K S Vainutis, A E Zhokhov, M Urabe, A Aydogdu
The family Allocreadiidae comprises diverse parasites of freshwater fishes, but their evolutionary timescale remains poorly understood. We provide a molecular dating analysis based on an expanded 28S rRNA dataset and redescriptions of two East Asian species, Allocreadium hasu and A. pseudaspii, with new morphological and genetic data. Allocreadium hasu from Lake Biwa (Japan) is genetically close to Far Eastern A. khankaiense and A. anastasii (0.09-0.97% divergence in 28S) but has not been recorded in the Russian Far East. Allocreadium pseudaspii, first recorded in the Bolshaya Ussurka River, possesses eyespot remnants and occupies a unique position among European species, suggesting secondary eastward dispersal. Phylogenetic analyses confirm family monophyly and resolve relationships among Palaearctic genera. Divergence time estimates indicate the most recent common ancestor of Allocreadiidae originated in East Asia during the Lower Cretaceous (~110 Ma). Diversification of major genera coincides with radiation of primary fish hosts: Allocreadium with Cypriniformes (~93 Ma), Bunodera with Perciformes (~75 Ma), and Crepidostomum s. str. with Nemacheilidae (~49 Ma). The basal genus Acrolichanus, parasitic on sturgeons, diverged earlier (40-80 Ma). The split between the Neotropical genus Margotrema and its Palaearctic relatives is estimated at ~6.5 Ma, consistent with closure of the Panama Isthmus. Our results provide a temporal framework for Allocreadiidae evolution, linking diversification to biogeographic history of freshwater fish hosts in East Asia and subsequent dispersal to North America via the Bering land bridge and to South America through the Panama Isthmus.