Загадочная метаморфоза: как за два дня лягушка-древолаз превращается из головастика в земноводное

It’s In Your Nature: Metamorphosis, amphibian style Metamorphosis: to change body form. We are all pretty much aware of the process of how a caterpillar makes the slow transformation into a butterfly or moth. The most commonly known, and the one most familiar to us, is the monarch butterfly. But it is not only insects that use metamorphosis; so do amphibians. And their transformation is sometimes faster and more dramatic. In today’s column, I’ll take us through the life cycle of our Eastern American toad. As the early spring temperatures rise, male toads emerge first from their hibernation. That could be from the bottom sediment of a pond or stream, or from the soft soil beneath the forest floor leaf litter. The male toads make their way to a pond, stream or even large mud puddle (usually from where they were born) and begin trilling. The trilling is the signal for the later emerging female toads to join them. The female, now carrying more than a thousand eggs, is ready to mate. As she lays long, stringlike “jelly covered” eggs, his sperm externally fertilizes them. The stringlike eggs are often intertwined among underwater weeds. In four to 14 days the eggs begin to hatch and small (about a half-inch-long) black tadpoles begin swimming about the water seeking algae. At this stage, they have a small mouth with tiny, sharp teeth to scrape the algae. Some sources claim this tadpole stage lasts only about four weeks. In our small backyard pond, though, I watched this process last for at least eight weeks. After about eight weeks of gleaning small amounts of algae, many of them were “sprouting” tiny back legs, I noticed. Still, for another week or more, these now three-quarter-inch tadpoles with tails and back feet continued to feed on algae. Then, literally almost overnight, the tail started shortening and the head area began transforming to a similarly shaped head as the adult. In about 24 hours, the now shrinking tail was absorbed to supply them the needed energy needed to grow lungs, lose gills, sprout small front legs, change their gut from algae feeding to feeding on small invertebrates, and grow a wide mouth with a front attached tongue and grow small sharp teeth. And all of a sudden, they leave the pond. In fact, this transformation happened so quickly that my decision to wait one more day to photograph the final shape made me miss their dispersal from the pond. Of the thousands of eggs laid in April, I would estimate that about 50 to 60 tadpoles survived to the stage where they could transform into terrestrial amphibians. The time frame for the final part of their metamorphosis was amazing. In less than two days the pond where the tadpoles with hind legs and tails were feeding on algae was now missing the tiny three-quarter-inch toads that scattered somewhere in my or my neighbors’ yards. The transformation doesn’t end there. The thin, moist skin of the emerging toad quickly changes to a dry, warty skin. The toad still seeks out a daytime place to hide from the hot sun, emerging mostly at dusk to feed on insects, slugs or even earthworms. Test Your Outdoor Knowledge: True/False — Bullfrog tadpoles take a year until ready to lose their gills and finish metamorphosis. Last Week’s Trivia Answer: Blackpoll warblers, most nesting well to our north, will soon begin their long migration to areas in and around Argentina. Email Barry Reed at [email protected]