Polymorphisms in the sequences of <i>Marteilia</i> internal transcribed spacer region of the ribosomal RNA genes (ITS‐1) in Spain: genetic types are not related with bivalve hosts

Abstract Marteilia refringens is a protozoan parasite causing a disease notifiable to the Office International des Epizooties (OIE) and its distribution has implications for the transfer of live animals. The internal transcribed spacer‐1 (ITS‐1) from Marteilia clones contains polymorphism. Digestion with Hha I reveals two different restriction profiles, previously referred as ‘O’ ( Marteilia from oyster or Marteilia refringens ) and ‘M’ ( Marteilia from mussels or Marteilia maurini ). The aim of the present work was to determine whether the two previously described Marteilia molecular types (O and M) exist in the Iberian Peninsula and the strictness of the association with their bivalve host species. The sequence variability in the ITS‐1 of Marteilia species was studied in mussels, Mytilus galloprovincialis , and flat oysters, Ostrea edulis , from different geographical locations in Spain, to establish the existence and the distribution of different species or molecular types. Although there were two distinct evolutionary lineages that corresponded more or less strictly with the ‘M’ and ‘O’ types, it was evident from the estimated phylogeny that some ‘O’ types have switched to ‘M’ type, and vice versa. Moreover, ‘O’ types were found in mussels and ‘M’ types were found in oysters, which suggests that there have been several cross‐species transmissions of Marteilia between mussels and oysters.