Dr. George-Nascimento-Failla, Mario

The coasts of central Chile and central California are important points of comparison in the study of ecological convergence such as a host’s parasite load because of their similar environmental conditions and the shared presence of many families of different species. In this study, the diversity of parasites in fish species from both zones was analyzed and compared to establish if there are similarities between them. The presence of 6 taxonomic groups of parasites was determined using published literature and databases for each location. A presence-absence matrix was created for the fish species studied in Chile and California, and a similarity analysis was carried out to prove whether the parasite loads of both zones were similar. The parasite taxa most frequently found in fish in central California were Digenea and Nematoda, whereas in central Chile the common taxa were Digenea, Annelida, Copepoda, Acanthocephala, and Nematoda. The similarity analysis showed that the parasite composition was different between zones. Nevertheless, overlaps were obtained in the parasitic diversity grouping the host in 3 host groups, one of which consists of hosts from both zones. This difference can be explained by the low parasitic diversity in the assemble of rocky intertidal fishes in California, potentially due to the limited amount of existing studies on intertidal fish parasites in California, along with other possible factors not explored in the present study.

Biological interactions and environmental constraints alter life-history traits, modifying organismal performances. Trematode parasites often impact their hosts by inducing parasitic castration, frequently correlated with increased body size in the host (i.e., gigantism hypothesis), which is postulated to reflect the re-allocation of energy released by the reduction in the reproductive process. In this study, we compared the effect of a trematode species on shell size and morphology in adult individuals of the intertidal mussels Perumytilus purpuratus (>20 mm) collected from two local populations of contrasting environmental regimes experienced in central-southern Chile. Our field data indicates that in both study locations, parasitized mussels evidenced higher body sizes (shell length, total weight and volume) as compared with non-parasitized. In addition, parasitized mussels from the southern location evidenced thinner shells than non-parasitized ones and those collected from central Chile, suggesting geographical variation in shell carbonate precipitation across intertidal habitats of the Chilean coast. In laboratory conditions, mussels collected from a local population in central Chile were exposed to two temperature treatments (12 and 18 °C). Parasitized mussels showed higher growth rates than non-parasitized, regardless of the seawater temperature treatments. However, the metabolic rate was not influenced by the parasite condition or the temperature treatments. Our field and laboratory results support the parasite-induced gigantism hypothesis, and suggest that both the thermal environment and geographic location explain only a portion of the increased body size, while the parasitic condition is the most plausible factor modulating the outcome of this host-parasite interaction.