Monday, July 31, 2017

Gulf Coast Toads in Alabama? Yep, Confirmed.


    It was dreadfully dry in the Southeast last fall, and many animals were hard to come by that season. But on a weekend hike with his family in Montgomery, Alabama, Roger Birkhead discovered something new and noteworthy.

    I’m sure they were relishing that day in true Birkhead form – tromping through the forest, rolling over logs, and catching many odd little beasts that they happened to encountered. And when Roger flipped over an old and desiccated board, they sure did find an odd little beast. It was a toad, but not any regular Alabama toad. After a quick double-take, Roger’s internal herpetology alerts fired off, and he recognized that it wasn’t one of the four usual Alabama toads. This particular one was strange. it had irregular and bold crests on its head, with dark pigmentation dotted in lines across it’s body.  Roger, being the keen natural historian that he is, collected it for further study at the Auburn University Museum of Natural History, and this is the story of how the first Gulf Coast Toad (Incilius nebulifer) was recorded in the state of Alabama.

    The Gulf Coast Toad has a pretty massive geographic distribution, which extends from basically Mexico City, Mexico, north along the Gulf Coast into Texas, and as far east as barely reaching into southern Mississippi. Now, one might think – “How did a Gulf Coast Toad doing in central Alabama, so far from the species’ native range in Texas, Louisiana, and Mississippi?!” Could this be a non-native population that has recently been introduced into Alabama? Potentially, yes. But also maybe not. While Montgomery is a considerable 300 mile stretch from the closest known populations in Mississippi, 300 miles isn't really that far of a gradient of ecological change for a species which spans latitudinal habitat from Mississippi all the way to Mexico City. 

    With this alternative viewpoint in mind, I can think of three hypothetical scenarios to explain the presence of this toad in Alabama. That specimen could have been: (1) a single, errant, non-native specimen, which jumped off a truck (or some-such random mechanism) and which does not represent a native breeding population, (2) a specimen which does represent a breeding population, but which is not native to the area and was recently established, or (3) a specimen which represents a breeding population, which is actually native, and has been here all along – and nobody ever noticed it! To eliminate one or more of these hypotheses, we need more data!

    Thus, my guy Roger was keeping his eye on the weather this past spring for a good rainy night to return to Montgomery and try his luck for more Gulf Coast Toads. And with weather forecasts predicting rain on May 12, Roger put out the call, and Craig Guyer and I joined in for the fun.

    The rain never came, but we gave it a good effort. Near the original forest locality from 2016, we heard a large and diverse chorus of the summer-breeding frogs – Green and Bird-voiced Treefrogs dominated the soundscape, but Banjo, Bull, and Cricket Frogs contributed as well. And we saw a big old cottonmouth: as always, more fearful in appearance than disposition. We visited a few such wetlands, striking out on toads, and settling instead for the occasional Dewberries.

    But the first locality wasn’t the only card we had to play. We had recently gotten a tip from an Auburn herpetology student, Dani Douglass, who had recently photographed a Gulf Coast Toad hopping around her suburban neighborhood, a few miles away from Roger’s spot. So, we shifted gears and tried our luck at the neighborhood.

    As soon as we pulled in, we scored our target and found a Gulf Coast Toad in the middle of the road. This toad was dead, a recent victim of traffic mortality, but we were pleased to be off the schneid with our mission for the night. We bagged it, and kept on hunting. We explored the neighborhood a bit, and then moved to an old field nearby – a classic country dump, with garbage and beer bottles all over the place (Roll Tide). And that’s where we found the third and fourth specimens – a pair of big, mature Gulf Coast Toads hanging out beneath a wooden palette.

    Now let’s think back to the three hypotheses I proposed earlier. These accumulating observations are now suggesting that there are certainly multiple populations of Gulf Coast Toads living around Montgomery, which reasonably eliminates the first scenario. Given that these toads appear to represent a reproducing population living in pretty sub-optimal habitat in and around neighborhoods, which most native species avoid, we are thinking that these toads represent a non-native species that has been recently established (the second scenario). This is consistent with other studies which have found Gulf Coast Toads to be invasive in human-modified habitats in Louisiana and Mississippi, where they have been outcompeting and displacing a native species, the Fowler’s Toad. In this non-native and invasive scenario, Gulf Coast Toads might be exerting negative effects on the native toad assemblage.

    But it’s hard to eliminate the third scenario. Perhaps the Montgomery toads represent a native, disjunct population, which has just overlooked all along. To be clear, I am very skeptical of this hypothesis, given what we know about the species being invasive in other states. But we now have tissue samples from the specimens, and it’s possible to perform a genetic analysis to determine whether (A) the populations are genetically linked to populations elsewhere in the species’ range, or (B) if they represent a population with it’s own unique evolutionary history. The former result would suggest a human-mediated introduction of Gulf Coast Toads to the herpetofauna of Alabama, while the latter would suggest that the Gulf Coast Toad is a native and overlooked species in the state. An intrepid undergraduate or high school student should take up this project!


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