Abstract
Specialized interactions tend to be more common in systems that require strong reciprocal adaptation between species, such as those observed between parasites and hosts. Parasites exhibit a high diversity of species and life history strategies, presenting host specificity which increases the complexity of these antagonistic systems. However, most studies are limited to the description of interactions between a few parasite and host species, which restricts our understanding of these systems as a whole. We investigated the effect of the developmental stage of the parasite on the structure of 30 metazoan fish-parasite networks, with an emphasis on the specificity of the interactions, connectance and modularity. We assessed the functional role of each species in modular networks and its interactions within and among the modules according to the developmental stage (larval and adult) and taxonomic group of the parasites. We observed that most parasite and host species perform a few interactions but that parasites at the larval stage tended to be generalists, increasing the network connectivity within and among modules. The parasite groups did not differ among each other in the number of interactions within and among the modules when considering only species at the larval stage. However, the same groups of adult individuals differed from each other in their interaction patterns, which were related to variations in the degree of host specificity at this stage. Our results show that the interaction pattern of fishes with parasites, such as acanthocephalans, cestodes, digeneans and nematodes, is more closely associated with their developmental stage than their phylogenetic history. This finding corroborates the hypothesis that the life history of parasites results in adaptations that cross phylogenetic boundaries.
Highlights
The application of network theory to the study of ecological interactions has significantly improved our understanding of the mechanisms generating community structure [1,2,3]
The general structure of the networks analyzed revealed a tendency of a few hosts to have a high susceptibility to parasitism (Fig. 1A); a low number of parasites was found in several hosts (Fig. 1B)
As expected due to the low host susceptibility and high parasite specificity, the values of connectance (%) observed in the networks were relatively low. This parameter was negatively correlated with the total number of species (r = 20.87; p,0.001; Fig. 2A) and positively correlated with the proportion of parasite species at the larval stage in the networks (r = 0.46, p = 0.01; Fig. 2B)
Summary
The application of network theory to the study of ecological interactions has significantly improved our understanding of the mechanisms generating community structure [1,2,3]. Despite some recent advances in the elucidation of host-parasite networks, most studies have focused on the description of a few parasite and host species of ecological or commercial interest, which has resulted in the limited understanding of these systems as a whole. Host-parasite systems are very complex and include parasites with distinct life history strategies. Some fish parasites require intermediate hosts (i.e., parasites with a complex life cycle), whereas others need only a single host (i.e., parasites with a simple life cycle) [9,10]. Some fish may be parasitized by both larval and adult stages and be exposed to a wide variety of parasite species [9,10]
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