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.

Galaxias maculatus is an abundant freshwater fish species in Chilean continental waters where it plays important ecological functions, yet few parasitological records of this species exist in Chile and all of them cover a very limited geographic range. The objective of this study was to assess large scale geographic variation in composition of parasite infracommunities of Galaxias maculatus. Specifically, parasite infracommunities of this species were compared among 11 locations across 9 degrees of latitude and 3 ecosystem types (lake, river and estuary). Most taxa found had been previously reported in Chile and Argentina. However, this is the first report for Tylodelphys sp. in this host in Chile. Furthermore, the cranial parasite Tylodelphys sp. had the highest overall prevalence and abundance compared to other parasite species. Despite the fact that the abundance of Tylodelphys sp. was not significantly correlated with Fulton’s condition factor of fish, infected fish seem to have a better body condition compared to uninfected ones. The most important source of variation in composition of infracommunities was the sampling location. Furthermore, fish from lakes have a different composition of parasite infracommunities mainly due to higher abundances of Tylodelphys sp.

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.