Spatially explicit and multi-sourced genetic information is critical for conservation of an endangered plant species, San Diego thornmint (Acanthomintha ilicifolia)
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San Diego thornmint Acanthomintha ilicifolia (Gray) Gray (Lamiaceae) is a winter herb restricted to San Diego county in the United States and Baja California Norte in Mexico. Historic records document 80 occurrences of this species, with 55 extant occurrences in San Diego County currently known. We compared three measures of genetic variation to inform ongoing conservation efforts: putatively neutral genetic structure revealed from isozyme markers, apparent cytogenetic variation confirmed using flow cytometry, and potentially adaptive morphological variation quantified in a common-garden study. Together, these data indicated that this rare endemic is genetically complex, revealing significant differentiation of neutral and potentially adaptive genetic variation among populations, and possessing at least two cytotypes, sometimes even within the same population. While additional study is required to resolve the extent of potential local adaptation in this species, conservation plans should limit the movement of germplasm among occurrences and monitor populations in order to limit potential long-term impacts to population viability. Given that these findings challenge the canonical model of genetic structure in rare plants (low genetic variation and limited genetic structure), we recommend guidelines to apply genetic information to conservation strategies.
KeywordsLocal adaptation Ploidy Population genetic structure
The authors acknowledge and appreciate funding provided by the San Diego Association of Governments’ Environmental Mitigation Program (Grant Agreement #5001964), by the Center for Natural Lands Management, and by a donation from Dr. Hans and Elisabeth Spiegelberg. We thank Markus Spiegelberg, Sarah Godfrey, Patrick McConnell, and Jessie Vinje for their leadership in thornmint conservation and assistance in collecting foliage and seed samples from natural populations; Courtney Owens, Rosanna Hanson, Jody Mello, Randy Meyer, and James Boom for their assistance with laboratory technical work; and Laurie Lippitt and Stacy Anderson for managing the nursery common-garden activities. We thank Erin Conlisk, Kelly Anderson, and Burak Pekin for their for their assistance with data management and analyses of the common-garden research. We thank Michelle Labbé and Benjamin Janes for technical support in acquiring permits and property access permissions and other documents and data. We appreciate the conservation managers and regulatory agencies for protecting the wild populations of thornmint and for allowing us access and permission to sample them for this study. This paper is more robust in its content and eloquent in its presentation as a result of comments from the anonymous reviewers.
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Conflict of interest
The authors declare that they have no conflict of interest.
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