Genetic variation and clonal structure of the rare, riparian shrub Spiraea virginiana (Rosaceae)

Abstract

Genetic diversity is often considered important for species that inhabit highly disturbed environments to allow for adaptation. Many variables affect levels of genetic variation; however, the two most influential variables are population size and type of reproduction. When analyzed separately, both small population size and asexual reproduction can lead to reductions in genetic variation, although the exact nature of which can be contrasting. Genetic variables such as allelic richness, heterozygosity, inbreeding coefficient, and population differentiation have opposite predictions depending upon the trait (rarity or clonality) examined. The goal of this study was to quantify genetic variation and population differentiation in a species that resides in a highly stochastic environment and is both rare and highly clonal, Spiraea virginiana, and to determine if one trait is more influential genetically than the other. From populations sampled throughout the natural range of S. virginiana, we used microsatellite loci to estimate overall genetic variation. We also calculated clonal structure within populations, which included genotypic richness, evenness, and diversity. Gene flow was investigated by quantifying the relationship between genetic and geographic distances, and population differentiation (h) among populations. Observed heterozygosity, genotypic richness, and inbreeding coefficients were found to be representative of high clonal reproduction (averaging 0.505, 0.1, and -0.356, respectively) and the number of alleles within populations was low (range = 2.0-3.6), being more indicative of rarity. Population differentiation (h) among populations was high (average = 0.302) and there was no relationship between genetic and geographic distances. By examining a species that exhibits two traits that both can lead to reduced genetic variation, we may find an enhanced urgency for conservation. Accurate demographic counts of clonal species are rarely, if ever, possible and genetic exploration for every species is not feasible. Therefore, the conclusions in this study can be potentially extrapolated to other riparian, clonal shrubs that share similar biology as S. virginiana.

Effects of clonality on the genetic variability of rare, insular species: the case of Ruta microcarpa from the Canary Islands

“…Support for this interpretation comes from the observation that, contrary to our results in R. microcarpa , low values of genetic diversity were found for sexually reproducing Canarian endangered species ( H e = 0.2 for Anagyris latifolia , González-Pérez et al 2009; H o = 0.113, H e = 0.306 for Lotus kunkelii , Oliva-Tejera et al 2006; H o = 0.100, H e = 0.112 for Cistus chinamadensis ssp. gomerae , Batista et al 2001), while values of genetic diversity were similar to those found in this study for other endangered clonal species such as the Canarian endemic Sambucus palmensis ( H o = 0.550, H e = 0.499; Sosa et al 2010) and the Southern Appalachian endemic Spiraea virginiana ( H o = 0.503, H e = 0.391; Brzyski and Culley 2011). …”

Dams and canyons disrupt gene flow among populations of a threatened riparian plant

“…This is different from what has been found for the riparian tree species black poplar (Smulders et al, 2008), a wind-pollinated and wind-dispersed species. Also, no isolation by distance was found in some other species (Honnay et al, 2010;Brzyski & Culley, 2011). These results are similar to those of Mitsui, Isagi & Setoguchi (2010), Kondo, Nakagoshi & Isagi (2009), Hudman & Gido (2013 and Van Looy et al (2009).…”

“…Smulders et al, 2008). Also, no isolation by distance was found in some other species (Honnay et al, 2010;Brzyski & Culley, 2011).…”

Population Structure and Genetic Diversity Within the Endangered Species Pityopsis ruthii (Asteraceae)

“…Overall, P. ruthii has high levels of diversity compared to other species, both within Asteraceae and in other families. Expected heterozygosity is considerably higher ( H E = 0.63) than that found in endemic cliff dwelling perennial species ( Opisthopappus longilobus ; H E = 0.20 and O. taihangensis ; H E = 0.14) from China ( Guo et al, 2013 ) and Spiraea virginiana ( H E = 0.39), a rare riparian shrub from the Southern Appalachian region of the United States ( Brzyski and Culley, 2011 ). Within the Hiwassee River populations, slightly higher inbreeding coefficients ( F IS ) were found in some peripheral populations and suggest a higher degree of inbreeding in these populations compared to more central populations, though analyses of chloroplast microsatellites did not show a lack of diversity in those same populations.…”