Tuesday, July 7, 2009

Bat-Moth Echolocution Arms Race

One of the interesting aspects of evolution is the production of "arms races" between predator and prey, each adapting to counter the adaptions of the other. Gazelles get faster, so the cheetahs get even faster, and so on. Here's a great article on such an arms race involving the echolocation of bats and the counterevolution of the moths that are their prey:

Tiger moths have evolved the ability to produce ultrasonic clicks in response to attacking bats. However, the function of these clicks was unclear, although decades of research has led to a number of hypotheses. The clicks may act to startle attacking bats, or they may be an acoustic signal which warns them that the moth is unpalatable. A study published in today's issue of the journal Science provides the first clear evidence for the third hypothesis - that the clicks interfere with (or "jam") the bats' echolocation signals.

The analysis of their experiments revealed just how much detailed knowledge we have of bats:

Analysis of the film footage also revealed that the clicks led to unusual echolocating behaviour. Normally, a bat's attack progresses through three phases. First, it approaches its target. Then, it increases the frequency and amplitude of its echolocation signals; this so-called "feeding buzz" enables it to generate a more detailed auditory image, so that it can homes on and track the target. Finally, during the terminal phase of the attack, it captures its prey. Corcoran and his colleagues noticed that the ultrasonic clicks produced by the tiger moths led to atypical echolocation behaviour in the bats. In about one third of the attacks, the bats reversed the attack phase, from tracking to approaching, or from the terminal phase to tracking, before continuing with the attack.

It is important to keep items like this in mind any time someone makes an anti-scientific argument that amounts to "Here's something totally obvious and basic that they've overlooked" (eg "if we evolved from monkeys, then why are there still monkeys?"). Scientists are human with foibles and biases like anyone else. But they are also very intelligent, spend their lives studying their subjects, and don't all have the same biases. So there's nothing obvious and basic to a laymen that is going to be overlooked by the entire scientific enterprise. They've gone way beyond basic into arenas with questions that most of us are just too ignorant to ask.

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