Morphological and molecular characterization of brown-banded broodsacs and metacercariae of Leucochloridium (Trematoda: Leucochloridiidae) parasitizing the semi-slug Omalonyx unguis (Succineidae) in Argentina.

Trematodes of the genus Leucochloridium exhibit an unusual transmission strategy among mollusks (intermediate host). The fully developed sporocyst, housing encysted metacercariae, displays vivid coloration and rhythmic activity in the snail's tentacle, mimicking insect larvae. These strategies attract insectivorous birds, their final hosts, thereby increasing the chances of completing their life cycle. In South America, the reports of adults and larval stages of Leucochloridium are scarce. Brown-banded broodsac of Leucochloridium sp. were obtained from Omalonyx unguis collected in a shallow lake from Corrientes Province, Argentina. Here, we morphologically characterized the larval stages (broodsac and metacercaria), identified the parasite through DNA sequences from nuclear 28S-rRNA (28S) and the mitochondrial cytochrome c oxidase I (COI) genes, and explored its evolutionary affinities with the Leucochloridium species available in GenBank. The present broodsac displays brown bands, with a yellowish background in the first two-thirds and yellowish-white in the last third. Based on morphological comparisons, the broodsac and metacercaria described in this study could not be conclusively categorized under any known South American species of Leucochloridium. In relation to the phylogenetic reconstructions, Leucochloridium sp. consistently clustered with L. perturbatum, and species delimitation analyses resulted in recognized Leucochloridium sp. from Argentina as a distinct species. The DNA sequences obtained in this study constitute the first genetic data generated for sporocyst broodsacs in South America. Future studies, incorporating morphology, genetic, and biological data, will be essential for both species identification and the elucidation of leucochloridiid diversity in the region.

A New Species of Cosmocerca Diesing, 1861 (Nematoda: Cosmocercidae) in Elachistocleis haroi Pereyra, Akmentins, Laufer, and Vaira, 2013 (Amphibia: Microhylidae) from South American Chaco.

PURPOSE: Cosmocercids are common nematodes that parasitize the digestive tract and lungs of amphibians and reptiles around the world. They are commonly found in leptodactylid and bufonid anurans in South America, primarily in Brazil and Argentina. This paper describes a new species of genus Cosmocerca based on specimens collected in a microhylid from the Dry Chaco ecoregion. METHODS: A total of 18 specimens of Elachistocleis haroi were collected in October 2011 in Chaco province and in December 2021 and March 2022 in Formosa province, Argentina, both areas of the Dry Chaco ecoregion. The morphology of the nematodes was studied in detail using light microscopy and scanning electron microscopy. RESULTS: One hundred and fifty-one nematodes were collected from the large intestines of E. haroi. Based on the morphology of the caudal papillae (rosette papillae and plectanes), the presence of two spicules and the absence of caudal alae in males, and the presence of two prodelphic ovaries in females, these specimens were allocated to the genus Cosmocerca. However, they presented unique characteristics that differentiate them from all known species. Cosmocerca wichiorum sp. nov. is similar to C. archeyi, C. australis, C. sardiniae, C. zugi, and C. leytensis by having four pairs of plectanes, but can be easily distinguished from all of them by the type, number, and arrangement of the precloacal (non-plectanes), adcloacal and postcloacal papillae, by the length of the spicules and by its different zoogeographical distribution. CONCLUSION: This is the 14th species of the genus Cosmocerca described in South America and the first one for the microhylid E. haroi from the Dry Chaco ecoregion.

First record of Cotylurus metacercariae (Trematoda:Strigeidae) in Biomphalaria straminea (Planorbidae) from Argentina: morphological and molecular identification.

In the study of the biology of trematode species, the knowledge of the larval stages in snail hosts is important to elucidate their complete life cycle. The goal of the present study was to describe a new tetracotyle-type metacercaria found in the freshwater mollusk Biomphalaria straminea sampled in a rice field from Corrientes province, Argentina. To this end, 1,768 snails were collected from the cultivated plots and irrigated channels during the flooding periods (from the time of sowing to soon after rice harvesting) between December 2016 and May 2017. We used morphological and molecular analysis to characterize the tetracotyle-type metacercariae. Its morphological traits and the internal transcribed spacers (ITS1 and ITS2 plus 5.8S; ~1200 pb) from nuclear ribosomal DNA (rDNA) were amplified and sequenced. From 1,768 specimens of B. straminea screened, 52 were found infected with metacercariae of tetracotyle type (2.9%) that were identified as Cotylurus genus. A total of 218 metacercariae were found encysted in the ovotestis or between the mantle and viscera of B. straminea. Bioinformatic analysis showed that the metacercarial rDNA sequences shared 94% identity with those of Cotylurus gallinulae from Mexico and 100% identity with those of Cotylurus sp. from Brazil. In this study, the morphological descriptions are supplemented with the first molecular identification of a metacercaria related to Cotylurus parasitizing planorbids from Argentina. Also, our study provides a new morphological description in B. straminea, thus broadening the geographical distribution. The life cycle of this Cotylurus metacercariae is unknown and there are no reports of adult stages parasitizing waterfowl in Argentina.

Morphological variation of Aplectana hylambatis (Nematoda: Cosmocercidae) from different anuran hosts and localities in Argentina.

Aplectana hylambatis is a nematode with a wide geographic distribution and low host specificity. In spite of numerous reports, until this moment, the morphological variations between different hosts and localities have not been studied. We studied 401 specimens collected from five host species from seven localities in Argentina, and examined the following morphological characters: mamelon-like cuticular protuberances anterior to the vulva, structure of the gubernaculum and the spicules, number and arrangement of caudal papillae, and the measurements of twelve characters in females and eleven characters in males. The results showed that mamelon-like protuberances and caudal papillae varied in number and arrangement between different hosts and localities. The metrical study revealed that five characters in males and six in females contributed to variability; nine characters showed significant differences between host species and localities. Specimens of A. hylambatis collected from R. arenarum formed a group clearly differentiated from the rest of the specimens. The results from this study highlight the importance of examining as many specimens as possible from different host samples and from several localities to cover the intraspecific variations.

Metacercariae of Strigeidae Parasitizing Amphibians of the Chaco Region in Argentina.

The goal of the present study was to analyze the metacercariae found in adult amphibians collected in the Argentinean Chaco region. A total of 194 frogs, Leptodactylus chaquensis, Leptodactylus latinasus, and Lepidobatrachus laevis was examined for digeneans. Three different larval trematodes of the genus Strigea (Digenea, Strigeidae) were found infecting the liver, mesentery, body cavity, and muscle of frogs. These metacercariae are described and illustrated for the first time and provide new information on the composition of metacercariae in amphibians, thus contributing to the knowledge of larval trematodes biodiversity in the Neotropical region. We also present new information on the morphology and morphometry of strigeid metacercariae.

Larval digenean communities in Biomphalaria species in two contrasting wetlands from South America.

A key factor in the colonization probabilities of parasites is the host's characteristic habitat. Considering that rice fields are simple habitats compared with natural wetlands, we comparatively analyzed the composition of the cercariae communities in Biomphalaria snails in an agricultural and a nonagricultural habitat of Corrientes Province, Argentina. We collected 2998 Biomphalaria snails from November 2011 to May 2012: B. tenagophila, B. occidentalis, B. peregrina, and B. orbignyi in the nonagricultural habitat and B. straminea in the agricultural habitat. Nine cercaria species were found in the nonagricultural habitat and 12 in the agricultural habitat, with overall parasite prevalence of 9.27 and 7.69%, respectively. The overall prevalence and mean species richness of cercariae showed no significant differences between habitats. The cercariae communities of the 2 habitats showed low similarity (38%), sharing 4 species. The mean species diversity of cercariae was higher in the nonagricultural habitat. Our results suggest that rice fields provide conditions for the hosts and cercariae that are somewhat similar to those of nonagricultural wetlands, although the contrasting characteristics of habitats can influence the presence of different intermediate and definitive hosts and consequently impact parasite diversity.

First report of Schulzia travassosi (Nematoda, Trichostrongylina, Molineoidea) for amphibians of the Chaco region in Argentina and proposal of Oswaldocruzia melanostictusi nov. comb.

This is the first record of the nematode parasite Schulzia travassosi (Trichostrongylina, Molineidae) in two Argentinean amphibians, Leptodactylus bufonius and Rhinella major, collected in two localities of the Chaco region, Las Lomitas (Formosa Province) and Taco Pozo (Chaco Province). The species was observed using light and scanning electron microscopy (SEM) and compared with previous studies of Paraguayan specimens. Regarding metric characters, the measurements found in Argentinean specimens generally did not differ from those of Paraguayan specimens; some differences were observed in the total length of males and females (some longer and some shorter than Paraguayan specimens), length of the oesophagus (in almost all specimens shorter than in Paraguayan ones) and position of the vulva (nearer to posterior end in Argentinean specimens). The branches and sphincter of ovejector are slightly longer than in Paraguayan female specimens. In males, ray 4 is almost the same length as rays 2, 3 and 5, 6. Cephalic end, cephalic vesicle, synlophe and vulvar depression were viewed under SEM. Schulzia melanostictusi Chopra, Shing and Kumar, 1986 is reassigned as Oswaldocruzia melanostictusi (Chopra, Shing and Kumar, 1986) nov. comb.

Helminth community structure in the Argentinean bufonid Melanophryniscus klappenbachi: importance of habitat use and season.

The goal of this study was to evaluate the relative influence of terrestrial habits, season, and host body size on the species richness and abundance of helminth parasites in the toad Melanophryniscus klappenbachi, for which a greater abundance of nematode parasites was expected. A total of 90 toads were collected in the Chaco Province, Argentina. The helminth community found in infected toads included 17 taxa and was dominated particularly by larval parasites. Contrary to our expectations, nematode species showed lower values of infection parameters. Infected toads harbored a maximum of seven species, and the mean helminth richness was 3.16 ± 1.66 species per infected toads. Season played a significant effect on determining the species richness and abundance of the parasite infracommunity. Similarly, the prevalence of infection of several helminth species (8/47%) varied greatly over time. Host body size was the main factor in determining the infrapopulation structure of helminth parasites. Species richness was significantly and negatively correlated with host body size. Strong associations were observed mainly between larvae of some species. The transmission strategies of parasites suggest that this bufonid acquires infections through direct contact with larval parasites from aquatic and terrestrial habitats and by ingestion of infective larvae. The characteristic of the host tegument, such as the presence of alkaloids, could significantly contribute to the low occurrence of infection by skin-penetrating nematodes. Results also showed that diets and mobility of the host and the local microhabitat conditions play an important role in parasitic infections of toads.

Coexistence of helminth species in Lysapsus limellus (Anura: Pseudidae) from an Argentinean subtropical area: influence of biotic and abiotic factors.

The need for studies on helminth communities of South American amphibians was addressed by examining changes in composition and population dynamics of the helminth component and infracommunities in the frog Lysapsus limellus Cope, 1862, from 1994 to 1996. Two pond types were considered, one permanent and one semipermanent. The main goals of this study were (1) to investigate the relationships between pond type, season, study time, frog body size, and frog sex and the presence-absence and counts of helminth parasite species in the frog host, L. limellus, and (2) to examine the co-occurrence of the different parasite species in the frog host in terms of the structure, assembly, and dynamics of the helminth infracommunity. Parasite presence and absence were analyzed using logistic regression and parasite counts were analyzed using log-linear modeling. To examine the association between parasite species, a principal components analysis was carried out on the correlation matrix for the counts. The pattern of co-occurrences was also examined through a randomization test. The main results were as follows: (1) five parasite species were found in the infracommunity; (2) the pond type and the host size class were the principal factors related to the presence and absence of parasites for the three dominant species, while the year of study and the host sex were only important for one of the species; (3) for the parasite counts, many more factors were significant, with body size class and pond type always important factors for the three core species of the infracommunity, with season, year of study, and sex also sometimes important, and (4) strong associations were observed between some helminth species of the host from the permanent pond, but the same species did not co-occur in frogs in the semipermanent pond. The life histories of the five species can be considered as opportunistic or "r strategists."