On Gulf Coast Toads and the Changing of the Geni September 23, 2019

A Gulf Coast Toad hangs out on a rock in Fort Worth (photo by author).  Commonly found in a large part of Texas, it is emblematic of major taxonomical changes in the iconic toad family of Bufonidae.

On my bookshelf is a copy of the venerable Aububon Society Field Guide to North American Reptiles & Amphibians (11^th Printing, 1992).  I have had this copy since I was in junior high.  That was slightly more than a quarter-century ago.  Upon recently thumbing through the toad section, I found the photo entry for the Gulf Coast Toad.

My interest in this species was piqued because several weeks ago, I found the first one along my home here in the DFW Metroplex.  Last summer was the first time I had found (and photographed) one in the [sort-of] wild, having found one at the Fort Worth Botanical Gardens.  Naturally, I consider these “firsts” all kinds of cool, since this is a totally different species from the toads I grew up finding in southern Indiana.  There, the options were Fowler’s Toads and American Toads, mostly the former.  It’s a sign of finding different fauna in a different part of the country, which is something I find rather exhilarating.

Back to the Gulf Coast Toad entry in the Audubon Society Field Guide (entry 246):  on the explanatory pages (397-398), the species is listed as Bufo valliceps.  At this same time, the Fowler’s Toad was listed as B. fowleri, and the American Toad was B. americanus.  Indeed, the very genus of Bufo has been synonymous with toads themselves.

Not anymore.  The Bufo genus over the years had become a very cosmopolitan genus for toads.  Apparently, to a critical mass of taxonomists, the genus had become a little too cosmopolitan, and some species formerly within said genus have been spun off into their own geni.  For example, the Fowler’s and American Toads are now Anaxyrus fowleri and Anaxyrus americanus, respectively.  The Gulf Coast Toad now belongs to genus Incilius instead of Anaxyrus.  Since the species listed in the old Audubon field guide was B. valliceps, it would now logically be Incilius valliceps.

Except that it is not.  As it turns out, there are two types of Gulf Coast Toad:  to be more precise, two species that represent two different geographical populations.  I. valliceps, the ostensible representative of the Texas and Louisiana population (the northern population), is actually the species for the Mesoamerican population (that is, the southern population).  The Gulf Coast Toads found here in Texas are actually I. nebulifer.

All of this is a fairly recent development.  The northern population of Gulf Coast Toads went from Bufo valliceps to Incilius nebulifer in just 15 years.  Yes, many other toads found in North and Central America have also been reclassified into either Anaxyrus or Incilius.

Not to fret, though, Bufo fans:  the genus is still alive and well, and still represents 150 species within family Bufonidae.  The geni Anaxyrus and Incilius still belong to family Bufonidae as well.  Bufo also remains the genus for the largest known species of toad, the Marine Toad, a.k.a., the Cane Toad (B. marinus), which has become an invasive species in Florida (also found in extreme south Texas:  think McAllen and Brownsville).

In any case, it remains amazing to see how a species commonly found in much of Texas has had such a journey through taxonomical placement.  But the implications of these recent developments are potentially profound, for they serve as a reminder to all of us how nothing is static, and how little of science is actually “settled” science.