Fecundity of Cosmocerca ornata (Nematoda: Cosmocercidae) - parasite of marsh frogs Pelophylax ridibundus (Anura: Ranidae) in vivo

Fecundity of the Cosmocerca ornata (Dujardin, 1845) females from marsh frogs was studied in vivo. The main factor influencing the nematodes fecundity in utero, is the environmental (ambient) temperature, which is known to determine the body size of the C. ornata females. The significant influence of the water temperature on fecundity of nematodes was reliably established. The dependence of the C. ornata fecundity on the female body size and the number of nematodes in the intestine of the host was revealed. The larger C. ornata females had the higher fecundity. Nematodes fecundity was reduced with the increasing of the adult C. ornata hemipopulation density. Significant differences in the nematode fecundity depending on the age and sex of the host and the season (May-October) were observed. With the increase of the age of the host, average nematode fecundity index decreases due to the growing density of the adult C. ornata hemipopulation and the according reduction of average body size of the parasites in the older age groups of amphibians. Sex of the marsh frogs affects nematode fecundity only during the breeding season of amphibians (May and June). During this period the C. ornata fecundity in frog males is significantly lower than in females. Seasonal differences of the C. ornata fecundity are determined by the different rates of growth and maturation of the nematodes, which in turn are regulated by the temperature factor, and seasonal differences in the ecology and physiology of amphibians (especially during the breeding season). The study of nematode fecundity in marsh frogs of the both striata and non-striata phenotypes showed no differences.