Not only that, but they found nicotine--the same chemical found in cigarettes--in one Mantella baroni frog out of 22 examined. Nicotine is produced by plants and can sometimes be found in animals that eat these plants. But so far no nicotine-producing plants have been found growing in the area where this frog was found. This was the first time researchers observed this phenomena and they are not sure how the chemical enters the frog's system.The second greatest use of nicotine after cigarettes is insecticides. I'll venture a wild guess that the frog ate insects exposed to insecticides.
Or second hand smoke.