Dr. George-Nascimento-Failla, Mario

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.

Studies on helminth communities associated with didelphids are scarce; the majority of works have focused at taxonomic level. To increase the ecological knowledge of these host–parasite associations, during March (dry season) of 3 consecutive years (2013–2015) a total of 49 adults of the gray four-eyed opossum (Philander opossum) was collected in the Neotropical portion of Mexico (Agua Fría, Chiapas State) and examined for helminths. The main objectives of this study were to describe the infra- and component communities of helminths associated with P. opossum and to compare the helminth fauna of the Mexican population of this host species with those studied in French Guiana and in other Mexican terrestrial didelphids. The helminthological record of this host consisted of 12 species: 7 taxa of Nematoda, 3 of Trematoda, 1 Cestoda, and 1 Acanthocephala. Eight of the 12 taxa have been previously recorded in Didelphidae and 4 represent accidental infections (Glossocercus sp., Stomylotrema vicarium, Spirura mexicana and Acanthocephala gen. sp.). Diet of hosts is the main structuring factor of the communities (92% of the helminth species were recruited through ingestion). Forty-eight hosts were parasitized by at least 1 helminth species; Rhopalias coronatus was the most prevalent and abundant species in the hosts sampled. No significant differences were found in global prevalence among the helminth species present in all samplings, considering host sex and year. The dominance exerted by R. coronatus led to low values of evenness and diversity at both community levels. No significant differences were observed in composition of helminth species among the 3 sampling years regarding sex. The results of our study showed changes in helminth abundance at infracommunity level; during the first sampling these changes are explained by species with direct life cycle (Viannaia sp. and Cruzia tentaculata), whereas in last 2 surveys the explanation can be attributed to species with heteroxenous life cycles (particularly R. coronatus, Duboisiella proloba, and Turgida turgida). Thirty-three percent of the helminth species recorded in P. opossum in Agua Fría is shared with the other 2 terrestrial species of didelphids sampled in different sites of Mexico: Didelphis marsupialis and Didelphis virginiana. In contrast, samples from French Guiana and Agua Fría, differ in terms of helminth fauna, confirming that the helminth communities of opossum species inhabiting the same locality show higher levels of taxonomic similarity than communities of conspecific marsupials allopatrically distributed.

Notothen fishes (Nototheniidae) have been recorded on the coasts of South America, from 35°S to southern. Little is known about the biology of intertidal notothen fishes or their relationships with other species, including parasites. Here, we analyzed the parasitic fauna of a species of Notothenia collected from the rocky intertidal of Lebu, south-central Chile (36°S) and compared the parasite community of this host with other 9 fish species commonly found in rocky intertidal pools. Among the tested species, Notothenia sp. had the highest parasite richness (21 parasitic taxa vs. 1 to 9 parasitic taxa). The composition of parasite species was different among fishes, with similarity indices between 0 and 33%. The parasite composition of Notothenia sp. was most similar to Calliclinus geniguttatus (27%). The most abundant and prevalent parasites found in Notothenia sp. were the copepod Caligus cf. cheilodactyli, Tetraphyllidea larvae, anisakid nematodes, and several acanthocephalan species, which are typical of other fish from the subtidal and bento-demersal zones. Therefore, we conclude that the juveniles of Notothenia sp. were a few months old and had their parasites when reaching the intertidal zone, acquired some generalist parasites during their stay in this habitat, such as Holobomolochus chilensis and Lecithaster macrocotyle. Most notothen fishes are from Antarctic and Sub-Antarctic waters, therefore, it is possible that this fish came from another habitat but also from the austral region of South America. Notothenia sp. could not be specifically identified because of different results between morphological and genetic analyses.

The most studied digenean of marine organisms in Chile is by far Proctoeces humboldti, a parasite of the intestine of the clingfish Sicyases sanguineus and gonad of the keyhole limpet Fissurella spp. (progenetic metacercariae). The mussel Perumytilus purpuratus has been suggested as the first intermediate host for this digenean. In a study examining the parasites of S. sanguineus from central Chile, we found specimens of Proctoeces showing significant morphological differences with P. humboldti. To assist in the resolution of the taxonomic identification of these specimens, as well sporocysts obtained from the mussel P. purpuratus from central and northern Chile, phylogenetic studies using DNA sequences from the SSU rRNA, as well the LSU rRNA and Cox 1 gene were performed. Results showed that the clingfish S. sanguineus is a host for two species of Proctoeces (P. humboldti and P. syciases n. sp.) along the northern and central Chilean coast, without geographic separation; the mussel P. purpuratus is the first intermediate host for P. syciases n. sp. but not for P. humboldti in central and northern Chile. Fissurellids (Archaeogastropoda) along the Chilean coast harbor only progenetic stages of P. humboldti, but there is no evidence of progenesis for P. syciases. The reinstatement of Proctoeces humboldti is strongly suggested.