01 December 2014

Build your brain by losing that gut

The old joke goes that places with terrible weather are made that way so only the best people live there. Dullards can’t hack it.

This little guy shows there may be some truth to that.

This is a black-capped chickadee (Poecile atricapillus). It’s a small bird that ranges over much of North America. Because it has such a wide distribution, the birds that live in different areas are slightly different from those that live in other areas. A recent paper by Kozlovsky and colleagues takes advantage of that to test an idea about brain size.

The expensive tissue hypothesis is an idea that says if you have more of one kind of expensive tissue (like brains), you will either have to:

  • Increase your overall metabolic rate to pay for the extra tissue.
  • Give up something. The original paper suggested that the gut was a prime candidate for reduction when brain size went up. It was also expensive, and you could compensate for a small digestive system with higher quality food.

A few papers have tested this, but this one is nice because it is all a single species. Kozlovsky and colleagues show nicely that the bigger the brain in the chickadee, the smaller the stomach and gut. This cleanly fits the expensive tissue hypothesis.

Heart size, on the other hand, does not correlate with brain size in any way. Again, this fits the original formulation of the expensive tissue hypothesis,  which predicted that heart muscle would be unaffected by brain size. The need to pump blood kind of limits how much you can reduce heart tissue.

What was a little less expected was the influence the climate had on the birds.

The birds living in cold climates, like Fairbanks, Alaska (pictured) had bigger brains, and smaller bodies, than those living in more moderate, easy-going climes. Either one might be easy to explain on its own, but the combination is unexpected. Usually, both body size and brain size go up hand in hand (or, in this case, wing in wing). It’s not entirely clear how this is happening, although it certainly suggests there are some strong weather-related selection pressures shaping both features.

One factor that might be coming into play is that chickadees are food caching birds, and cold weather may actually allow the northern chickadees to store higher quality food for longer. The Alaskan chickadees live in a deep freeze, as it were, that lets them store insects and such for longer, because the cold weather means they don’t rot.

Just when I was finishing this blog post, I saw this tweet:

Completing a PhD requires brains, guts, perseverance(.)

But... but... if you have more brains, you can’t have as much guts! It reminded me of another old joke: “Good. Fast. Cheap. Pick two.”


Kozlovsky DY, Branch CL, Roth II, TC, Pravosudov VV. 2014. Chickadees with bigger brains have smaller digestive tracts: a multipopulation comparison. Brain, Behavior and Evolution 84: 172-180. DOI: http://dx.doi.org/10.1159/000363686

Bird photo by Rick Leche on Flickr; winter picture by Curt on Flickr; both used under a Creative Commons license.

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