Through DNA analyses, a puzzle that has confounded biologists for several decades has been solved, and a new species of leopard frog—as yet unnamed—has been documented.
I was first introduced to leopard frogs, as were most of us, in high school biology class. Leopard frogs were the frogs of choice for lab dissections.
In the spring of 1988, I had my second encounter with leopard frogs: during a late night excursion to Oyster Pond in Montauk with Larry Penny, Jim Cavanaugh, Andy Sabin and Mike Klemmens. In a small freshwater wetland adjacent to the main pond, we could hear the odd mating calls of the males, a combination of sounds best described as grunts, chuckles, snores and air-filled balloons being twisted and rubbed by hands.
Named for the dark, round spots found on their backs, leopard frogs are quite variable in coloration, spot pattern (the dark leg spots are often square and rectangular) and vocalizations. Outside of the mating season, and of course when not in their egg and larval stages, leopard frogs spend most of their active time on terra firma. From spring through early autumn, adults are found in meadows and fields hunting their favorite prey: crickets, grasshoppers, beetles, worms and assorted insects. They winter buried in the soft mud of marshes, pond and river bottoms.
The New York State Department of Environmental Conservation’s Herp Atlas Project lists the northern leopard frog as the most abundant and widely distributed of the two species, documented in 625 of the state’s 979 quadrangles and found in every county except those comprising New York City and Long Island. On the other hand, the southern leopard frog was documented in only 18 quadrangles and seven counties: Staten Island, Nassau, Suffolk, Putnam, Rockland, Orange and an oddly disjunct population in Seneca County near the Finger Lakes.
As the novice herpetologist among the crew, I listened quietly as the experts discussed and debated the nuances of these sounds in the dark. The puzzle revolved around whether the populations of leopard frogs in the Long Island and Metro New York area were northern leopard frogs (Rana pipiens) or southern leopard frogs (Rana sphenocephala). Long Island lies at the southern range limits of the former, and the northern limits of the latter.
My 20-year-old field guide lists five species of leopard frog in North America. There are probably double that number listed today. Leopard frogs are a confusing group. Author Tom Tyning writes, “It is easy to find leopard frogs with the characteristics of any given population anywhere in the country.” He states that releases of pet leopard frogs and laboratory animals outside their original ranges has added to the confusion.
Fieldwork relying on their distinctive mating calls seemed inconclusive, and Mike Klemmens wanted a specimen to bring back to the Museum of Natural History for a physical examination. As soon as we entered the pond with nets in hand, the chorus of sounds ceased, but somehow Larry managed to capture one in his net. Based on its external appearance, Klemmens announced that it was the southern leopard frog.
Two decades later, biologist Jeremy Feinberg took another look at the puzzle, this time armed with more advanced techniques in analyzing DNA samples, and he has been able to solve it. DNA work has revealed that they are neither southern leopard frogs nor northern leopard frogs but an entirely new species. Thus far, fieldwork has established the new specie’s range as a small area encompassing portions of New Jersey, Staten Island, Putnam, Rockland and Orange counties, and central Connecticut.
Unfortunately, leopard frogs no longer call from their historic sites in Montauk, the pine barrens, and other locations on Long Island, so we will never know for sure if these were also members of the new species. And why they disappeared is another mystery surrounding this group of amphibians.
Jeremy Feinberg is trying to locate old photographs of leopard frogs from Long Island. If anyone has photographs of this handsome frog, please contact Jeremy at firstname.lastname@example.org