Hi, my name is Jennie. I’m an intern, on loan to the lab through Northeastern University’s co-op program. I spent March through May working at Penn State, assisting with a variety of projects in progress and conducting some independent research with Tracy’s guidance and support. I then tagged along on the lab’s second field excursion this past summer season, and I worked with a subset of the Langkilde cohort at the Solon Dixon Center in Alabama. Though much of my time was spent assisting with projects of the lab team , my personal research involved conducting experiments using Gastrophryne carolinensis, the Eastern Narrow-mouthed Toad, (which is actually an unusual type of frog, in the family Microhylidae).
These little guys are fossorial, burrowing about pointy face first under logs and other cover. The summer is their reproductive season, when they can also be found in or around water by the males’ charming call – a high-pitched “waaaaaaaaaah” reminiscent of a sheep in distress or a cellphone vibrating on a countertop. They are ant specialists, with resilient, slimy skin and a protective turtle-neck like fold above the head to defend them from their prey. It has also been suggested that the gooey coating Gastrophryne secrete may contain defensive compound(s); one hypothesis suggests that these compounds originate from the venoms or toxins in the ants that they eat which may then be sequestered by the frogs.
G. carolinensis are a species of interest for the Langkilde Lab because their range overlaps with areas invaded by fire ants. In addition to displacing other species of ants which Gastrophryne typically eat, fire ants might impact the survival of individuals. It is clear that fire ants can damage Gastrophryne despite their specialized skin (they often have visible lesions after stings), but these frogs appear to be doing pretty well in invaded areas, as evidenced by their abundant calling, despite feeding on fire ants.
To examine whether the goo secreted by Gastrophryne might be an effective deterrent to fire ants, I designed the following experiment:
1) Catch a bunch of Gastrophryne. This necessitated extended, rapid log flipping in broiling heat and wading into flooded roadside ditches – 1 million thanks to Sean, Chris, and both Marks for their invaluable help!
2) Put out yummy baits to attract fire ants, see previous post.
3) Place a swab adjacent to the bait. I am comparing 4 types of swabs, rubbed thoroughly on one of the following: a Gastrophryne, a hotdog (which should attract the ants as a food source), some water (as a control) or a Hyla chrysoscelis, the Cope’s gray tree frog which definitely secretes something unpleasant (as do many amphibians; independently confirmed for these guys by the persistent burning sensation in my Smilax wounds after handling them).
4) After 30 seconds, swiftly reclaim the swab and count the number of fire ants on it.
5) After repeating 3) and 4) ad infinitum, collect the bait and pop it in the freezer to allowing counting of the foraging ants, so variation caused by the number of ants present can be accounted for.
I’m starting to process the data from this experiment, but I expect that: 1) the swabs with hotdog residue should have the most fire ants on them, and 2) if the secretions of the narrowmouth toads and treefrogs are indeed noxious to fire ants, that those swabs should have the fewest fire ants on them. We’ll see how the data analysis works out!
As is generally the case when implementing a new experimental procedure, I shortly encountered an unforeseen complication – Gastrophryne get pretty dried out after being swabbed multiple mornings in a row. Additionally, when given time to regenerate their goo in captivity on a diet of termites, they preliminarily appear to be more attractive to the ants. Interesting! Maybe in future experiments we can examine how diet influences the noxiousness of Gastrophryne goo!
A second experiment I attempted was to evaluate feeding preferences of Gastrophryne for different species of native ants and fire ants collected around the Dixon Center. I was hoping the Gastrophryne would actively hunt when presented with a bevy of ants, so I could see if they preferred a particular species. However, when placed in their novel Gladware environments they seemed too distracted to do anything but attempt escape or tuck into a corner…Poor little buddies! I got to see them zap any ants that blundered into their vicinity though; that was pretty neat.
On this summer’s trip, I was able to do all kinds of cool field biology, have a lot of fun, and learn constantly (being beleagueringly uninformed compared to my herpetologist compatriots, whose patience with my inexperience is greatly appreciated!) – Thanks to the Langkilde Lab for providing me with such an awesome opportunity!