, including defence response, stress response and herbicide resistance, although there was no clear pattern in the GO terms. There was no indication that introduced genotypes have a higher proportion of deleterious alleles than native genotypes in the six focal species, suggesting multiple introductions and admixture mitigated the impact of drift. Our findings provide little evidence for common genomic responses in invasive taxa of the Asteraceae and hence suggest that multiple evolutionary pathways may lead to adaptation during introduction and spread in these species.

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