We start small and we get bigger. That’s the way it works for almost all life, and all vertebrates – except one. The marine iguana, found in the Galapagos, can literally shrink itself down when times get tough.


Life on an island can be difficult. Sure, islands provide a haven from predators, but when things go bad, island animals don’t have many options. They adapt to the bad conditions, or they die. In the Galapagos, things get tough regularly, whenever the El Niño phenomenon kicks in. For the marine iguanas, El Niño years can kill up to 90% of the population. The change in water temperature kills off the red and green algae that they typically live on, and promotes the growth of brown algae, which they can barely digest. Not every El Niño year is bad, but every year starves off a few of these iguanas.

The largest iguanas are the first to die, because large bodies require energy. Large grazers like these iguanas seem to be much worse at foraging for food than smaller grazers of the same species. To survive the starvation, these iguanas manage to do something that no other vertebrate can do — they shrink. They can lose up to 20% of their size, and what they’re losing isn’t fat. They’re losing bone mass. Their skeletons are getting smaller. Imagine a friend going on a diet and losing a foot in height.


What’s even more remarkable is the fact that, when food becomes plentiful again, and the iguana can eat its fill, it bulks back up. For most species, damage that deteriorates bone is very tough to heal. An iguana can shrink and grow, shrink and grow, again and again throughout its lifetime.

[Source: Marine Iguanas Shrink To Survive El Nino]