Enfatizando a ecologia nas interações parasito-hospedeiro.

Abstract

Parasites require at least one host to survive and cause some damage to it. Host-parasite interactions occur in many different ways, which makes this difficult relationship to be modeled or approached from the point of view of ecological general theories and hypotheses. Top-down and bottom-up mechanisms for example are widely used to describe trophic effects in community ecology. The parasite-host interactions are configured much like the predator-prey relationships in which parasites act as predators and appropriate host resources, which act as prey. In this thesis the host-parasite interaction is addressed from the top-down/bottom-up perspective in order to consider the relationship between weight and body length (body condition) as a parameter to evaluate the host welfare, and correlate such measure with the biomass of parasites. This new approach predicts that interactions can be mediated by resources for the parasite or by the immunity of the host. To illustrate such approach, a case study investigates the correlation between abundance of endoparasites and the relative condition factor of 15 species of fish of different trophic guilds sampled over 13 years in the Upper Parana River floodplain. The positive correlation observed for all guilds can be attributed to both external factors such as high food availability for the hosts, which in turn provide quality resources for the parasites, as to whether hosts with better body condition have a higher tolerance parasitism. Under other ecological perspective, the Enemy Escape Hypothesis justifies the potential success in the introduction of species process the loss of their natural predators and parasites. Thus, another objective of this study was to compare the parasitic fauna of the gills of Plagioscion squamosissimus in rivers where it is native and rivers where it is introduced from the point of view of this hypothesis. To this end, host of specimens of each river were analyzed and the total wealth of parasites in native basins was significantly higher than in basins introduced, suggesting that during the introduction process the fish species lost most of their gill parasites. The fact that the parasites do not necessarily colonize successfully new areas has shown one more factor contributing to the success of the establishment of non-native fish species into new regions.