One of the highlights of our trip to the U.S. last year. aside from visiting the science-blogging conference, was a trip to see the exhibits at the National Geographic Society museum in Washington, D.C. Our goal was their new Nigersaurus taqueti skeleton. It was an extra treat to find a whole exhibit of exotic frogs, including many terrariums holding live specimens.
This one is the Amazon milk frog. This one has a strategy for raising its young that illustrates that evolution preserves what works, not what we find fair. The frogs must lay their eggs in water. So the males stake out a tree with a water-filled hollow. They call and invite a female to come and lay her eggs. The male fertilizes the eggs by spreading his sperm-laden “milt” on top and they start to develop into tadpoles. The male watches over the eggs and calls another female. She, too, comes and lays her eggs. But this time the male doesn’t fertilize them. When the first eggs hatch, the young tadpoles eat the second batch of eggs. So a female that accepts a mate has only a 50% chance of having her eggs brooded to hatch.