Abstract
The genetic diversity and structure of plant populations are determined by the interaction of three distinct processes: gene flow, genetic drift and natural selection. These processes are to some extent dependent on the mating system of plants, which in turn is largely determined by floral morphology and the level of herkogamy in particular. In this study, we used molecular markers to investigate the impact of floral morphology on genetic differentiation and structure in two closely related Centaurium species that display large variation in floral morphology across two distinct geographic regions in Europe (mainland Europe and the UK). Our results showed that genetic differences between regions and populations within regions were similar for both species, but that patterns of genetic structure largely depended on the observed variation in floral morphology. Populations of Centaurium erythraea showed higher genetic differentiation and clear isolation by distance (IBD) in mainland Europe, but limited IBD in the UK. Opposite patterns were found in Centaurium littorale, with higher genetic differentiation and significant IBD in populations sampled in the UK and lower genetic differentiation in Continental populations with no pattern of IBD. Overall, these results indicate that variation in floral morphology has a profound impact on structuring of genetic diversity, with populations displaying low levels of herkogamy showing the strongest patterns of genetic structuring and the reverse pattern in populations showing high levels of herkogamy.
Highlights
The genetic diversity and structure of plant populations are determined by the interaction of gene flow, genetic drift and natural selection, processes that are influenced by the geographic distribution of plant populations and population demography (Eckert et al 2008)
In C. littorale sampled in mainland Europe (Fig. 2A), most individuals of each population were assigned to one single cluster
When the number of clusters was set to K = 2, almost all individuals of Continental populations were assigned to both clusters, while most individuals of populations in the UK were assigned to just one cluster (Fig. 2C), suggesting that only a set of the genetic diversity present in mainland Europe was present in the UK
Summary
The genetic diversity and structure of plant populations are determined by the interaction of gene flow, genetic drift and natural selection, processes that are influenced by the geographic distribution of plant populations and population demography (Eckert et al 2008). Historical events such as glaciation or orogeny determine to a large extent the geographic ranges of plant and animal species, which in turn are determined by geographic barriers that limit or prevent further dispersal (e.g. mountains, oceans, or more recently fragmentation caused by human activities) (Slatkin 1987; Eckert et al 2008; Zhang et al 2014). A flat relationship with high variance between genetic and geographic distance can be expected when comparing selfing populations due to limited gene flow and the stochastic effects of genetic drift, even when populations are adjacent (Hutchison and Templeton 1999; Pettengill et al 2016)
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