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PARASITOFAUNA OF "PIRARUCU" (Arapaima gigas, Pisces) IN NATURAL AND NONNATURAL AREA: TESTING THE ENEMY RELEASE HYPOTHESIS AND THE PATTERNS OF PARASITE-HOST INTERACTIONS

Grant number: 22/05857-6
Support Opportunities:Scholarships in Brazil - Post-Doctoral
Effective date (Start): January 01, 2023
Effective date (End): August 31, 2025
Field of knowledge:Biological Sciences - Zoology - Applied Zoology
Principal Investigator:Lilian Casatti
Grantee:Lidiane Franceschini
Host Institution: Instituto de Biociências, Letras e Ciências Exatas (IBILCE). Universidade Estadual Paulista (UNESP). Campus de São José do Rio Preto. São José do Rio Preto , SP, Brazil

Abstract

Introduction of species outside their native range can lead to biological invasion processes, which can alter ecological relationships in new distribution areas, including host-parasite interactions. On the other hand, parasitism can influence the invasion process, helping or limiting the expansion of their hosts. In this scenario, bipartite networks are considered effective tools for studying parasite-host interactions, assisting to predict impacts caused by biological invasions. In the upper Paraná River basin there are ~74 species of non-native fishes, with the record of the "pirarucu" Arapaima gigas being one of the most recent. Considering that knowledge about the effects of A. gigas invasion in the receiving basin is still incipient, information about its biology (e.g., parasitism and diet) and factors that may influence the success of its establishment in the new area are essential to support local management of this species. In this study, we intend to evaluate the parasitic community of A. gigas in an area of non-natural distribution (Rio Grande, upper Paraná River basin, State of São Paulo) and in its natural occurrence area (based on the determination of the origin of the invasive propagules). For that, the following hypotheses should be tested: 1) considering the Enemy Release Hypothesis, we expect that the parasitic fauna of A. gigas will present greater species richness and taxonomic diversity in its natural distribution area in relation to the non-natural area; 2) the ecological descriptors of parasitism (prevalence [P], mean intensity of infection/infestation [MII] and mean abundance [MA]) of A. gigas will show differences between natural and non-natural distribution areas; 3) based on the analysis of bipartite networks, we expect that the structures of the host-parasite networks will present differences between the natural and non-natural distribution areas, considering the origin of the parasite (native or non-native) and transmission strategy; 4) the diet of A. gigas will present differences in its composition between the sampling areas, due to the supply of different food items and structure of habitats, and consequently, the fauna of trophically transmitted parasites will be different between areas as a function of the ingestion of different food items that act as potential hosts. A minimum of 60 specimens of A. gigas will be analyzed (30 from each sampling area) obtained from fishermen. The hosts will be euthanized and taken to the laboratory, where the sex will be determined and the standard length (cm) and total mass (g) will be measured. Afterwards, they will have their skin (mucus), fins and internal organs inspected for the presence of parasites. The stomachs will be fixed for analysis, identification and determination of the mass of food items (gravimetric method), and subsequent comparison of the diet composition of A. gigas between the sampling areas. After the taxonomic identification of the parasites, the component community of the parasites (richness and diversity), parasitological attributes (P, MII and MA) and the effect of diet on the composition of parasites trophically transmitted will be characterized and compared between the sampling areas. Weighted bipartite networks will be used to evaluate differences in the patterns of interaction between specimens of A. gigas and their respective parasites in areas of natural and non-natural distribution, using connectance, weighted nestedness and modularity as quantitative descriptors. To determine the importance of each parasite taxon for the structure of the host-parasite interaction networks, the betweenness centrality index (BC) will be estimated. Thus, we hope to provide data on how A. gigas is interfering with ecological relationships in the new area, including host-parasite interactions, evaluating possible co-introductions/co-invasions of parasites and other pathogens, and possible changes in food webs in the receiving basin.

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