Conference Agenda

Polychaetes constitute a significant portion of the biodiversity and abundance in marine sediments, playing essential roles as prey and predators to other free-living species and as hosts for various parasites. Over a two-year period in coastal British Columbia, Canada, we screened diverse groups of polychaetes for parasites and hyperparasites. As a result, we discovered more than 40 novel species of parasitic alveolates (including ciliates, dinoflagellates, and apicomplexans) and animals (e.g. orthonectids). Among these parasites, gregarine apicomplexans are particularly interesting since they are highly diverse and abundant and can harbour their own parasites (i.e., hyperparasites), namely metchnikovellids. We observed the morphology of these novel parasites and hyperparasites using light and electron microscopy. Also, we inferred single-gene phylogenetic trees based on small subunit ribosomal RNA sequences for larger taxonomic coverage and multigene phylogenetic trees using transcriptomic and genomic data for better resolution. By synthesizing results from morphological and molecular analyses, we explore phylogenetic diversity and relationships, patterns of coinfection and host specificity, and evidence for codiversification between hosts and parasites.

Animal microbiomes have been recognized to have significant impact on animal behaviour, development, and health. For parasites, the source of their microbes is likely acquired from their hosts, making host identity a potential factor to explain the variation of microbiome composition among conspecific parasites. To test this, we compared the microbiomes of trematode Maritrema poulini metacercariae (encyst larval form) across three different host hierarchical levels: parasites within the same host individual; parasites from different conspecific host individuals; and parasites from amphipod Paracalliope fluviatilis versus isopod Austridotea annectens hosts. We found there was no difference in alpha diversity for the microbiome of M. poulini metacercariae across all three different host hierarchical levels. However, there were differences in beta diversity for the parasites’ microbiomes under two hierarchy levels: (i) for parasites from amphipod vs isopod hosts; (ii) for parasites from different individual isopod hosts. Differential abundance analysis also showed differences of some bacteria at phylum level. To conclude, the study shows that host identity, such as host species or conspecific host individuals, impacts parasite microbiome composition, but has no influence on taxonomic diversity and richness within parasite microbiomes.

Cardicola forsteri and C. orientalis are economically significant aporocotylids infecting the circulatory system of ranched Southern bluefin tuna (SBT), Thunnus maccoyii, in South Australia. SBT are typically ranched for 3-6 months and without praziquantel treatment Cardicola spp. can cause substantial losses to the SBT industry. The aim of this study was to determine the Cardicola spp. infection dynamics during an extended period of SBT ranching. SBT gills and hearts were collected at 12 time points (10 to 40 weeks post praziquantel treatment) from fish farmed by a single company for a twelve-month period. Cardicola spp. infection was quantified by adult fluke counts in the heart of SBT and quantitative polymerase chain reaction (qPCR) to detect C. forsteri and C. orientalis ITS-2 DNA in the gills. C. forsteri adult prevalence and intensity peaked 25 weeks post treatment (PT) before the infection intensity significantly decreased for the remainder of the study. At 17 weeks PT C. forsteri prevalence reached and stayed at 100%. Ranching outside of the usual timeline will allow the SBT industry to provide a fresh product for a longer period and understanding the infections risks will help farmers make informed health management decisions.