Posted by zen woods on December 9, 2007

Q: When the sea iguana of the Galapagos Islands is in danger, as when a shark approaches, it completely changes colour and stops its heart, so the shark can't hear it. It seems that a shark can hear the heartbeat when it's three or four metres away, but its vision is very poor. Consequently, this strange adaptation makes good sense. Apparently though, one other animal can voluntarily stop its own heart ñ the komodo dragon. In this case, the komodo is pretty much the top predator in its natural habitat, so under what circumstances would it need to be able to stop its heart?

State: Outside the U.S. and Canada

A: >

> Thanks for your interesting question Zen. I've never heard about this phenomenon in these two animals and wonder where you heard about it. I must admit, I'm rather skeptical. I think your question about the Komodo Dragon, if it's true, is an excellent one however - I just don't think this is the case for either animal.

When the Galapagos Iguana dives for food in the ocean, it withdraws blood from its peripheral areas to conserve as much body heat as it can. Furthermore, it also dramatically reduces its heart rate to conserve its oxygen supply while underwater. I wonder if someone read this fact and assumed that they meant it's heart actually stopped? I can't imagine that any beating of their heart would be picked up by nearby sharks but then stranger things can and do occur in nature. The Komodo Dragon is an ectotherm also so I'm sure their heart rate does vary, especially in cool weather but I really doubt it ever stops. So...to the best of my knowledge, neither the Galapagos Iguana nor the Komodo Dragon actually stops its heart, they just slow them down. You can check out this website about the Galapagos Iguana and it remarks about the blood and heart rate effects.

www.rit.edu

Hope this helps. Thanks for asking.

John Wiessinger ( December 9, 2007)