Sybelle Bellay

A host-endoparasite network of Neotropical marine fish: are there organizational patterns?

Properties of ecological networks facilitate the understanding of interaction patterns in host-parasite systems as well as the importance of each species in the interaction structure of a community. The present study evaluates the network structure, functional role of all species and patterns of parasite co-occurrence in a host-parasite network to determine the organization level of a host-parasite system consisting of 170 taxa of gastrointestinal metazoans of 39 marine fish species on the coast of Brazil. The network proved to be nested and modular, with a low degree of connectance. Host-parasite interactions were influenced by host phylogeny. Randomness in parasite co-occurrence was observed in most modules and component communities, although species segregation patterns were also observed. The low degree of connectance in the network may be the cause of properties such as nestedness and modularity, which indicate the presence of a high number of peripheral species. Segregation patterns among parasite species in modules underscore the role of host specificity. Knowledge of ecological networks allows detection of keystone species for the maintenance of biodiversity and the conduction of further studies on the stability of networks in relation to frequent environmental changes.

Ectoparasites and endoparasites of fish form networks with different structures

Hosts and parasites interact with each other in a variety of ways, and this diversity of interactions is reflected in the networks they form. To test for differences in interaction patterns of ecto- and endoparasites we analysed subnetworks formed by each kind of parasites and their host fish species in fish-parasite networks for 22 localities. We assessed the proportion of parasite species per host species, the relationship between parasite fauna composition and host taxonomy, connectance, nestedness and modularity of each subnetwork (n = 44). Furthermore, we evaluated the similarity in host species composition among modules in ecto- and endoparasite subnetworks. We found several differences between subnetworks of fish ecto- and endoparasites. The association with a higher number of host species observed among endoparasites resulted in higher connectance and nestedness, and lower values of modularity in their subnetworks than in those of ectoparasites. Taxonomically related host species tended to share ecto- or endoparasites with the same interaction intensity, but the species composition of hosts tended to differ between modules formed by ecto- and endoparasites. Our results suggest that different evolutionary and ecological processes are responsible for organizing the networks formed by ecto- and endoparasites and fish.

Two new species of Sciadicleithrum [Monogenea, Dactylogyridae] parasites of Neotropical cichlid fishes from the Parana River, Brazil

Two new species of Sciadicleithrum are described from the gills of Neotropical cichlid fishes collected from Paraná River, Brazil. Sciadicleithrum satanopercae sp. nov. is described from the gills of Satanoperca pappaterra and differs from congeners by having a dorsal anchor with the distal portion complex and the inner margin with a “denticulum” between shaft and point. Sciadicleithrum joanae sp. nov. is described from the gills of Crenicichla niederleinii and C. britskii collected from Paraná River. Sciadicleithrum joanae sp. nov. differs from congeners by having a male copulatory organ comprising about half a clockwise loop and a vaginal pore “bulb-shaped”.

A new species of Demidospermus Suriano, 1983 (Monogenea, Dactylogyridae) parasitic on Loricariichthys platymetopon Isbrücker et Nijssen (Loricariidae, Siluriformes) from the Upper Paraná River floodplain, Brazil

Demidospermus paranaensis sp. nov. is described from the gills of Loricariichthys platymetopon Isbrücker et Nijssen (Loricariidae, Siluriformes) from the Upper Paraná River floodplain, Brazil. This new species differs from other members of Demidospermus in the following features: tegument with annulations throughout trunk and peduncle, eyes absent, longer male copulatory organ (MCO) with ovate base. Demidospermus paranaensis sp. nov. is similar to its congenerics by having tandem gonads, a counterclockwise-coiled MCO, non-articulated groove-like accessory piece serving as a MCO guide, sinistral vaginal aperture, and V-shaped haptoral bars.

Influence of host diet and phylogeny on parasite sharing by fish in a diverse tropical floodplain.

The patterns of parasite sharing among hosts have important implications for ecosystem structure and functioning, and are influenced by several ecological and evolutionary factors associated with both hosts and parasites. Here we evaluated the influence of fish diet and phylogenetic relatedness on the pattern of infection by parasites with contrasting life history strategies in a freshwater ecosystem of key ecological importance in South America. The studied network of interactions included 52 fish species, which consumed 58 food types and were infected with 303 parasite taxa. Our results show that both diet and evolutionary history of hosts significantly explained parasite sharing; phylogenetically close fish species and/or species sharing food types tend to share more parasites. However, the effect of diet was observed only for endoparasites in contrast to ectoparasites. These results are consistent with the different life history strategies and selective pressures imposed on these groups: endoparasites are in general acquired via ingestion by their intermediate hosts, whereas ectoparasites actively seek and attach to the gills, body surface or nostrils of its sole host, thus not depending directly on its feeding habits.

Is the community of fish gill parasites structured in a Neotropical floodplain

Sixty-one specimens of the piranha Serrasalmus marginatus Valenciennes, 1837 were analyzed, aiming at assessing the community structure of their gill parasites. The samples were collected in lagoons of the Paraná, Ivinheima and Baia Subsystems within the Upper Paraná River Floodplain (Brazil). Host size and sex had little or no influence on the abundance and prevalence of parasites. The organization of the gill parasite infracommunities of S. marginatus was significantly non-random according to null models and ordination analyses. In general, parasite infrapopulations were not affected by interspecific associations or host characteristics (e.g. size, sex), what highlights the importance of local habitat characteristics to community organization of gill parasites of S. marginatus in the Upper Paraná River Floodplain.

Parasitism by larval tapeworms genus Spirometra in South American amphibians and reptiles: new records from Brazil and Uruguay, and a review of current knowledge in the region.

Spargana are plerocercoid larvae of cestode tapeworms of the genus Spirometra, Family Diphyllobothriidae, parasitic to frogs, reptiles, birds and mammals. This parasitic disease in humans can be transmitted through the use and consumption of amphibians and reptiles. The available knowledge about Spirometra in South America is scarce, and there are only a few reports on the occurrence of sparganum in amphibians and reptiles, many of them published in old papers not easily available to researchers. In this work we present a review on this topic, provide new records in two species of amphibians and 7 species of reptiles from Brazil and Uruguay respectively. We also summarize current knowledge of Spirometra in the continent, along with an updated of host taxonomy. We could gather from the literature a total of 15 studies about amphibian and reptile hosts, published between 1850 and 2016, corresponding to 43 case reports, mostly from Brazil (29) and Uruguay (8), Argentina (3), Peru (2), and Venezuela (1); the majority of them related to reptiles (five lizards and 26 snake species), and 14 corresponded to amphibians (9 anurans). Plerocercoid larvae were located in different organs of the hosts, such as subcutaneous tissue, coelomic cavity, peritoneum, and musculature. The importance of amphibians and reptiles in the transmission of the disease to humans in South America is discussed. Relevant issues to be studied in the near future are the taxonomic characterization of Spirometra in the region and the biological risk of reptile meat for aboriginal and other rural communities.

Host-Parasite Networks: An Integrative Overview with Tropical Examples

The lack of ecological studies on parasite species is contradictory with their high diversity. In this context, the ecological network approach has drawn attention to patterns of tropical host-parasite interactions; however, it is still very restricted to a few taxonomic groups. In tropical regions, studies on host-parasite networks have encompassed specially fish, amphibian hosts, and malaria parasite communities of birds. High specificity is peculiar to parasites, either considering the host species or the site of infection. Variations in specificity indicate differentiated structural patterns between ecto- and endoparasites networks, as well as larval and adult stages of parasites, influencing the values of connectivity, nestedness, and modularity. Host characteristics also influence the structure of networks, including phylogenetic relationships and diet. Similarly to free-living species in ecosystems suffering the influences of environmental change, parasite species may also be extinct due to primary extinctions of hosts or possibly present new patterns of interaction due to the arrival of invasive species in the environment. New studies should explore network patterns between tropic and non-tropic environments, in addition to the use of molecular tools to identify especially cryptic parasites, which may provide better-supported results.