PATTERNS IN HOST RANGE FOR TWO STRAINS OF <i>AMOEBOPHRYA</i> (DINOPHYTA) INFECTING THECATE DINOFLAGELLATES: <i>AMOEBOPHYRA</i> SPP. EX <i>ALEXANDRIUM AFFINE</i> AND EX <i>GONYAULAX POLYGRAMMA</i>¹

Abstract

The endoparasitic dinoflagellate Amoebophrya ceratii (Koeppen) Cachon uses a number of its free‐living relatives as hosts and may represent a species complex composed of several host‐specific parasites. Two thecate host–parasite systems [ Amoebophrya spp. ex Alexandrium affine (Inoue and Fukuyo) Balech and ex Gonyaulax polygramma Stein], were used to test the hypothesis that two strains of Amoebophrya have a high degree of host specificity. To test this hypothesis, a series of cross‐infection experiments were conducted, with 10 thecate and three athecate dinoflagellate species as potential hosts. Surprisingly, the two strains of Amoebophrya lacked host specificity and had wider host ranges than previously recognized. Among the host species tested, Amoebophrya sp. ex Alexandrium affine was capable of infecting only species of genus Alexandrium ( Alexandrium affine , Alexandrium catenella , and Alexandrium tamarense ), while the parasite from Gonyaulax polygramma infected species covering five genera ( Alexandrium , Gonyaulax , Prorocentrum , Heterocapsa , and Scripsiella ). In the context of previous reports, these results suggest that host specificity of Amoebophrya strains varies from extremely species‐specific to rather unspecific, with specificity being stronger for strains isolated from athecate hosts. Information on host specificity of Amoebophrya strains provided here will be helpful in assessing the possibility of using these parasites as biological control agents for harmful algal blooms, as well as in defining species of Amoebophrya in the future.