Parasite-mediated effects on their host populations are strongly dependent on parasitic specificity, i.e., the strength of the interactions between them (Anderson and May, 1981). Fitness consequences of body-size-dependent host species selection in a generalist ectoparasitoid. Host species differ in their susceptibility to a certain parasite; therefore parasite transmission between species is often asymmetrical, where one host species might be highly infected resulting in a higher parasite load to the system (Woolhouse et al., 2001). Parvilucifera sinerae is a generalist parasitoid able to infect a wide range of dinoflagellates, including toxic-bloom-forming species.A density-dependent chemical cue has been identified as the trigger for the activation of the infective stage.Given that hosts can vary in their susceptibility to a certain parasite, and that host relative abundance in natural communities shift, parasite selection amongst host species is a very relevant question that has not yet been explored in great detail in parasitoid–phytoplankton systems. Dinoflagellates are a dominant group of eukaryotic phytoplankton and an important component in marine ecosystem functioning, playing a key role in primary production and the marine food web (Margalef, 1978; Reynolds, 2006). Instead, the parasitoids contact the host at random, governed by the encounter probability rate and once encountered, the chance to penetrate inside the host cell and develop the infection strongly depends on the degree of host susceptibility.
sinerae is able to sense potential hosts, but does not actively select among them.Together these traits make Parvilucifera-dinoflagellate hosts a good model to investigate the degree of specificity of a generalist parasitoid, and the potential effects that it could have at the community level.Here, we present for the first time, the strategy by which a generalist dinoflagellate parasitoid seeks out its host and determine whether it exhibits host preferences, highlighting key factors in determining infection.Dinomyces and Parvilucifera species (with the exception of P. prorocentri) have been described as generalist parasitoids, able to infect a wide range of hosts within dinoflagellates, including toxic species (Garcés et al., 2013a; Lepelletier et al., 2014a,b).