Detecting the invasive African clawed frog (Xenopus laevis) using environmental DNA (eDNA) from aquatic samples

Policy Concern Category: Invasive species

The African clawed frog (Xenopus laevis) is a popular model organism in many laboratories and has been used for scientific and medical purposes worldwide since 1930. Following escapes and/or releases from captivity, a spread of Xenopus laevis to natural ecosystems was registered on most continents. The species displays invasive capacities and, like the American bullfrog (Lithobates catesbeianus), is a voracious eater. In the absence of natural predators, their population densities can increase quickly causing damage to local aquatic ecosystems.

Its invasive success in northern Europe is, however, limited by low winter temperatures, hindering the establishment of permanent populations. Nevertheless, due to changing climate conditions, ponds rarely freeze over completely during winter nowadays, allowing the species to expand its distribution range throughout northern Europe. Presently, Xenopus laevis has been recorded in the UK, France, Portugal and Italy.

The African clawed frog spends most of its time dug in soil or hidden beneath debris at the bottom of freshwater lakes or ponds. Because of this reclusive nature, their presence can go unnoticed for a long time. With environmental DNA (eDNA), which is DNA naturally shed by organisms, the presence of aquatic species, even elusive ones, can be detected directly from water samples without the need for collecting individuals. Using water filtering systems, the DNA can be captured, extracted and analysed.
In the framework of this project BopCo aims at detecting the African clawed frog, from freshwater bodies using eDNA and qPCR assays. Specific primers and probes are used to distinguish and detect Xenopus laevis DNA, even in extremely low concentrations. From July-September 2021 BopCo has screened certain ponds and other stagnant water bodies in Belgium to screen for the presence of the African clawed frog. Specific ponds were targeted where the presence of Xenopus laevis is suspected following observations made by citizens.

BopCo Coordinators: Sophie Gombeer, Nathalie Smitz, Kenny Meganck & Ann Vanderheyden

Publications & Presentations:

Partners & Collaborators: Olivier Pauwels (RBINS) and Jonathan Brecko (RBINS)

Pictures:

• African Clawed Frog (Xenopus laevis) By Josh More [CC BY-NC-ND 2.0]
• Xenopus laevis_albino_dark_var By Nathalie Smitz
• Xenopus laevis By David J Stang [CC BY SA 4.0]
• Xenopus laevis_var_albino By Kenpei I [ CC BY SA 3.0]