Eat ‘til you can’t eat no more: Evolution of the pig-out

Eating food is a wonderful activity. Without it, you’d die.

But have you ever gone overboard? Got to the end of a meal and thought:

“I ate too much.”

In the natural world, we’re so used to thinking of food as scarce for animals that we don’t often think about issues associated with animals that eat and eat and eat until they do not eat any more. It is probably fairly hard to hit that satiation point for many species.

On the other hand, some species are well known for infrequent but huge meals. They have to eat as much as they can when they can, because their food source is unpredictable. But how do you get to the ability to eat those large meals? We know the “I ate too much” sensation can be uncomfortable, but could it be costly in evolutionary terms?

Pruitt and Krauel decided to look at these issues of gorging in wolf spiders (Schizocosa ocreata). They collected many young female spiders in Tennessee, and reared them in the lab. To test how much the females could eat in one go, they fed them crickets.

A lot of crickets.

After the spiders were not taking any more crickets, they measured just how much mass the females had taken on in all that feeding. The females varied quite a bit in how much food they could take on, and there is a clear advantage to doing so: their eggs developed faster and they had more of them.

As I alluded to before, Pruitt and Krauel mated their females. They took the offspring and measure how gluttonous they were compared to their mother, and it turns out that the winners of the eating contest tended to have daughters who could also wolf down a lot of food, too. Eating large meals is heritable.

Now we get to the coolest part.

The researcher took those spiders into the wild, and let them loose.

But they didn’t just turn them loose because the experiment was done, oh no. They let them out in to locations in the Tennessee forest. One was covered with nets so that birds – likely the major predators of these spiders – were unlikely to be able to get in.

All their released spiders were marked so they could be identified. Every day for two weeks, they tried to recapture the spiders they released.

When it was all over, they estimated that their eating champions were more likely to survive and have reproductive success... but only in environments where the predators had been excluded. In the more naturalistic settings, where birds were free to zip down and conduct their own experiments in how much birds can eat, the heavy eaters suffered: they more likely to have been picked out of the population.

And the moral of the story is: Life is all about trade-offs. Sure, you can take in a lot of energy in one go... that will make you so slow that you can’t escape when you need to.

Swings and roundabouts, as they say.

This post is part of the National Evolutionary Synthesis Center (NESCent) competition for the Science Online 2011 conference.

Reference

Pruitt JN, & Krauel JJ. 2010. The adaptive value of gluttony: predators mediate the life history trade-offs of satiation threshold. Journal of Evolutionary Biology. DOI: 10.1111/j.1420-9101.2010.02070.x

Top photo by robstephaustralia on Flickr; bottom photo by dishevld on Flickr; used under a Creative Commons license.