The evolution of an ancient tapeworm lineage in its catfish hosts: vicariance, dispersal and diversification in Gangesiinae (Cestoda: Proteocephalidae)

The diversification of tapeworms of the subfamily Gangesiinae (Cestoda: Proteocephalidae), parasites of catfishes (order Siluriformes), is assessed using molecular and morphological evidence. A two-gene (lsrDNA and COI) phylogenetic analysis of all species of Gangesiinae (except Gangesia margolisi) resulted in a basal polytomy that included several lineages of Gangesiinae and Acanthotaeniinae. Palaeogeological events, along with host-shifting and dispersal, played prominent roles in the evolution of these tapeworms. Gangesia radiated through two major lineages in the Indomalayan and Palaearctic regions. Morphological changes during this radiation also included secondary loss of diagnostic morphological features of the genus, as in Gangesia mukutmanipurensis sp. nov., which lacks hooks and hooklets on its scolex. An updated key to the genera placed in Gangesiinae is provided and two new synonyms are proposed. A basal polytomy involving some of the potentially oldest lineages of Gangesiinae prevents firm conclusions regarding the ancestral area of origin of these tapeworms. Nevertheless, when the distribution and host-associations of Gangesiinae are considered in the context of the historical biogeography of their catfish hosts, the Indomalayan region appears to have been the ancestral homeland and a major centre of diversification of these tapeworms, with range expansions in western and northern parts of Eurasia and Africa.