Dicyemid fauna composition and infection patterns in relation to cephalopod host biology and ecology.

Ten Southern Hemisphere cephalopod species from six families collected from six localities in western, southern and eastern Australia were examined for dicyemid parasites. A total of 11 dicyemid species were recorded, with three cephalopod species uninfected, four infected by one dicyemid species and three infected by multiple dicyemid species. Dicyemid species prevalence ranged from 24-100%, with observed infection patterns explored due to host size, host life history properties, host geographical collection locality and inter-parasite species competition for attachment sites, space and nutrients. Left and right renal appendages were treated as separate entities and four different patterns of infection by asexual and sexual dicyemid stages were observed. The detection within a single host individual of asexual dicyemid stages in one renal appendage and sexual dicyemid stages in the other renal appendage supported the notion that developmental cues mediating stage transition are parasite-controlled, and also occurs independently and in isolation within each renal appendage. Our study exploring dicyemid parasite fauna composition in relation to cephalopod host biology and ecology therefore represents a thorough, broad-scale taxonomic analysis that allows for a greater understanding of dicyemid infection patterns.