I have just spent the past week collecting leopard frog toes in western Illinois, from which I plan to extract DNA for genetic analysis. I survived lightening storms, mosquitoes, snapping turtles, snakes, coyotes, encounters with local law enforcement, and the peculiarities of rural culture hundreds of miles from the part of the state that elected Barack Obama. Armed with a dip net, a headlamp, a pair of scissors, and a bottle of Everclear (to sterilize the scissors, not to consume), I stalked ponds and flooded roadside ditches at night looking and listening for specimens. Although toe-clipping is unpleasant, it is the least-invasive way to reliably get large quantities of DNA in the field, while simultaneously marking frogs so you know if you happen to catch a repeat victim (not possible with other methods like buccal swabbing). The locals were generally indifferent to my presence, since both fishing and bullfrog gigging are common regional activities, and I just looked like a normal guy with a net. When they found out what I was really up to, they were amazed that I would think to travel all the way to they neck of the woods for research, and they helped me herp and gave me beer.
My first site was in Jackson County, Illinois, on the fertile Mississippi River floodplain. I was seeking plains leopard frogs, Rana blairi, and southern leopard frogs, R. sphenocephala. These closely related species can be distinguished by their spot pattern, the lay of their dorsolateral skin folds, and their call. R. sphenocephala has a rapid call which sounds frustratingly like a taunting laugh while they’re evading capture; R. blairi produces a slower, softer cluck. This muddy countryside on the cultural and biogeographic border between the Midwest and the South was an ideal place to look for a wetland supporting both species. I found a few individuals of both in a roadside ditch one evening, and I decided to try to collect full population samples there (to do population genetics, you need populations… usually at least 20 specimens). Unfortunately, there weren’t a lot of frogs in that ditch, and after three nights I had only collected a handful of each species. I did encounter many other neat amphibians, including bullfrogs, cricket frogs, toads, and a lesser siren (a foot-long eel-like aquatic salamander with no back legs, apparently named after the mythical seductive women of the sea by the same guys who thought that manatees look like mermaids). Each night I hunted until the wee hours of the morning, when I would return, exhausted and blairi-eyed, to my campsite. Thus, I am extremely fortunate that a fellow herp enthusiast happened to see me on the side of the road. He directed me to some ponds less than a mile away, where veritable plagues of both species were calling. In two more nights, I had easily collected more than I needed.
Next, I traveled north to Pike County, Illinois, looking for pickerel frogs (Rana palustris… actually another member of the leopard frog posse). R. palustris is a very attractive frog, with paired, square dorsal spots and bright yellow underparts. It often takes shelter in caves, so I searched along a stream near a cave, where other herpetologists have had great success finding this species. Almost all the frogs were located in a very specific section of the stream, suggesting that there could be a frog-sized entrance to the cave there that they are using. Also, in addition to the standard cricket frogs, bullfrogs, and toads at the site, I found several long-tailed salamanders.
To assess geographic variation in these species, I’m going to collect samples in other Midwestern states during the next few weeks. Updates to follow…