European phyllodistomum (Digenea, Gorgoderidae) and phylogenetic affinities of Cercaria duplicata based on rDNA and karyotypes

Abstract

Genetic markers of some European Gorgoderidae species, including potential adults of Cercaria duplicata, were obtained and used to clarify phylogenetic affinities within the genus Phyllodistomum and to verify conflicting data existing on their life cycles. Molecular data and karyotype, 2n = 18, provide further support for ascription of C. duplicata to the Gorgoderinae. Sequences of C. duplicata form a robustly supported major clade, phylogenetically distinct from other known gorgoderid species in both ITS2- and 28S-based phylogenetic trees. The molecular data revealed no match between C. duplicata and any species of Phyllodistomum, including adults found in the experimental studies. One of them, P. elongatum, showed no differences from type species P. folium. Other, P. angulatum, forms a robustly supported clade, which is closely related to P. macrocotyle clade in all phylogenetic trees. This study supports the concept that only P. macrocotyle is a parasite of Dreissena polymorpha among the phyllodistomes and life cycle described for the type species P. folium by Sinitsin (1905) can apparently be discounted. Previously reported low host specificity of P. folium was justified. Adults of P. folium were detected in eight teleost species from five families and four orders. Cystocercous cercariae of P. folium were recorded in sphaeriid bivalves of the genus Sphaerium and Pisidium. According to our molecular data, P. simile, parasite of bullhead, must be regarded as synonym of P. folium. Phyllodistomum umblae is most closely related to P. folium in the all phylogenetic analyses. Molecular phylogenies support a presumption that Phyllodistomum species with cystocercous cercariae developing in sphaeriid bivalves should be regarded as Phyllodistomum sensu stricto. The results reveal a clear need for reconsideration of the knowledge on gorgoderid life cycles based on experimental studies and re-evaluation of the validity of some nominal Phyllodistomum species.