A new Anguilla species and a reanalysis of the phylogeny of freshwater eels

Evidence of a new species of Anguillid eel, Anguilla huangi sp. nov., was obtained from examining eel specimens collected from the Cagayan River estuary, northern Luzon I., the Philippines. Both glass eels and cultured eels reared in Taiwan for 5 yr were examined. The morphological measurements of A. huangi sp. nov. overlap with those of A. celebesensis Kaup, 1856 and A. interioris Whitley, 1938, so that this new species cannot be distinguished using morphological characteristics alone. We sequenced its complete mitochondrial genome and constructed a phylogeny of all currently recognized freshwater eel species and subspecies based on both molecular and morphological data. Although A. huangi sp. nov. seemed to be morphologically more similar to A. celebesensis, the molecular phylogeny showed a strongly supported clustering of A. huangi sp. nov. and A. interioris. The genetic distance between A. huangi sp. nov. and A. interioris was similar to that between A. anguilla (Linnaeus, 1758) and A. rostrata (Le Sueur, 1817). The distinct molecular phylogeny ensures the specific status of this new freshwater eel. On the other hand, based on the likelihood analyses, the phylogeny of freshwater eels seems to be better represented by polytomies. These polytomies are likely derived from multiple radiation (rapid speciation) events. We further inferred that each radiation event may also have included a large-scale expansion in distribution. The morphological phylogenetic tree generated using the minimum network (MinNet) method was generally consistent with the molecular phylogeny. We also propose a possible evolutionary history for freshwater eels. The Central American Isthmus hypothesis for the dispersal route of the Atlantic eels was supported by various lines of evidence.