Genetic structure of the European white elm (Ulmus laevis Pall., Ulmaceae) in Switzerland

Abstract

Key message Populations of the European white elm (Ulmus laevis Pall.) in Switzerland can be considered natural. They show no evidence of genetic differentiation from other European populations. In the past, the U. laevis populations were probably more widespread and continuous in Switzerland with a larger gene flow. Context In Switzerland, at the margin of its distribution range, U. laevis is rare and considered endangered. Whether the species is native to Switzerland has been disputed, and it is often surmised to be solely cultivated, without any natural population in the country. Aims The structure of genetic diversity among Swiss populations of U. laevis and comparison to European populations are expected to shed light on the origin of local populations and support their management. Methods We analyzed 19 populations (194 individuals) in Switzerland and 15 populations (158 individuals) from other European countries, using a set of five microsatellite loci. Results (1) 90% of the genetic variation in European and Swiss populations occurs within populations. (2) We did not detect isolation by distance at the regional or continental scale. (3) Clustering analysis did not reveal any spatial pattern in the level of admixture of individuals within Swiss or other European populations. Conclusion Moderate levels of genetic diversity and evidence for recent gene flow between populations indicate that habitat deterioration, loss, and fragmentation are the main threats to the persistence of U. laevis populations in Switzerland.