I recently had the opportunity to experience the culinary qualities of one of my favorite animals. Bull Frogs are invasive and are the largest frogs in North America. My other experiences with frogs are with much smaller species. I worked as a research assistant in a frog behavior lab at the University of Minnesota for two years. The goal of the research was to determine the selectivity and sensitivity of the amphibian ear. In other words, how on earth does a female select and find a single male frog calling in a pond with thousands of other frogs with multiple species!
This call is deafening. After many nights in breeding ponds the calls of thousands of horny frogs resonated through my head hours after leaving the water. The frog calling above is a Cope’s Gray Treefrog (Hyla chrysoscelis) is one of two species of treefrog in Minnesota. The two species are physically indistinguishable, they look exactly the same! There are only a couple of way to tell the difference. First is the call. The Eastern Gray Treefrog (Hyla versicolor) has a slower more musical call and the Cope’s Gray Treefrog has a call that is twice as fast and is much more punctuated. Second, get ready for some biology, H. versicolor is tetraploid meaning it has four copies of each chromosome. H. chrysoscelis is diploid, like you and I, and only has two copies of each of its chromosomes. This means that despite the fact the two species breed in the same ponds at the same time they are physically incapable of reproducing due to the chromosomal difference. Even with all these differences the two species physically look exactly the same!
Both species of tree frog found here in Minnesota also have a couple of other interesting adaptations. First they can change color. Despite being called “Gray” treefrogs, both species can change color from dark gray to bright green (see picture above). Spending a lot time in trees, they need to adapt to life on a leaf or life on bark and they will change color to blend in.
Another amazing quality of these little frogs is their ability to freeze completely solid in winter. The frogs turn their blood into antifreeze which prevents the formation of destructive ice crystals despite being frozen completely solid. If you were to find a frog in winter and bring it inside. The little frogcicle would slowly thaw and eventually hop away! PRETTY SWEET!!
Up Next: More on Frogs!