Origin of the invasive North American beaver (Castor canadensis) sampled in Western Europe

The North American beaver (Castor canadensis) has been introduced in Western Europe since 2006. Its occurrence has been recorded in Luxembourg, Rhineland-Palatinate (Germany) and Wallonia (Belgium). As Castor canadensis is a direct competitor of the Eurasian beaver, it is classified as an invasive species due to ecological niche overlap, with a notably higher reproduction rate. Its colonization is therefore a significant threat for our native Eurasian beavers and its populations should be eradicated. The origin of the North American beaver populations in Western Europe is also still unknown. The present study aimed at investigating the genetic structure and the putative origin of C. canadensis individuals collected in Western Europe. To achieve this goal, we compared their genetic characteristics with those of individuals coming from Finland, the USA and from the German zoo of Lünebach (Eifel). Our results revealed that all the individuals sampled in Western Europe show close relationships and belong to the same genetic cluster. Given their genetic link to the Eifel zoo beavers, the hypothesis of this zoo as the origin of wild C. canadensis populations in Western Europe seems the most probable. As no North American beavers have been detected in France, we can also conclude that the eradication measures implemented in Belgium, Luxembourg and Germany since 2006 seem to have been relatively efficient, thus preventing the spread of this species to other countries. However, future monitoring still has to be performed in order to confirm the total eradication of this invasive species in Western Europe.