Press release November 29th, 2007

Indigenous water frogs under threat

Angers/Leipzig. Indigenous water frogs can be crowded out by immigrant or imported species. This is the finding of a Franco-German study. The scientists investigated water frog populations in France and Northern Spain and noticed that the marsh frog (Rana ridibunda), which normally occurs only in Eastern Europe, has the potential to crowd out indigenous species like Graf’s hybrid frog (Rana grafi) and the Iberian water frog (Rana perezi).

Marsh Frog <i>Rana ridibunda</i>

The marsh frog (Rana ridibunda)
Source: Dirk Schmeller/UFZ

download as jpg (2.1 MB)

Graf’s hybrid frog (<i>Rana grafi</i>)

Graf’s hybrid frog (Rana grafi)
Source: Dirk Schmeller/UFZ

download as jpg (3.4 MB)

The scientists believe this ability is related to the fact that the marsh frog lives longer and grows faster than the indigenous species. In addition, the female marsh frogs produce more progeny than their competitors, the researchers write in the scientific journal Comptes Rendus Biologies. The marsh frog has now spread from Central Asia as far as France and Spain. This latest spread is attributed to imports of live animals for culinary purposes. As the foreign species mix with the indigenous species, the indigenous water frogs are being pushed back into just a few areas. Imports of invasive species by humans are regarded as one of the main threats to species diversity on earth, alongside climate change.

Most stable marsh frog populations in France and Switzerland originated from frogs bred for gourmet restaurants or imported directly from various source countries. The frog fauna along larger river flood plains in both countries has now altered significantly in favour of the new frog species. Until now though, it was not clear why the new species had been able to establish themselves in the face of the indigenous species. The team of scientists investigated over 700 water frogs from 22 locations in the Rhone drainage basin in France and four locations in the Ebro drainage basin in Spain. "We noticed that the introduced marsh frog has a high competitive potential, particularly in high-oxygen, low-salinity freshwater. In these conditions the indigenous frogs hardly stand a chance," declares Dr Dirk Schmeller of the Helmholtz Centre for Environmental Research (UFZ). The displacement process is linked to the fact that the marsh frog grows faster than the indigenous frogs, and is in direct competition for food. In addition, female marsh frogs live longer and are more fertile. This means that over the course of their lives they produce significantly more progeny, thereby crowding out the other frog species. The number of progeny is increased still further because when the marsh frog mates with Graf’s hybrid frog (Rana grafi) or the edible frog (Rana esculenta), it produces marsh frog progeny. This may sound astounding, but can be attributed to a special type of reproduction called hybridogenesis, which is a special feature of water frog reproduction. All these factors may lead to the extinction of the indigenous water frog species, the researchers believe, and therefore recommend that the spread of the marsh frog be closely monitored.
Tilo Arnhold


Introducing water frogs - Is there a risk for indigenous species in France?
Comptes Rendus Biologies 330: 684-690.


IUCN information about Rana ridibunda:
IUCN-Informationen über Rana ridibunda

Marsh Frog (Rana ridibunda):

Iberian water frog (Rana perezi):
Iberischer Wasserfrosch (Rana perezi

Weitere fachliche Informationen:

Dr. Dirk Schmeller
Hemholtz Centre for Environmental Research - UFZ
Phone: +49 341 235-3282
Dr. Dirk Schmeller

Station d'Ecologie Experimentale du CNRS à Moulis
09200 Saint Girons
phone 0033 5 61 04 03 73

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Hemholtz Centre for Environmental Research - UFZ
Press office
Tilo Arnhold / Doris Böhme
phone +49 (0)341 235 2278

The Helmholtz Centre for Environmental Research – UFZ was established in 1991 and has about 830 employees in Leipzig, Halle/S. and Magdeburg. They study the complex interactions between humans and the environment in cultivated and damaged landscapes. The scientists develop concepts and processes to help secure the natural foundations of human life for future generations.
The Helmholtz Association contributes to solving major challenges facing society, science and the economy with top scientific achievements in six research areas: Energy, Earth and Environment, Health, Key Technologies, Structure of Matter, Transport and Space. With 25,700 employees in 15 research centres and an annual budget of approximately 2.3 billion euro, the Helmholtz Association is Germany's largest scientific organisation. Its work follows in the tradition of the great natural scientist Hermann von Helmholtz (1821-1894).