How to Design Experiments in Animal Behaviour: 12. Male Frogs Sing for Sex but Why Dona??t They Do Their Best?

摘要

Charles Darwin proposed a separate theory of sexual selec-tion, as distinct from his theory of natural selection, to ac-count for adaptations that confer success in ???nding a mate, which may sometimes be quite the opposite of what is best for survival. Darwina??s proposal that females have a sense of beauty and choose mating partners that appear beautiful to them was met with much scepticism. But today we have a rather detailed understanding of what animals ???nd beauti-ful and why. In this article, I will describe a few very sim-ple experiments performed by Michael J. Ryan, in collabora-tion with A. Stanley Rand, herpetologist extraordinaire and Merlin D Tuttle of the Bat Conservation International fame, that laid the foundation for our current understanding of the meaning and evolution of beauty. Studying the t?′ungara frog on Barro Colorado Island, a research station of the Smithso-nian Tropical Research Institute in Panama, they showed that (1) male t?′ungara frogs can produce both simple calls, consist-ing of just a whine, or complex calls in which one or more chucks are added to the whine, (2) female t?′ungara frogs have a decided preference to mate with males giving complex calls,(3) males are nevertheless reluctant to add chucks to their calls and generally do so only when they hear other males calling, and (4) the local predatory fringe-lipped bat also has a decided preference to eat males giving complex calls. Male t?′ungara frogs thus face a trade-o??? between sex and survival. These experiments not only answered the question of why males dona??t do their best when it comes to singing, but they also set the stage for many more sophisticated investigations that have led to an understanding of how and why natural selection has favoured this particular sexual aesthetic in the frogs and this particular culinary aesthetic in the bats.