Toads and other amphibians are great examples of resilience. They were on the Earth before the dinosaurs and are still here. Fall is a great time to see toads. They are trying to find good places underground to spend the wintrer.
This year they are acting strange, though. They are already burying themselves to hibernate when its 90 degrees during the day. They love the nice loose soil of my garden beds. Up north, where the soil freezes deeper, I never found them buried in the garden. Here in Arkansas, I unearth several every Spring. It’s easy for toads to get deep in the tilthy, fluffy soil in beds. So I get plenty of toads and have to be careful when I’m turning over the beds in the spring.
Unearthing them when its so hot is new this year What is going on with the toads? One thing for sure, they’ve got a reason. They must know something about survival and resilience since they preceded and outlasted the dinosaurs and are invading some places. Unfortunately, the reason may be daylight and the cool days we had in August stimulating hormones which fit the more usual climate.
In the US and other industrialized countries, climate changes or something is causing amphibians to decline precipitously, beginning in the 1950s. But even in the US, they are doing OK where they don’t encounter the products of industrial life–such as at Meadowcreek. Just come and listen to our spring peepers.
Amphibians’ current problems in industrialized countries are well documented. Some say amphibians are among the most threatened creatures on the earth today. More than one third of species are considered to be threatened with extinction and over one hundred and twenty are believed to have become extinct since the 1980s. See this article for details. It turns out a lot of the ballyhoo may have underestimated the resilience of toads and their relatives. They are probably just even a little more resilient to the mass extinction currently being caused by man.
The concern for amphibians began in the mid-1990s when people in the United States and Canada began to notice frogs in their local ponds were sprouting extra legs or fewer legs. Minnesota state government got hundreds of calls from 54 out of 87 counties.
Citizens and scientists alike feared that whatever was altering the frogs–pesticides perhaps–was also having an effect on humans. But researchers didn’t find any compelling link between frog deformities and humans diseases such as cancer. Turns out the frogs were getting their legs naturally.
A flatworm called Ribeiroia starts out life in snails. It grows and reproduces inside the snails, which it castrates so that they don’t waste time on making eggs or looking for a mate. In its castrated host, the parasite produces a new generation of flatworms that can escape the snail and swim in search of a vertebrate host. They typically infect fish or tadpoles. When they invade tadpoles, the parasites bury themselves in the tiny buds that will eventually grow into legs.
As the frogs develop their legs, the parasites wreak havoc. In some frogs they will stunt the growth of a leg, leaving it a stump. In other frogs, a developing leg forks in two. A single frog may even sprout a dozen legs. How do they do it?
In order for a limb bud to develop properly, its cells have to produce certain molecules. The molecules spread out across the limb bud, causing other cells to make other molecules, to grow faster, to die off, and to do all the other things required to make a limb.
One of the crucial molecules for building legs is a version of Vitamin A, known as retinoic acid. Before the swimming parasites find a tadpole, they are producing retinoic acid. Once they’re buried in the frog’s limb bud, their level of retinoic acid drops. Meanwhile, the level of retinoic acid in the limb bud shoots up 70 percent. All of these findings are consistent with the idea that the parasite is injecting limb-deforming drugs into their host.
The deformities of the frogs are part of a strategy that the parasite uses to advance its life cycle. The frog is just a way station for the parasites. They cannot mate or reproduce in frogs. Instead, they have to wait to get into a bird, where they take up residence in the gut and produce eggs that are shed by their host. And they can only make that trip if the frog they inhabit is caught by a bird. Frogs with deformities are more likely to get caught by birds and eaten.
Frogs that live in water contaminated with high levels of fertilizers were more likely to be infected with Ribeiroia. So the fertilizer run-off from farms can lead to deformed amphibians due to stimulation of Ribeiroia infection . That’s why we never had such problems at Meadowcreek. We don’t have fertilizer run-off into our ponds, just mostly spring run-off.
Those who predicted amphibians demise may be surprised.
Toad resilience is most apparent in Australia. The cane toad arrived in Australia 75 years ago. Initially they spread at the rate of 6 or so miles per year, traveling solely at night. Now they have adapted and are spreading at up to 35 miles per year.
The toads activity levels, relative leg length, and stamina have all changed. They remind me of how immigrants get taller and stronger when they come to the US than their ancestors were in the old country.
American toads and frog are easily distinguished, though the common names don’t fit all the species. Frog common names refers to species that are aquatic or semi-aquatic and have smooth, moist skins; the term “toad” generally refers to species that are terrestrial with dry, warty skins. But there are plenty of exceptions to these rules, if you want to really study frogs and toads.
American toads (Bufo americanus) and other frogs that are good diggers burrow deep into the soil, safely below the frost line. Some frogs, such as the wood frog (Rana sylvatica) and the spring peeper (Hyla crucifer), are not adept at digging and instead seek out deep cracks and crevices in logs or rocks, or just dig down as far as they can in the leaf litter. These hibernacula are not as well protected from frigid weather and may freeze, along with their inhabitants.The fact that this small amphibian can overwinter on the forest floor with little more than a layer of leaves or logs, is nothing short of a miracle.
Why don’t they freeze? Ice crystals do form in such places as the body cavity and bladder and under the skin, but a high concentration of glucose in the frog’s vital organs prevents freezing. A partially frozen frog will stop breathing, and its heart will stop beating. It will appear quite dead. But when the hibernaculum warms up above freezing, the frog’s frozen portions will thaw, and its heart and lungs resume activity.
We put up wood for the winter. caulk our doors and windows, find our coats and long underwear. Too bad we can’t just generate some antifreeze and stay outside all winter.
For more on how you can try to be as resilient as an amphibian, read our free on-line book by cllcking this phrase.