Diversity, ecological patterns, and zoogeography of nematodes (Nematoda) in terrestrial vertebrates in the South of the Middle Volga Region, European Russia (a century-long synthesis)

This paper presents an overview of the nematode fauna in terrestrial vertebrates from the Samara Oblast (Middle Volga region). We analyzed our own and published literature data on the nematodes of amphibians, reptiles, birds and mammals covering a research period of over a century. To date, 124 nematode species from 33 families are known to infect vertebrates in the Samara Oblast. A total of 117 recorded nematode species use terrestrial vertebrates solely as definitive hosts, while five (Eustrongylides excisus, Spiroxys contortus, Streptocara crassicauda, Ascarops strongylina, Physocephalus sexalatus) use them only as intermediate and/or paratenic hosts. The remaining two species (Physaloptera clausa and Porrocaecum depressum) parasitise mammals at the larval and adult stages. Forty-one species of nematodes have an indirect life cycle, while 83 develop directly. Geohelminths predominate in the nematode fauna of mammals, reptiles, and amphibians, with the highest ratio observed in reptiles and mammals. Conversely, biohelminths dominate in birds. The ratio of geo- and biohelminths among nematodes of vertebrates strongly depends on the hosts’ lifestyle and diet. The majority of nematode species (70) were recorded in mammals. The nematode fauna associated with the avifauna comprises 36 species. The lower number of nematode species recorded in amphibians (15) and reptiles (11) compared with that in birds and mammals likely reflects the smaller number of host species studied in these groups (nine amphibian and nine reptile species vs. 100 bird and 48 mammal species), rather than an inherently poorer parasite fauna. Most of the nematodes identified in vertebrates of the Samara Oblast belong to the Palearctic faunal complex (61 species). Additionally, 34 species are cosmopolitan. The range of 22 nematode species spans the Holarctic. The geographic distribution of seven species is limited to Europe. Among the 124 nematode species found in terrestrial vertebrates in the Samara Oblast, 30 are of medical and veterinary importance as potential pathogens of dangerous helminthiases. Of these, seven species (Syphacia obvelata, Calodium hepaticum, Ascaris suum, Toxascaris leonina, Toxocara canis, Ancylostoma caninum, and Uncinaria stenocephala) are zoonotic, capable of infecting humans.