Genetic evidence for founder effects in the introduced range of houndstongue (Cynoglossum officinale)
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Phenotypic differentiation can occur between the native and introduced ranges of a species as a result of novel selective pressures, or by neutral processes and historical events. Our aim was to determine how underlying patterns of genetic diversity and potential population origin might have contributed to phenotypic differentiation between the native and introduced ranges of an herbaceous weed. We combined data from microsatellite markers from 16 native and 16 introduced populations of Cynoglossum officinale, a noxious weed of the western US, with previously published phenotypic data from common gardens to investigate genetic diversity in both ranges and relate population structure to phenotypic differentiation. Several lines of evidence suggest loss of genetic diversity during the introduction of C. officinale. Despite reduced diversity, introduced plants out-performed natives in a common garden in one environment. We found little evidence that population-level variation in diversity contributed to phenotypic variation (e.g. through inbreeding depression). Our results suggest that establishment, spread, and potentially adaptation of a species to a new range is not prevented by reductions in genetic diversity of the magnitude we observed. Further, we suggest that non-random filtering or biased introduction at the point of emigration may contribute to phenotypic divergence between ranges.
KeywordsCommon garden Cynoglossum officinale Founder effects Genetic diversity Houndstongue Invasive plant Native and introduced ranges Weed
We thank Jennifer Andreas, Harald Auge, Tom de Jong, and Stefan Toepfer for collecting seeds, and Samantha Campbell for assisting in the greenhouse. We are grateful to Camille Barr for invaluable advice in the lab and to Mike Schwartz for statistical advice. Jake Alexander, Darren Johnson and Joanna Kelley provided helpful comments on the manuscript. Support for this study was provided by NSF grant DBI-0321329 to LF and to JW by an NSF Graduate Research Fellowship, NSF Doctoral Dissertation Improvement Grant DEB 05-08102 and from the National Center for Ecological Analysis and Synthesis, a Center Funded by NSF (Grant #EF-0553768), the University of California, Santa Barbara, and the State of California. Seeds were imported into the US under USDA-APHIS permit 37-86531.
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