Taxonomia integrativa de trematódeos encontrados em moluscos límnicos e quelônios do Estado do Piauí, Brasil

Abstract

The trematodes represent a diverse group of parasitic platyhelminths, with more than 800 species reported in all classes of vertebrates in Brazil. Despite this diversity, the life cycles of these parasites, which necessarily involve a molluscs as an intermediate host, are not known for most species. This gap in knowledge is even more significant when considering trematode parasites of chelonians, which are represented by more than 60 species in the country, all of which have an unknown life cycle. In the Brazilian semiarid region, some studies have reported the presence of trematode larvae associated with freshwater molluscs. However, studies aimed at advancing the identification of these parasites are non-existent. The main objective of this study was to evaluate the transmission of trematodes by mollusks in water bodies in four locations in the state of Piauí and to try to obtain adult trematode specimens from chelonians in order to associate them with their larval stages. The malacological collections (n= 29) were carried out in four municipalities (Parnaiba, Pedro II, Picos and Teresina) from March 2022 to February 2023. In addition, 15 specimens of bearded terrapins, Phrynops geoffroanus, were collected and assessed for trematode infection. 9,862 specimens of limnic mollusks belonging to the following species were collected and evaluated: Anodontites sp., Biomphalaria glabrata, Biomphalaria straminea, Drepanotrema cimex, Melanoides tuberculata, Pomacea sp., and Stenophysa marmorata. Melanoides tuberculata was the most abundant species (n= 4,174), followed by B. straminea (n = 2,977), which was the most widely distributed species among the collection points (93.75%) and the one with the highest rate of infection with trematode larval (45.45%). The species with the smallest distribution was B. glabrata, with 22 specimens collected in Bebedouro Lagoon, in the municipality of Parnaíba, followed by Anodontites sp., with 4 specimens found in Cabrinha Lagoon, in Teresina. Of the total of molluscs evaluated, 99 (1%) were found to be infected by trematode larval, found in all the localities evaluated and in 24 of the 29 collections made. A total of 30 cercarial morphotypes were found, 11 of which samplings were selected for more detailed studies involving morphological and molecular characterization. In relation to the chelonians, 37 specimens of adult trematodes belonging to the same species were recovered, which were found in the small intestine one of animal collected. Morphological and morphometric analyses of the cercariae and adult parasites obtained were carried out under an optical microscope. In addition, genetic sequences of the 28S, ITS, cox-1 and nad-1 molecular markers were obtained for the parasites collected and used for identification and phylogenetic analysis. This integrative taxonomic approach revealed the occurrence of 11 species of trematodes in the hosts analyzed. The greatest diversity of trematodes was found in Biomphalaria straminea, the intermediate host of five species (Prionosomoides scalaris, Echinostomatidae gen. sp.1, Echinostomatidae gen. sp. 2, Halipegus sp. and Atamatamidae sp.), followed by Stenophysa marmorata, host of three species (Echinostomatidae gen. sp. 3, Echinostomatidae gen. sp. 4 and Posthodiplostomum sp.). Drepanotrema cimex, M. tuberculata and Pomacea sp. were found to be infected by one species each (Echinostoma sp., Atamatam sp. and Baracktrematidae sp., respectively). The molecular results obtained from adult trematodes recovered from chelonians and echinostoma-like larvae found in B. straminea made it possible to elucidate the life cycle of P. scalaris, a species whose phylogenetic position was assessed for the first time. In this way, the use of the integrative taxonomy approach made it possible to characterize the occurrence of a rich trematode fauna in the state of Piauí. On the other hand, the generation of sequences considered to be references, obtained from adult specimens, for the Neotropical trematode fauna is essential for progress in the identification of cercariae found in molluscs.