Morphological, acoustic and genetic identification of Xenopus laevis (Anura, Pipidae) in Belgium

The African clawed frog (Xenopus laevis) is an aquatic invasive species of amphibian imported from South Africa for medical research and aquarium pet trade. Released from capture, on purpose or by accident, an invasive spread of Xenopus laevis to natural ecosystems was registered on most continents. In the absence of natural predators, their population densities can increase quickly causing damage to local aquatic ecosystems.

Using external morphology of adults and tadpoles, osteology from high-resolution microcomputed tomography, vocalization analysis and DNA sequence data, this study assessed the identity of a reproducing Belgian Xenopus population  at the current northernmost edge of the distribution of the genus in Europe.

Morphological analysis of adult and tadpoles indicates that the Xenopus population from Comines-Warneton belongs to the species Xenopus laevis. Genetic analysis indicates two

phylogeographic lineages of South African origin invading France, one originating from northern South Africa and Rooikrantz Dam and the other originating from the south-western Cape.

In the laboratory four males and two females were housed together in a large tank. At night a short series of calls was recorded. These calls are typically produced within male-male interactions. However these sounds were not able to give more information on the identity of these specimens.

Given the relative isolation of the Belgian pond, the abundance of Xenopus laevis in the pond, and the presence of tadpoles as well as subadults and large adults, it is certain that X. laevis has been present since several years. Most likely surrounding streams and ponds are also housing them.