Evolution and phylogeography of the tubenose goby genus Proterorhinus (Gobiidae: Teleostei): evidence for new cryptic species

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Cryptic taxa present unique difficulties in the description of biological diversity, which DNA sequencing approaches often readily resolve. The tubenose goby Proterorhinus, along with other Ponto-Caspian fauna, has undergone recent Eurasian range expansion, as well as colonized the North American Great Lakes in 1990. We analysed mitochondrial (cytochrome b and cytochrome c oxidase subunit I) and nuclear (recombination activating gene 1; RAG1) DNA sequences and morphological characters from exotic Great Lakes as well as introduced and native Eurasian populations of Proterorhinus marmoratus (Pallas) sensu lato to assess their species identity and biogeographic patterns. The results obtained show marked genetic and morphological divergence that indicates species-level separation between fresh water and marine/brackish lineages, dating back approximately 3.82–4.30 million years. In addition, freshwater lineages within the Black and Caspian Sea basins show significant genetic and morphological differentiation, corresponding to an estimated 0.92–1.03 million years. We describe new evidence to support at least three separate species: the original P. marmoratus in marine and estuarine habitats within the Black Sea, a freshwater species in the Black Sea basin that was introduced to the North American Great Lakes, and another freshwater species inhabiting the Caspian Sea/Volga River basin. The freshwater tubenose goby in the Black Sea basin originally was described as Proterorhinus semilunaris (Heckel), and this is confirmed to be a valid taxon. The Caspian basin taxon may correspond with Proterorhinus semipellucidus (Kessler), a putative freshwater species in the Caspian basin that was originally described from a single specimen.