The parasitic system of the nematode Oswaldocruzia filiformis (Strongylida: Molineidae) in Kazakhstan

In the steppe of the Republic of Kazakhstan mature nematodes Oswaldocruzia filiformis were found in the populations of moor frogs (Rana arvalis), sand lizards (Lacerta agilis) and grass snakes (Natrix natrix). In the flood plain biotopes of the Irtysh river Os. filiformis forms simple two-member parasitic systems based only on the population of R. arvalis. In the terrace areas near flood plain of the Irtysh and in a number of biocenoses of the Kazakh Hummocks, where the areas of the frog and lizard populations overlap complex two-member parasitic systems are formed. In last case Os. filiformis plays a key role and provides from 88 to 95% of the invasion flow. Sand lizard populations control only 5–12% of the invasion flow. Optimal conditions of the formation and long-term existence of parasitic systems of Os. filiformis are present on wetted shores overgrown with dense mesophytic vegetation by some lakes, rivers, other streams of the wooded steppe with kolkis, right-bank and left-bank steppe, hillocky area of the Irtysh. The relatively high degree of contamination of R. arvalis and its main role in the parasitic system of nematodes indicates the obligate status of this host species. The subordinate value in maintaining the parasitic system, the low degree of contamination observed only with sympatry with Os. filiformis infected frogs indicates the facultative status of sand lizards. Despite such a rank, the lizard, as a less hygrophilous species, could promote the release of nematodes from ecological gutters (Ural and Irtysh rivers) into biotopes of the lake basins of the wooded steppe with kolkis and steppe.