Genetic diversity following demographic recovery in the insular endemic plant Galium catalinense subspecies acrispum

Abstract

Galium catalinense (Rubiaceae) is a perennial shrub consisting of two subspecies endemic to California's Channel Islands: Galium catalinense subsp. catalinense on Santa Catalina Island, and G. catalinense subsp. acrispum, a state-endangered taxon on San Clemente Island. A long history of overgrazing by introduced herbivores has contributed to population declines in G. catalinense subsp. acrispum. We surveyed 12 populations throughout the taxon's range for genetic variation using eight polymorphic microsatellite loci to determine the genetic impact of this demographic bottleneck. At the taxon level, 65 alleles were identified with an average of 8.1 alleles per locus, although many alleles were rare; the effective number of alleles per locus averaged 2.6. Expected heterozygosity was 0.550. Individual populations had between six and eight polymorphic loci, with expected heterozygosities ranging from 0.36 to 0.60, and effective numbers of alleles ranging from 1.8 to 3.5 per locus. Populations fell into three or four genetic clusters, depending on type of analysis, which may represent refugia where the populations persisted during intense herbivory. There is little evidence of genetic bottlenecks or substantial inbreeding within populations. These findings, coupled with indications of recent migration between populations, suggest that G. catalinense subsp. acrispum is currently unlikely to be endangered by genetic factors, but small population sizes make the taxon vulnerable to future loss of genetic diversity. Management strategies based on these genetic data, population sizes, and the spatial distribution of populations are discussed.

Population genetic diversity and structure of two rare vernal pool grasses in central California

“…As hypothesized, Fst levels and the Bayesian clustering results indicate that range-wide genetic structure exists, and gene flow among most isolated extant populations of both species is low, and is correlated with geographic distance. However, contrary to our hypothesis, most populations of both species exhibited high within population genetic diversity in relation to other vernal pool plants, grasses and insect pollinated plants reported in the literature (Gitzendanner and Soltis 2000;Sun and Salomon 2003;Riley et al 2010;Martin et al 2010;Fan et al 2011;Sloop et al 2011;Sloop and Ayres in press;Sloop et al in review), suggesting a low potential for suffering the detrimental effects of genetic drift and severe inbreeding. Predominant outcrossing and seed germination from a persistent soil seed bank probably facilitates the localized high genetic diversity, while the slight temporal structure we identified may indicate diverse cohorts residing in the seed bank (Sloop and Ayres in press), sampling bias or genetic drift.…”

“…This conclusion is supported by high allelic richness and heterozygosity, and very few fixed loci in either species when compared to other microsatellite studies in vernal pools species (Sloop et al 2011;Sloop and Aryes in press), and other assessments of genetic variation in plants (Gitzendanner and Soltis 2000;Sun and Salomon 2003;Riley et al 2010;Martin et al 2010;Fan et al 2011). It is also consistent with the high allozyme diversity observed within two T. greenei populations (Griggs and Jain 1983).…”

Narrow water barriers prevent multiple colonizations and limit gene flow among California Channel Island wild buckwheats (Eriogonum: Polygonaceae)

“…The average H E = 0.249 we found for Eriogonum is low compared to averages for other perennial California Channel Island species such as Riley, McGlaughlin & Helenurm, 2010). Even the most diverse populations have low neutral genetic diversity compared to other island endemics.…”

Morphological and anatomical characteristics of Artemisia absinthium var. absinthium and its Polish endemic variety A. absinthium var. calcigena

“…Endemics may be represented by units on a different taxonomical level, e.g. : species , subspecies (Riley et al 2010), variety (Kaye 1999) or even form (de Wilde and Duyfjes 2007), but on the other hand they should be clearly defined taxa (Mirek and Piękoś-Mirkowa 2009). A low taxonomical level is represented by the wormwood variety Artemisia absinthium L. var.…”