Position of Pholeter gastrophilus, Braunina cordiformis and Ogmogaster antarcticus, parasites from cetaceans, in the molecular phylogeny of the Digenea.

FRAIJA, N.; CRESPO, E. A.; ANTONIO RAGA, JUAN; AZNAR, F. J.; FERNANDEZ, M.

Congreso; XITH EUROPEAN MULTICOLLOQUIUM OF PARASITOLOGY (EMOP XI); 2012

Cetaceans harbor a specific fauna of digeneans that include Braunina cordiformis (Brauninidae), Pholeter gastrophilus (Heterophyidae), species of Ogmogaster (Notocotylidae) and species of the Brachycladiidae. Braunina cordiformis and P. gastrophilus are gastric parasites of odontocetes, species of Ogmogaster inhabit the intestine of baleen whales and species of the Brachycladiidae occur in the digestive tract, bile ducts or air sinuses of odontocetes or baleen whales. Data about the phylogenetic position and evolutionary history of digeneans from cetaceans is currently available only for the Brachycladiidae. In this study we determine the position of B. cordiformis, P. gastrophilus and O. antarcticus in a previous molecular phylogeny of the Digenea. The analysis was based on the 18S and 28S genes of 164 digenean taxa sequences comprising 78 families. Species of Aspidogastrea were used as outgroup. A Bayesian inference was made under a model of nucleotide substitution (general time reversible GTR with among-site rate heterogeneity) that was considered the best estimate of phylogeny. Results showed two major clades with good nodal support based on posterior probabilities: Diplostomida and Plagiorchiida. Braunina cordiformis was placed within the Diplostomata, together with Strigeidae and Diplostomidae, whose members parasitize birds and mammals, whereas Pholeter gastrophilus and O. antarcticus were included within the Plagiorchiida. Pholeter gastrophilus shared its phylogenetic position with members of the families Opisthorchiidae, Cryptogonimidae and Heterophyidae, whose members are parasites of birds, mammals and marine and freshwater fishes. In a second phylogenetic analysis based on both 18S and ITS2 regions that included nine taxa of the Heterophyidae and Opisthorchiidae, P. gastrophilus was placed as the sister taxa of Pygidiopsis and Phagicola, which are common parasites of aquatic birds and carnivores. Interestingly, Ogmogaster antarcticus was included within a clade along with the Rhabdiopoeidae, the Labicolidae and the Opisthotrematidae, which are all parasites of sirenians. Overall, these results would suggest that the associations between cetaceans and their digeneans would have originated via host switching events, lending support to the hypothesis that the ancestors of cetaceans probably lost parasites of terrestrial origin during the hosts? transition from the land to the sea. This study is supported by grants CGL2009-07465, CGL2012-39545 (MINECO) and 2011-040 (Generalitat Valenciana).