Do symbiotic polychaetes migrate from host to host

Abstract

Britayev, T.A. and Mekhova, E.S. 2014. Do symbiotic polychaetes migrate from host to host? Memoirs of Museum Victoria 71: 21–25. It is generally considered that symbiotic animals colonise their hosts during their early stages of development. The main goal of the present study was to assess whether post-settled stages (juvenile and adult) of the symbiotic polychaete Paradyte crinoidicola are able to colonise their host comatulid crinoids. We also considered possible motives for symbiont migrations based on the intraspecific traumatism, size and sex structure data, and distribution pattern of P. crinoidicola. To this end, field sampling and experiments with depopulated hosts of the comatulid crinoid Himerometra robustipinna were carried out. The infestation prevalence was 62%, each infested host harbored from 1 to 7 polychaetes, and multiple infestations with 2 or 3 polychaetes per host were common. Mean intensity was 2.1 specimens per host. The dispersion coefficient was 1.7, greater than 1, indicating the tendency to contagious distribution pattern. Male/female ratio in P. crinoidicola was very close to the expected 1:1 ratio. About 33 % of P. crinoidicola had a traumatised posterior ends, and 31% damaged and regenerated parapodia, elytra and cirri, likely attributable to intra-specific fighting. In the field experiments depopulated crinoids were rapidly colonised by symbionts. The infestation characteristics of recolonised hosts didn’t differ significantly to that of the control. Mean length of polychaetes and the ratio of small polychaetes to large polychaetes were similar in the experimental series and in the control, indicating a colonisation of crinoids not only by settling larvae, but predominately by migrating post-settled juveniles and adults. The male/female ratio deviated significantly in favor of males in the experimental series, suggesting that males more than females actively migrate among hosts. Intraspecific competition and searching for mating partners are proposed as causes for host swapping in P. crinoidicola.