Morphological variability of Oswaldocruzia filiformis (Nematoda: Molineidae) in amphibians from European Russia

Abstract

The morphological and morphometric variability of the nematode Oswaldocruzia filiformis from ten amphibian species (Pelophylax ridibundus, Pelophylax lessonae, Pelophylax esculentus, Rana arvalis, Rana temporaria, Bufo bufo, Bufotes viridis, Pelobates vespertinus, Bombina bombina and Lissotriton vulgaris) was studied. The sampling was performed during the period of 2018–2020 in fifteen localities of European Russia. We examined the following morphological features: the number of crests in mid-body level, the shape of lateral alae, the shape of cephalic vesicle, shape and structure of spicules in males, the shape and structure of male caudal bursa, the shape and structure of the dorsal ray of bursa; and the measurements of nine morphometric characteristics in nematode females and seven characters in males, subjected to variability. Significant differences in the variability of morphometric characteristics of O. filiformis of both sexes in different amphibian species and amphibians from various regions were revealed. Likewise, significant differences were revealed for most of morphometric features of O. filiformis from amphibians of the same species from different regions of Russia. The type of male caudal bursa and the structure and shape of spicules were identical in all O. filiformis males studied. Likewise, we have not found variability in the structure of the reproductive system in O. filiformis females. Variability was noted in the shape and size of the cephalic vesicle and lateral alae, in the number at the mid-body level, in the shape and structure of the dorsal rib of male caudal bursa. Differences in morphometric characteristics of O. filiformis from amphibians of the same species from different regions of Russia can be explained by the phenotypic plasticity of the species. While variations in the nematode morphology from different amphibian species are caused by the host-induced morphological variability of the parasite. Differences in the size of nematodes and their morphology in different regions of Russia studied may be caused by changes in ecological conditions in amphibian habitats. The broad morphological variability of the nematode O. filiformis increases the adaptive capabilities of the helminth and allows it to parasitize a wide range of hosts.