Weak population‐genetic structure of a widely distributed nematode parasite of frogs in the western Palearctic

Blood parasites of water frogs (Pelophylax esculentus complex) from the Danube Delta, Romania

Water frogs of the genus Pelophylax host a variety of parasites, from protozoa to helminths. Among the blood parasites, representatives of Apicomplexa, Trypanosoma and Nematoda show the highest prevalence. In this study, we focused on blood parasites of water frogs living in the Danube Delta, Romania. In total, 74 individuals of P. ridibundus and eight individuals of P. esculentus from six localities were examined. Blood parasites were detected microscopically and using a molecular marker (18S rDNA). 89.77% of frogs from all investigated localities were found to be infected with at least one parasitic group, specifically with haemogregarines (84.09%), nematodes (1.14%), and trypanosomes (63.64%). The parasitemia of haemogregarines and trypanosomes differed significantly among the studied locations. There was no statistically significant difference in parasitemia between male and female hosts. However, adults were found to have a significantly higher parasitemia in comparison with subadults infected with haemogregarines. Correlation between parasitemia and the body length of frogs infected with haemogregarines was also significant (r = 0.226). By comparing the 18S rDNA sequences with the corresponding GenBank sequences, Hepatozoon species identified in water frogs showed a close similarity (98.1-99.8%) to Hepatozoon magna. Trypanosomes showed the highest sequence similarity to Trypanosoma sp. isolate R10 clone L2-3, Trypanosoma ranarum, and Trypanosoma cobitis.

Ecological Analysis and Biodiversity of the Helminth Community of the Pool Frog Pelophylax lessonae (Amphibia: Anura) from Floodplain and Forest Water Bodies

This work presents an ecological analysis of the community and biodiversity of helminths of Pelophylax lessonae (Camerano, 1882) from floodplain and forest reservoirs of the European part of Russia. The material for the work was personal collections of helminths made from 2018–2021 in the National Park “Smolny” (Republic of Mordovia). Two hundred and thirty-five amphibian specimens were examined from nine reservoirs and three types of hydrobiocoenoses: (1) floodplains of a medium-sized river (in terms of catchment area); (2) floodplains of a small river; (3) a number of isolated forest reservoirs. Twenty-four species of helminths have been registered: Trematoda (20) and Chromadorea (4). Similar features (common species of trematodes and nematodes) were determined as well as differences in the composition and structure of the helminth fauna, the level of infestation by individual species and groups of helminths, diversity, and community structure. Amphibians of the river floodplain have a richer helminth fauna, they are more infected with a large number of helminths, and their community is more complex. Amphibians of isolated forest ponds, on the contrary, have fewer helminths, they are generally less infected, and their community is simplified (reduced). Having intermediate indicators of composition, structure, and degree of infestation, frogs from the forest floodplain of the small river—differ in the most diverse and maximally evenness community of helminths. The results of the study demonstrate the influence of biotopic factors on the formation of an amphibian helminth community.