Paedomorphisis is a pattern of developmental change in which an organism evolves to retain juvenile traits into its adult, sexually mature stage. This is a recurring evolutionary pattern in some groups of animals, with different but related lineages often separately developing the same traits in this way. One such group is the Lungless Salamanders (Plethodontidae), a group which has repeatedly produced species that are capable of breeding while retaining juvenile traits (such as tailfins and external gills) into adult life, some species (such as the Mexican Axolotl) having lost the adult stage altogether.
In a paper published in the journal Zootaxa on 11 April 2014, Michael Steffen of the Department of Biological Science at the University of Tulsa, Kelly Irwin of the Arkansas Game and Fish Commission and Andrea Blair and Ronald Bonett, also of the Department of Biological Science at the University of Tulsa describe a new species of Paedomorphic Salamader from the Ouachita Mountains of Arkansas.
The new species is placed in the genus Eurycea, and given the specific name subfluvicola, meaning 'dwelling bellow a stream', a reference to the habitat where the Salamander was encountered. The species was first discovered during a study of the related Eurycea multiplicata, when an apparently juvenile female was captured, with eggs developing internally. Since Eurycea multiplicata has never been recorded to breed prior to reaching full sexual maturity, this specimen was retained, and subjected to a DNA analysis, which revealed it to be a quite separate species.
Eurycea subfluvicola, female specimen in dorsal and ventral views. Note the developing eggs visible through the skin, particularly on the ventral surface, and retained external gills. Steffen et al. (2014).
After the first specimen was discovered, a further eight members of the species were located, all in an unnamed tributary of Slugger Creek in Lake Catherine State Park in Hot Spring County, Arkansas. Eurycea subfluvicola has a flatter profile than Eurycea multiplicata, but this could easily be missed if the existence of the species was not known, making Eurycea subfluvicola effectively a cryptic species, hidden within the juvenile population of Eurycea multiplicata.
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