A Little Bit More
For humans, any freezing of our tissues causes frostbite, an extremely dangerous and painful problem. But the Wood Frog (some other frogs can also do this) is able to avoid damage to its tissues even though it may be frozen solid during the winter. This ability to survive in the far north has greatly expanded the Wood Frog’s range and as a result, it is able to live in areas with little or no competition from other frogs. Once the temperature begins to stabilize above freezing, a hibernating Wood Frog’s heart begins to beat and then it begins breathing. Soon the frog crawls above ground and finds a shallow vernal (spring) pool where it will breed. While at a breeding location the males make a croaking sound that is not very frog-like and sounds more like ducks quacking than anything else. The arrival of these frogs is often so early in the spring that ice is still present in their chosen breeding site. Wood Frogs are considered explosive breeders since their breeding time may be for only a few days in length, sometimes just one, and then it’s over for that year. Once their eggs are laid, the adults leave the water and spread out into the surrounding area, often a considerable distance from any standing water. It’s easy to know whether Wood Frogs have visited a given pool if you see the masses of eggs they leave behind. Soon these hatch into tadpoles where they live for the next few months before transforming into land-dwelling adult Wood Frogs.
Although you may be an avid hiker in areas where Wood Frogs live, you probably have never seen one before. Wood Frogs have subdued colors that blend quite well with leaves and ground cover on the forest floor and they’re not at all easy to spot. Your best bet, if you want to see these beautiful amphibians, is to find a location where they breed in the spring and see them there.
Activities
Freeze and Thaw
Objectives: See What Freezing does to tissue
Materials: Fresh tomato, access to refrigerator and freezer, plate/dish
We’ve used this activity before but it works well and many of you probably haven’t tried it yet, so we’re making it available again.
There is an easy way to demonstrate the damage that freezing can do to living tissues.
1. Obtain a fresh tomato from the store and slice two thick slices from the middle.
2. Place each of the two slices on a plate (paper will do fine) and place one uncovered in the refrigerator and the other, uncovered in the freezer. Leave both in for approx. 24 hours.
3. Remove the two slices (make sure you know which is which but don’t let students know – you may want to label them “exhibit A” and “exhibit B”), allow them to stand at room temperature for an hour and then examine each.
4. Have students closely examine both slices. Allow them to use a pencil to gently press down upon each slice. It should be immediately obvious that the two slices are not the same anymore.
5. Now quiz the students as to which one is the “freezer” slice and ask them what they think has happened to make the freezer slice look as it does.
Answer: As the fluids in the tomato’s cells froze, the water expanded and ruptured cell walls allowing the contents to ooze onto the plate. This kills the ruptured cells and is therefore extremely dangerous if some protective measure hasn’t been taken. Although this is a demo on plant tissue, animal tissues are affected in much the same way but tend not to ooze fluids as easily.
You may want to note that although many plants, or parts of plants, are susceptible to freezing temperatures, many kinds of plants “prepare” themselves, much like the Wood Frog, for winter and their tissues are not damaged either. If you live in a temperate area of the world, the woody plants that surround you must avoid freezing damage each and every winter.
Key Concepts
Behavior and Regulation, Structures and Functions
Questions
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Posted by Pat Momich on March 04, 2006 at 11:02 PM
Q: What do newt eggs look like? We have red spotted newts in our pond, but to our knowledge we've never seen their eggs. The wood frogs are very active now with many large egg clusters. Thanks!
A: I thought I could go immediately to some photos of Red Spotted Newt eggs but was wrong - they're not at all common. I did get some info on them I'm including. Hope this helps.
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Oviposition can take several weeks, because the female will only lay a few, widely scattered eggs, each day. It's still uncertain whether or not females will lay all of their eggs in a breeding season, however they do lay between 200 and 400 single, jelly-covered eggs on submerged vegetation, each season. As soon as the process is finished, the female newt swims away leaving her eggs to survive on their own. The incubation of the eggs is somewhat dependent on temperature, but generally lasts from 3 to 8 weeks.
I thought they laid groups of eggs but apparently, they don't. So, you'll need to look for individual eggs in your pond if you're to see any. Good luck.
Posted by Don Cook on March 12, 2005 at 03:11 PM
Q: I just read the piece about over-wintering wood frogs. Here's my question: is a frozen wood frog alive?
A: Yes, the frog is definitely alive, otherwise it wouldn't be able to renew activity in the spring. It's life processes are just at a standstill although there may be a wee bit of "activity" going on within its body during this dormant period. Pretty impressive, huh!