by Greg Mayer
Since I first read about them when I was about 12 years old, I’ve been intrigued by the somewhat mysterious Vegas Valley leopard frogs. Known from a handful of springs, all in what is now more or less metropolitan Las Vegas, they had disappeared before the middle of the 20th century, and had been poorly known before apparently slipping out of existence. But now they’re back– sort of.
Evon Hekkala of Fordham University and her colleagues have a paper in press in Conservation Genetics in which, using DNA extracted from specimens of Vegas Valley frogs in the collection of the California Academy of Sciences, they find that Vegas frogs are closely related to the Chiricahua leopard frog of Arizona and nearby areas. In fact, the Vegas frogs are nested within the many samples of Chiricahua frogs they studied. From this they conclude that the Vegas frog is conspecific with the Chiricahua frog, and thus the Vegas Valley leopard frog is not extinct.
That the Vegas frogs (Rana fisheri) are conspecific with the Chiricahua frogs (Rana chiricahuensis) is a not unreasonable inference. North American leopard frogs, once thought to be a single widespread species, have proven to be a complex of several biological species, and although the situation is modestly clear in the eastern United States, there is much work yet to be done in the southwestern US and especially Mexico to figure out what’s going on. The Vegas frogs are not genetically identical to the Chiricahua frogs (contrary to some media reports), and, with only about 1200 base pairs examined at three loci, more differences are sure to be found.
So is the Vegas frog not extinct anymore? This isn’t just a biological species vs. amount-of-difference species concept question. One could accept, under various species concepts (and we know which one is right!), that the Vegas and Chiricahua frogs are conspecific, but still ask, is the Vegas Valley frog still extant because similar, but not identical, frogs continue to exist 100’s of kms away? I’m not sure. The US Endangered Species Act recognizes that population segments, even if they lack nomenclatural recognition or distinction, can be endangered, and be worthy of protection. And if a segment can be endangered, it can, of course, go extinct. So, while I’m glad we’ve learned who the Vegas Valley frogs’ closest relatives are, and that they’re quite similar, and that, due to the rules of nomenclature they will bear the name fisheri, I’m afraid the Vegas Valley frogs are still extinct.
The great herpetologists Albert & Anna Wright and Robert Stebbins summarized most of what will ever be known about the Vegas Valley frogs, and wrote, movingly yet scientifically, of their unsuccessful searches in the Vegas area in the 1940’s (they were last collected in January 1942, and last reported seen in the summer of ’42). The Wrights concluded:
Our R. fisheri may go with the old springs gone, the creek a mess.
Fisher, J., N. Simon, and J. Vincent. 1969. Wildlife in Danger. Viking, New York
Hekkala, E.R., R.A. Saumure, J.R. Jaeger, H.-W. Herrmann, M.J. Sredl, D.F. Bradford, D. Drabeck, and M.J. Blum. 2011. Resurrecting an extinct species: archival DNA, taxonomy, and conservation of the Vegas Valley leopard frog. Conservation Genetics in press. pdf
Moore, J.A. 1944. Geographic variation in Rana pipiens Schreber in eastern North America. Bulletin of the American Museum of Natural History 82:345-370. pdf
Pace, A.E. 1974. Systematic and biological studies of the leopard frogs (Rana pipiens complex) of the United States. Miscellaneous Publications, Museum of Zoology, University of Michigan 148, pp. 140. pdf
Stebbins, R.C. 1951. Amphibians of Western North America. University of California Press, Berkeley.
Wright, A.H. & A.A. Wright. 1949. Handbook of Frogs and Toads of the United Sates and Canada. Comstock, Ithaca, New York.
David Hillis of the University of Texas (who Jerry just mentioned) has done much of the work that has more recently both clarified, and pointed out the lacunae in, our understanding of leopard frogs. Many of his papers (on leopard frogs and many other subjects) are available here.
Update. David Hillis has kindly commented below, and quotes one of his papers (Hillis and Wilcox, 2005); here’s a link to the pdf of that paper.