Tadpoles are often used to teach students about the cycle of life as they go through a very visible metamorphosis, literally changing their form as they mature into frogs. Tadpoles can regrow their tails, a regenerative ability that makes them useful for scientific study. But some of this research raises some ethical qualms, including a recent experiment in which scientists implanted an eye from one tadpole into the tail of another.
Yes, that sounds at least like science fiction of the troubling kind. Tadpoles and frogs have long been used in scientific experiments. As they are vertebrates without an egg shell, their development can be readily observed from the embryo stage onward and some species are easily raised in captivity. They also reach reproductive age in just a few months, so studies across generations are possible in a short period of time.
Tadpoles Into Frogs
Born from clusters of a few to several hundred jelly-like eggs with gills like fish, some tadpoles become frogs in a few weeks, while others do so in months. Tadpoles at first consist mostly of a head and a tail. They eat voraciously — metamorphosis takes a lot of energy — and start to grow back legs (you can get an idea of the many varieties of tadpoles in the southeastern U.S. from this guide).
Tadpoles’ front legs are the next to form, along with changes in their internal organs: they acquire lungs so they can breathe air and their digestive systems change. While adult frogs are carnivores, tadpoles are omnivores who eat algae, rotting vegetation and (survival of the fittest) other tadpoles.
In the wild, frog eggs and tadpoles are themselves eaten by fish, birds and other animals; most tadpoles do not survive into adulthood. They have developed some adaptations to improve their chances, such as their flexible tail that, when caught by a predator, tears easily. In fact, a tadpole can still swim even when it loses as much as a quarter of its tail. Tadpoles can then regrow their tails and one study suggests that (especially when stressed by prolonged predator attacks), they grow larger tails.
Tadpole Eyes Implanted in Tadpole Tails
Implanting one tadpole’s eye into the tail of another takes this regenerative ability into quite another direction. In an experiment, scientists at Tufts University transplanted eyes from tadpole embryos onto the tails of other tadpoles who had been blinded. The tadpoles were found to be able to see from the eyes in their tails.
The purpose of this experiment is to see how well a “displaced eye” can see, to help scientists in developing software for robots (who would be able to “see” from many of their different parts) and also in creating prosthetic sensory organs (perhaps even an eye that could, indeed, help a person to see).
But now, in a lab at Tufts University, there are apparently frogs that have eyes on their derričres. It’s a “transformation” in the name of science and of creating new technologies to help us. But talk about a disruption of the usual development of tadpoles!
The natural metamorphosis that tadpoles undergo is one explanation for folktales of frogs being able to change their form, like that of the frog prince who becomes human after a princess kisses him. Eyes implanted on their hindquarters seems more like a horror story. Are some experiments, even if they’re intended ultimately to benefit humans’ health, going too far, altering what nature made in unnecessary ways?
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