Abstract
Pseudometallophytes are excellent models to study microevolution and local adaptation to soil pollution, as they can grow both on metalliferous and contrasting non-metalliferous soils. Although, there has been accumulating evidence for the effects of edaphic conditions and geographical isolation on the genetic structure of pesudometallophytes, it is still a difficult problem in evolutionary biology to assess their relative importance. In this study, we investigated the spatial patterns of genetic variability, population differentiation and genetic groups in pseudometallophyte Commelina communis with 12 microsatellite loci. Eight metallicolous and six non-metallicolous populations of C. communis were sampled from cupriferous sites and surrounding non-contaminated areas in China. Neither significant reduction in genetic diversity nor apparent founder and bottleneck effects were observed in metallicolous populations of C. communis. Based on Bayesian and Neighbor-Joining clustering analyses and a principal coordinates analysis, all sampled populations were found to be mainly separated into three genetic groups, corresponding well to their geographical locations rather than edaphic origins. Moreover, a significant and strong correlation between population genetic divergence and geographical distance were detected by Mantel test (r = 0.33; P < 0.05) and multiple matrix regression with randomization (MMRR; βD = 0.57, P < 0.01). However, the effect of copper concentration on genetic patterns of C. communis was not significant (MMRR; βE = -0.17, P = 0.12). Our study clearly demonstrated that the extreme edaphic conditions in metalliferous areas had limited effects on the genetic variability in C. communis. Geographic distance played a more important role in affecting the genetic structure of C. communis than soil composition did. In C. communis, the geographically disjunctive populations on metalliferous soils had multiple origins and evolved independently from nearby non-metallicolous populations.
Highlights
Environmental stress experienced by living organisms plays an important role in local adaptation and evolution of new species (Hoffman and Parsons, 1991; Parsons, 2005; Nevo, 2011)
An overview of geographical locations and soil characteristics for the 14 C. communis populations were presented in Table 1 and Figure 1
Our data showed that severe soil conditions at metalliferous areas did not significantly affect the levels of genetic variability in C. communis
Summary
Environmental stress experienced by living organisms plays an important role in local adaptation and evolution of new species (Hoffman and Parsons, 1991; Parsons, 2005; Nevo, 2011). Soils contaminated with high concentrations of heavy metals (metalliferous soils) are toxic and restrictive habitats for plants due to phytotoxicity (Antonovics et al, 1971; Wu, 1990; Ernst, 1996). Pseudometallophytes, i.e., species growing on both metalliferous and non-metalliferous soils have been found to be the dominant plants in heavy metal contaminated areas (Ernst, 2006). Exploring the genetic variation and differentiation between metallicolous (M) and non-metallicolous (NM) populations in pseudometallophytes provides us an ideal opportunity to understand the processes of plant local adaptation and microevolution in the context of environmental pollution (Linhart and Grant, 1996; Vekemans and Lefèbvre, 1997; Mengoni et al, 2000, 2001; Meyer et al, 2010)
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