An influential scientist once told me that much of biology can be basically boiled down to poop and sex. In pursuit of the former, I found myself over the weekend at Fort Ord, a University of California Natural Reserve in Marina. Fort Ord protects a live oak forest and adjacent sandmat manzanita chaparral. The objective of the trip was to study the scats of medium-sized carnivores, such as coyotes, bobcats, and foxes. This is a central component of my wife’s doctoral research. As with most scatologically-oriented researches, her project is designed to learn about who eats whom in nature.
A related topic is how different animals try to keep themselves from being eaten. In late afternoon near the entrance to Fort Ord, Rachel and I saw a raven cornering an alligator lizard against the concrete curb at the edge of the road. The raven danced around the lizard, which stood with its back against the wall and its mouth open aggressively, staring death in the face. After a short tussle, the raven took off with a large piece of lizard meat writhing in its talons. The rest of the lizard skittered away into the chaparral, stunned but alive.
What we witnessed was the lizard’s self-amputation of its own tail. This predation-avoidance tactic is called autotomy; the idea is that if you’re a lizard under attack, you drop your tail as a distraction to the predator. The tail continues to flop around as though it were still alive, and meanwhile you make a break for the nearest cover. (If you don’t believe that it works, take a look at this youtube video.)
Lizards and skinks are frequently associated with autotomy, but a variety of other animals also employ this strategy. Known autotomizers include slugs (though not our local bananas), spiders, molluscs (including octopi), crustaceans, and bees. In the case of spiders, the appendages cast off are legs rather than tails, and the function may be to prevent envenomation (by wasps, for instance) rather than to avoid predation. Not surprisingly perhaps, research in arachnid autotomy has found that spiders are more likely to discard legs when a researcher injects “painful” substances into them rather than non-painful ones.
In bees, the discarded appendage does not have seven replicates to fall back on; during copulation, male honeybees turn their entire reproductive tract inside out and leave their genitalia inside of the queen.