In a pond by the side of an Arizona highway, a group of spadefoot tadpoles have developed enlarged heads and protruding teeth. These tadpoles are specialized meat eaters who will compete with their fellow omnivorous tadpoles in a race for time. I’m Jim Metzner, and this is the Pulse of the Planet, presented by the American Museum of Natural History.
“The monsoon season is drawing to a close and so this pond is starting to dry out pretty rapidly. So these tadpoles are faced with dilemma.”
Tony Frankino is with the Biology Department at Indiana University. He tells us that the tadpoles have only a few weeks to complete their metamorphosis into spadefoot toads and to gain enough fat to last them through the winter.
“They need to stay in the water as long as they can, because the longer that they’re in the water, the bigger they’re going to be and the bigger they are, the better off they are when they come out. But, if they wait too long to metamorphose, then they’re not going to have legs and they’re going to run out of water and they’ll die in the desert sun. So, one strategy that these tadpoles have is to change from their standard tadpole like form, these omnivorous generalized tadpoles, they can change from that and become these carnivore specialists: they eat these shrimp that are in the pool and they eat other tadpoles”
But becoming a meat eater is a gamble. On the one hand, these carnivorous tadpoles will transform into toads at a faster rate, but your typical omnivorous tadpole will be better prepared for winter.
54:19 “Carnivores have lower fat reserves at metamorphosis and they have lower resistance to starvation than do the omnivores. And that’s important out here because tadpoles come out of the water, they need to put on as much fat as they can before they go underground for about ten months, to wait for next year’s rains.”
So, some years the meat eaters will do well while other years, depending upon the weather, the strategy of the omnivorous tadpoles will prevail.
Additional funding for Pulse of the Planet has been provided by the National Science Foundation. I’m Jim Metzner.