Population genetic analysis informs dispersal capacity in representative marine trematodes from Family Microscaphidiidae and Family Paramphistomatidae

In marine and terrestrial systems, life history drives the distribution of organisms and informs the spatial scale of population connectivity. Nearly all bony reef fishes and invertebrates have a bipartite life cycle with a planktonic larval stage, which increases the organism’s dispersal capacity, and concludes with a relatively non-dispersive adult phase. While many studies have identified the relevant spatial scale for studying population structure in fishes and invertebrates, few have done the same for parasitic taxa, which have even more complex life histories with a higher diversity in the range of dispersal strategies they use. Parasite taxa differ in (1) life cycle complexity, (2) host specificity, and (3) the types of hosts they can infect. All variables are likely to have both independent and synergistic effects on dispersal capacity. This study estimated the dispersal of two complex life cycle parasites - marine trematodes from Family Microscaphidiidae and Family Paramphistomatidae - across two separate but similar island systems. Trematodes were collected from reef fish sampled from the islands of the Northern Line Islands and French Polynesia. After sequencing a 743 bp region of the mtDNA cytochrome oxidase 1 (CO1) locus, I examined the population structure of 83 adult microscaphidiids across the Northern Line Islands and found significant, high genetic structure, suggesting low gene flow. I also examined the population structure of 132 adult and larval paramphistomes across islands in French Polynesia, and found evidence of two cryptic species, who also likely had low gene flow across the islands. Lastly, I estimated a dispersal kernel of 8 – 90 meters for the paramphistomes that had significant isolation by distance. Overall, this study provides empirical evidence for host-driven parasite dispersal in marine trematodes collected from two island systems in the Pacific Ocean, which directly contributes to the current lack of breadth and depth of parasite research.