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Urbanisation Runs In Frogs’ Blood

20.05.2005


A glance at the frog’s skin can say what kind of blood the amphibia has, the blood composition accounting for frog’s capability to get on alongside human beings. The research by the Ural ecologists has been supported by the Russian Foundation for Basic Research.



The crucial importance for the frog is in the light strip on the back along the spinal column. V.L. Vershinin, Doctor of Biology, specialist of the Institute of Plant and Animal Ecology, Ural Branch of Russian Academy of Sciences, has discovered close correlation between availability of the strip, composition of its blood elements and frog’s capability to adapt to urban environment.

The amphibia, the first surface vertebrates, are extremely dependent on the environment. Nevertheless, they can bear all “delights” of urbanization: contaminated water bodies, piped brooks and massive asphalt pavement, so the researchers are trying to understand how the frogs can succeed in that. The blood, one of the most dynamic systems, is the quickest to react to any functional changes taking place in the organism. V.L. Vershinin started his effort from investigation of hematologic properties. In Ekaterinburg, the scientist has spent several years investigating the blood of three species of frogs: moorfrog (Rana arvalis), European common frog (Rana temporaria) and waterfrog (Rana ridibunda). Amphibia were caught within the first two weeks of surface life in the vicinity of water bodies, where tadpoles had developed. Depending on the level of man’s impact, the city was divided into four zones. The first zone, encumbered by multistorey blocks of flats, is almost deprived of lawns and water bodies, and the fourth zone – is a forest park, i.e. the recreaton zone of the citizens.


Having drawn blood samples from several hundreds of frogs, the researchers has come to the conclusion that various species differ from each other in terms of blood cell composition. However, there are common regularities. The frogs from urbanized regions have increased amount of phagocytes and erythrocyte precursor cells. Instead, frogs from clean places have a lot of eosinophiles. This is apparently due to parasites with which amphibia from natural populations are infected much more than urban frogs.

There is no doubt that indices of blood influence frogs’ fitness to urban environment. But the frogs differ in appearance. Some of moorfrogs and waterfrogs have a light strip on the back, and some – do not. This strip is hereditary. Thus, the analysis showed that striped variety initially have more erythrocyte precursor cells in the blood. Therefore, it is easier for striped frogs which got into unfavorable conditions to increase the erythrocyte level up to required level. It is not by chance that in the areas with high human impact, it is particularly striped forms of moorfrogs and waterfrogs that prevail. To all appearances, selection happens at early stages of development. Embryos, which are to become frogs without a stripe, perish more often.

Common European frog, which is by origin close to moorfrog, never has stripes. Obviously, it lost striation in the course of evolution. In the blood of common European frog there are initially few erythrocyte precursor cells, therefore, in contaminated areas the species has to spend a lot of energy to bring the amount of erythrocytes up to the required level. This is a disadvantageous strategy. Ecologists have repeatedly pointed out that common European frog is gradually disappearing from urbanized territories, and the striped variety of moorfrog develops these territories.

Recently, there have been multiple discussions about the necessity for preservation of diversity: biological, genetic and specific one. In V.L. Vershinin’s opinion, the data collected by him clearly demonstrate in what way diversity within the species determines successfulness of its existence. Striped frogs differ from their plain sisters by blood composition. If ecologists had not ascertained that, they would have guessed how the strip along the back helps frogs settle in contaminated urban puddles.

Sergey Komarov | alfa
Further information:
http://www.informnauka.ru

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