Deleterious effects of the ciliate epibiont Zoothamnium sp. on fitness of the copepod Acartia tonsa

Abstract

The effects of the colonial peritrich ciliate epibiont, Zoothamnium sp., on fitness components of the copepod Acartia tonsa were examined during a three-week infestation event in Long Island Sound. Infestation rate and intensity (ciliate load copepod⁻¹), copepod body size and mating success were measured on six separate occasions in the field. Infestation rates exceeded 60% in both male and female copepods. Infested females had a significantly greater ciliate load than males on three of the six sampling dates. Infested males were significantly smaller than uninfested males midway through the event, whereas infested females were significantly smaller during the peak in infestation rate and intensity. There was no difference in the frequency of unmated females between infested and uninfested individuals on any sampling date. Laboratory experiments were carried out under three food regimes (starvation, food-limited and food-unlimited). Survivorship was significantly lower for infested versus uninfested males under starvation, but not under the food-unlimited condition. Infested females, however, showed significantly lower survivorship than uninfested ones under all three food regimes. In addition, infested females produced significantly fewer eggs than uninfested females under starvation and food-unlimited conditions. Overall, both male and female A. tonsa bearing the ciliate epibiont Zoothamnium experience a significant decrease in components of fitness.