Genetic analysis reveals human-mediated long-distance dispersal among war cemeteries in Trifolium micranthum
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Many grassland plant species have limited capacity to disperse their seeds beyond local boundaries by natural means. Meanwhile, various forms of human transportation are observed to provide long-distance dispersal. However, the contribution of human-mediated dispersal to the spatial dynamics of established (meta)populations on the regional scale has only scarcely been addressed. Trifolium micranthum is a very small legume that is rare in western Belgium. It is found (i) inland, as a lawn weed on war cemeteries that are managed by the Commonwealth War Graves Commission, and (ii) in coastal grasslands that are managed for conservation. These stations lie over 30 km apart, though interestingly, a number of satellite war cemeteries are found within the vicinity of the coastal reserves, and these also harbor T. micranthum. We have sampled plants from these populations to study their affinities through genetic analysis (AFLP). Results indicated that the coastal cemetery populations were closely related to the inland cemeteries and not to the coastal reserves. This most likely is the result of exchange of seeds with composted lawn material among regions, whereas mowing machinery and livestock may effectuate frequent dispersal within regions. Assignment tests nonetheless indicated limited genetic admixture to have taken place at the coastal cemeteries. Thus, human management is responsible for the realization of gene flow among these remote gene pools. Human-mediated long-distance dispersal is likely to play a role in the local or regional dynamics of many other native plants, including more common and well-dispersing species.
KeywordsAnthropochory Regional ensemble Spatial genetic structure Gene flow Landscape genetics Amplified fragment length polymorphism
We sincerely thank the people of the Commonwealth War Graves Commission, for their valuable information and their kind permission to pick their ‘weeds’. We are equally indebted to the people from the Nature & Forest Agency for their support in locating and sampling plant specimens in their reserves. We further wish to acknowledge the team of the Laboratory for Genetic Analysis from the Research Institute for Nature & Forest for their thorough preparation and analysis of plant samples. We also thank Hans Matheve for assistance with the figures, and three reviewers for providing valuable comments on a former version of this manuscript.
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