Genetic analysis of dicyemid infrapopulations suggests sexual reproduction and host colonization by multiple individuals is common

Dicyemida is a group of small-bodied marine parasites infecting cephalopods with many unknown life history details, such as their population structure and diversity, and their relation to sexual and asexual reproductive stages. To reveal (infra)population structure of Dicyema moschatum Whitman, 1883 in its host ( Eledone moschata Lamarck, 1798 ), we isolated microsatellite sequences from a draft genome of D. moschatum and tested the loci for amplification success and genetic diversity. Eight microsatellite loci were selected for an analysis of D. moschatum populations from several octopus individuals sampled at two Mediterranean localities. The majority of microsatellite alleles were shared across the studied range, but several private alleles were also identified. Analysis of population structure identified two to four genetic clusters, mostly concordant with the geographic origin of the samples. Allelic patterns seen in individual dicyemid genotypes revealed that although dicyemids inside one host individual show low genetic variance, they do not represent genetically identical clones. These results suggest that infection is established by several dicyemid larvae within the lifetime of the host and sexual reproduction of dicyemids occurs inside the host.