Population genetic consequences of geographic disjunction: a prairie plant isolated on Great Lakes alvars

Abstract

Species may often exhibit geographic variation in population genetic structure due to contemporary and historical variation in population size and gene flow. Here, we test the predictions that populations on the margins of a species' distribution contain less genetic variation and are more differentiated than populations towards the core of the range by comparing patterns of genetic variation at five microsatellite loci between disjunct and core populations of the perennial, allohexaploid herb Geum triflorum. We sampled nine populations isolated on alvar habitat within the eastern Great Lakes region in North America, habitats that include disjunct populations of several plant species, and compared these to 16 populations sampled from prairie habitat throughout the core of the species' distribution in midwestern Canada and the USA. Alvar populations exhibited much lower within-population diversity and contained only a subset of alleles found in prairie populations. We detected isolation by distance across the species' range and within alvar and prairie regions separately. As predicted, genetic differentiation was higher among alvar populations than among prairie populations, even after controlling for the geographic distance between sampled populations. Low diversity and high differentiation can be accounted for by the greater contemporary spatial isolation of alvar populations. However, the genetic structure of alvar populations may also have been influenced by postglacial range expansion and contraction. Our results are consistent with alvar populations being founded during an expansion of prairie habitat during the warmer, hypsithermal period approximately 5000 bp and subsequently becoming stranded on isolated alvar habitat as the climate grew cooler and wetter.

Two colonisation stages generate two different patterns of genetic diversity within native and invasive ranges of Ulex europaeus

“…Although the study of neutral genetic diversity in polyploids can be complicated by genotype ambiguity (Clark and Jasieniuk, 2011), recently developed methods have proven useful in estimating genetic diversity and how it is structured geographically (for example, Hamilton and Eckert, 2007;Marrs et al, 2008). Here, we found very congruent patterns of genetic diversity and structure between different methods.…”

“…Because allele and genotype frequencies cannot be estimated, it is not possible to use classical diversity and structure statistics, such as H and F ST . Instead we used phenotype-based methods recently developed for polyploids (Obbard et al, 2006;Falush et al, 2007) that have proven useful in comparing genetic diversity and genetic structure at microsatellite loci between regions in plant species (for example, Hamilton and Eckert, 2007;Marrs et al, 2008).…”

The influence of contemporary and historic landscape features on the genetic structure of the sand dune endemic, Cirsium pitcheri (Asteraceae)

“…and Lake Huron Tansy (Tanacetum huronense Nutt. ), suggests that this region represents the likely original site of entry for C. pitcheri as well as other dune endemics (Guire and Voss, 1963;Hannan and Orick, 2000;Hamilton and Eckert, 2007). The mosaic pattern of genetic diversity would indicate that colonization has been sporadic, particularly toward the south, with rare and erratic long-distance dispersal events (Cruzan and Templeton, 2000;Clark, 1998) associated with habitat preference having an important role .…”

Genetic Variation in Past and Current Landscapes: Conservation Implications Based on Six Endemic Florida Scrub Plants

“…More specifically, some (but not all) individual studies have shown greater intraspecific genetic variation in larger [3,[11][12][13][14][15], denser [16], or less-isolated [17][18][19][20] populations. Other patterns include lower genetic variation in degraded and logged habitats [21], clines in allele frequencies [22,23] discontinuities among geographically-separated portions of the range [18,24] or between organisms separated by landscape barriers [25], higher variation in unglaciated portions of species' ranges [26], higher genetic variation in core versus marginal populations [27][28][29][30], and differences in genetic variation between distinct habitats (prairie versus alvar) [31]. Studies considering the effects of original habitat patch size, current patch size, population area, and areas of nearby suitable habitat within the landscape on local genetic variation are less common but also show positive relationships [32,33].…”