Reptile & Amphibian Forums

Hyla regilla has been traditionally classified as a species of Hyla quite simply because it has well developed toe pads plus other similarities to members of the genus Hyla. Recently Hedges (1986) transferred this species to Pseudacris on the basis of molecular distance data, which shows this species to be closely related to Pseudacris. Hedges's data is contradicted by that of Maxson and Wilson, which shows Hyla regilla being more closely related to Hyla arborea than it is to Pseudacris triseriata. There is also a new study which has been accepted for publication by the journal "Molecular Phylogenetics and Evolution" but this study, by Emily C. Moriarty and David. C. Cannatella, does not include Hyla arborea. Since Hyla arborea is the type species of Hyla, transferring Hyla regilla to Pseudacris means that Hyla arborea would probably have to be transferred to Pseudacris as well. But doing so would render Pseudacris an invalid genus, since Hyla has priority over Pseudacris. Therefore, if the genus Pseudacris is to remain valid, Hyla regilla would almost certainly have to be excluded. My hypothesis is that Hyla eximia is ancestral to the Holarctic treefrogs, including Hyla regilla and Hyla arborea. My hypothesis is consistent with the molecular data. Hyla regilla is in turn ancestral to the genus Pseudacris and to Hyla arborea. The genus Pseudacris can remain monophyletic if Hyla regilla is excluded. The genus Hyla would be paraphyletic. But that is an unavoidable consequence of recognizing the genus Pseudacris. Transferring H. regilla does not change this fact. Since paraphyletic groups are the inevitable result of the process of evolution, neither the Darwinians nor I have a problem recognizing paraphyletic taxa. The Hennigians, OTOH, would have a problem with paraphyly. Perhaps it is a good excuse for them to splinter Hyla. But that is another story.

According to Maxson (1978), Hyla cinerea, Hyla arborea and Hyla regilla form part of an unresolved polytomy on the basis of immunological distance data. That means Hyla arborea was part of an adaptive radiation of nearctic treefrogs that included a number of other species. Hyla arborea is the only one of this radiation to make it to the Old World, presumably across the Bering Land Bridge connceting the New World and Asia. That means the taxonomic proposal by Hedges and others to transfer Hyla regilla to Pseudacris simply cannot be done because Hyla arborea and Hyla cinerea would also have to be transferred to Pseudacris. But since Hyla arborea is the type species of Hyla and since Hyla has priority over Pseudacris according to the rules of the ICZN, the name Pseudacris would then become a junior synonym of Hyla.