Habitat differentiation vs. isolation‐by‐distance: the genetic population structure of Elymus athericus in European salt marshes

Abstract

We investigated genetic differentiation among populations of the clonal grass Elymus athericus, a common salt-marsh species occurring along the Wadden Sea coast of Europe. While E. athericus traditionally occurs in the high salt marsh, it recently also invaded lower parts of the marsh. In one of the first analyses of the genetic population structure in salt-marsh species, we were interested in population differentiation through isolation-by-distance, and among strongly divergent habitats (low and high marsh) in this wind- and water-dispersed species. High and low marsh habitats were sampled at six sites throughout the Wadden Sea. Based on reciprocal transplantation experiments conducted earlier revealing lower survival of foreign genotypes we predicted reduced gene flow among habitats. Accordingly, an analysis with polymorphic cross-species microsatellite primers revealed significant genetic differentiation between high and low marsh habitats already on a very small scale (< 100 m), while isolation-by-distance was present only on larger scales (60-443 km). In an analysis of molecular variance we found that 14% of the genetic variance could be explained by the differentiation between habitats, as compared to only 8.9% to geographical (isolation-by-distance) effects among six sites 2.5-443 km distant from each other. This suggests that markedly different selection regimes between these habitats, in particular intraspecific competition and herbivory, result in habitat adaptation and restricted gene flow over distances as small as 80 m. Hence, the genetic population structure of plant species can only be understood when considering geographical and selection-mediated restrictions to gene flow simultaneously.

Morphological and genetic diversity of European cranberry (Vaccinium oxycoccos L., Ericaceae) clones in Lithuanian reserves

“…By contrast, our study of V. oxycoccos populations exhibited relatively low (71%) intrapopulation genetic variation, based on RAPD. This also contrasts with our SSR results, which showed 97% genetic variability between Žuvintas and Čepkeliai populations, whereas in other vegetatively propagated clonal species it ranged from 71-86% [34][35][36].…”

Genetic structure and gene flow in an endangered perennial grass, Arctophila fulva var. pendulina

“…However, the pattern of the two distances (Figure 2) suggests that the significant correlation is only due to pairwise distances between the most isolated KEM and the other subpopulations, and in fact there is not association between geographic and genotypic correlations when the distance is less than 1000 m. Isolation-by-distance has been reported in other coastal an marine species. Bockelmann et al (2003) found a weak (r=0.308) but significant correlation between pairwise U ST -values and geographical distances in a grass species, Elymys athericus. In Zostera maritima a strong correlation between pairwise distances among eight European populations was revealed by Reusch et al (2000), even though no such pattern was found among Canadian populations.…”

Markers associated with altitude and ecological factors in hexaploid Campeiostachys nutans (Griseb.) J. L. Yang, B. R. Baum et C. Yen and tetraploid Roegeneria nutans (Keng) Keng

“…Differences in the sampling strategies can lead to conflicting conclusions regarding the relationship between the genetic distances and the geographical origins of the samples. Self-fertilization and limited seed dispersal can significantly influence the genetic diversity and differentiation over widely dispersed ([60 km) Elymus populations (Bockelmann et al 2003). To explore the vertical changes in population genetics, rather than the horizontal changes, sampled C. nutans and R. nutans populations from a large a range of altitudes (1,200 m) within a restricted range of latitudes (\50 km horizontally).…”