Introduced from Africa: The clawed frog was once used in European pharmacies for pregnancy tests – now it is found in nature. Its invasive potential is more threatening than expected, researchers are now reporting: Their new approach to assessing the suitability of habitats shows that the possible dispersal areas in Europe are twice as large as previously assumed. According to this, the clawed frogs could conquer many more areas in southern and western Europe and the problematic amphibians could also threaten the ecosystems in parts of Germany.
Beyond its South African homeland, the clawed frog (Xenopus laevis) mainly due to its use as a “living pregnancy test”. Until the 1960s, urine samples from women were injected into female animals. If they contained pregnancy hormones, the frogs then produced eggs within just one day. This use as a detection system gave the amphibian, which is easy to keep in aquariums, the nickname pharmacist frog. Even today, the clawed frog, up to 13 centimeters in size, is still a popular test animal in various research areas.
From pharmacist frog to problematic conqueror
But its spread outside of his native Africa now extends far beyond the laboratories. Escaped or abandoned clawed frogs have been able to establish themselves in the wild in many parts of the world. In Europe, populations in France, Italy and Portugal are known. As food competitors and predators in these countries, they cause great damage to the local ecosystems. In addition, the clawed frog is considered to be the carrier of the chytrid fungus, which is deadly for many amphibians (Batrachochytrium dendrobatidis), which is considered to be one of the main causes of global amphibian extinction. The clawed frog is insensitive to infection with the pathogen. This allows him to spread it particularly intensely.
But what will happen next – to what extent has the clawed frog already exhausted its potential to spread in Europe? Previous forecasts based on models for estimating
Areas that are suitable for expansion due to their conditions showed a comparatively small potential. But as the results of the researchers led by Philipp Ginal from the Koenig Zoological Research Museum in Bonn show, the risk is far underestimated. “With our new approach, we were able to determine the critical minimum, maximum and optimal temperatures under which the frog can survive through laboratory tests,” explains Ginal the new procedure. His colleague Dennis Rödder continues: “Thanks to the innovative methodical approach, it was even possible to feed the physiological limits of various developmental stages, such as tadpoles and adult frogs, into the model, which was also not possible before,” explains the scientist.
Plenty of room for expansion
The results show that in Europe large areas are suitable for the clawed frog. The previous methodological approaches, on the other hand, had only suggested a maximum of half the area. According to the researchers’ models, southern and western Europe in particular are particularly suitable for the amphibian. But isolated areas in Germany also seem to meet the climatic requirements of the frog. To illustrate the reliability of their model, the scientists also fed climatic data from southern Africa into their calculation system. They were able to show that the theoretically predicted suitability of habitats in Africa corresponds to the natural distribution of the clawed frogs in their original homeland.
According to the researchers, the results shed new light on the assessment of the clawed frog’s risk of invasion. As they finally report, their assessments seem to be reflected in signs that the invasive frogs are currently spreading rapidly, especially in France. In future studies, the scientists are now planning to explore the further adaptability of these animals to the European climate. This could show the threat potential more clearly and possibly lead to measures that contain the advance in Europe better than before.
Source: Koenig Zoological Research Museum, specialist article: Journal of Experimental Zoology Part A Ecological and Integrative Physiology, doi: 10.1002 / jez.2432