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Maine's Vernal Pools Still Revealing New Secrets
08/05/2013   Reported By: Murray Carpenter

Biologists have known for a long time that Maine's vernal pools are important breeding grounds for amphibians. But even after decades of study, the pools that are raucous with frog calls in early spring and dry by late summer are still revealing their secrets. Now, researchers are studying one of their lesser-known denizens. Murray Carpenter reports.

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Maine's Vernal Pools Still Revealing New Secrets
Originally Aired: 8/5/2013 5:30 PM
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salamander 6 (1 of 1)

Kristine Hoffman (above) and two field assistants are walking back into the woods to check their traps around a vernal pool near Orono. It's a trip she has taken daily since early April, to check a series of pools she has encircled with fabric fences.

salamander 10 (1 of 1)"So when the salamanders go to breed into the pool, they hit this block, and they will follow it along," Hoffman says. "About every 10 feet we have a coffee can sunk into the ground that is level with the surface. So the salamanders will walk along, they will hit this fence, and they walk along the fence until they've fallen into one of the coffee cans, and then they get stuck there until we come by and look for them in the morning."

Hoffman is a Ph.D. student at the University of Maine. The salamanders she is studying are not the spotted variety which are so conspicuous in early spring in many parts of Maine, with big yellow spots on their backs. She is studying blue-spotted salamanders, which are less understood.

But today, the juvenile blue-spotted salamanders have yet to emerge from the pools, and Hoffman is finding wood frogs in her traps instead. The tiny little frogs are hopping away from the ponds, just starting their terrestrial lives. Some still have their tadpole tails (below).

salamander 4 (1 of 1)"Wood frogs are one of the first tadpoles to metamorph into adults and to leave the ponds," she says. "And they have to do that because if they don't, the pool's going to dry up and they're going to lose all of their reproduction."

Hoffman says this compressed life cycle is a trade-off the amphibians make in order to take advantage of these fish-free pools. Though they are devoid of fish, other predators visit the pools often, looking for protein-rich meals. This year, barred owls and snapping turtles have come calling, and a bear stopped by for a snack.

"We can tell you that bear and deer and moose use these pools a great deal," says University of Maine professor Aram Calhoun, one of Hoffman's advisors. "The animals that breed in thise pools and then go out into the forest provide food for a lot of other wildlife species that are important to Mainers."

Calhoun says Hoffman's research is part of the interdisciplinary Sustainability Solutions Initiative that is designed to bring science to action. In this case, understanding the ecology of vernal pools will help planners know which lands to conserve, and which might be appropriate for development.

"It is important to understand the particular habitat needs of blue-spotted salamanders because they are the least studied of the vernal pool amphibians," Calhous says. "We have a lot of information on wood frogs. We have a lot of information on spotted salamanders. But we can not expect efficient management of these species if we don't know the habitat needs of all of the animals involved."

Back in the field, after checking their traps, Hoffman and her assistants assemble a hand-held antenna. In April, they implanted little radio transmitters, smaller than pencil erasers, in 14 adult salamanders. And they have been tracking their movements ever since, to understand their habitat needs.

Listening for a strong signal, the team locates two of the salamanders beneath tree stumps, where they use the tunnels left by rotting roots. They find another beneath an old piece of wood, in a tunnel left by a mouse or another rodent.

"And she is just sitting in one of those tunnels," Hoffman says. "She's maybe five inches long, she's a black salamander with little blue snowflakes along her sides."

Plump, moist, and tastefully speckled, Emily, as she's been nicknamed, has moved nearly 300 meters from the pool where she laid eggs in April, and moved nearly 200 meters in just one night. This has been one surprise, says Hoffman - the salamanders are moving farther and faster than expected.

The other surprising finding is more complicated: Like most of the blue-spotted salamanders in Maine, a DNA sample showed Emily belongs to a lineage that has one or more extra sets of chromosomes. To better understand so-called polyploid animals, Hoffman had planned another experiment.

"So we set up this breeding experiment. We were going to have 100 males and 100 females, put them together in a bucket, see what eggs they produced, do the genetics on the adults, and see if we could tell them apart," she says.

But something strange happened: Hoffman found 700 adult female blue-spotted salamanders at the four pools - and only five males. No one is sure why. And it suggests just how much there more there is to learn about the ecology of Maine's vernal pools.

Photos:  Murray Carpenter


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