Males have bigger brains than females, if those males are sticklebacks from Iceland

This supershort paper contains an interesting fact: there is a population of male stickleback fish out there with big brains. The males fish that have brains 23% larger than the females of approximately equal size.

This is a bit of an unfair characterization. The paper does talk a little bit about how the look for differences in brain size according to the local eco-type that they found the fish and: mud or lava. the nails from allow the environments have bigger brains than those from muddy environments, but there is no such difference in the females.

This is an interesting difference, because so few animals have differences in brain size mispronounced between males and females. Kotrschal and colleagues say that this is the biggest difference in overall brain size in males and females to date.

What are we to make of this one interesting fact? The team speculates that this might be because the males make complicated nests, and compete for females through courtship displays. But it seems that there are many other animals that have similar differences in behavior without the differences in overall brain size. Maybe the real question is not why male brains are so big, but why are female brains in this fish so small? The authors speculate that this might be because the females are investing energy in egg production. Again, it doesn’t really answer why it should be so specifically strong in this particular population of this particular fish when all sorts of females invest energy in making eggs.

While the fact that this paper presents is interesting, a fact in isolation is mainly a curiosity, to borrow a phrase from psychologist Ernst Hilgard. I would’ve liked to have seen this fact presented slightly longer paper with a few more experiments and a little more context. There will surely be some interesting follow-up studies to do.

Reference

Kotrschal A, Räsänen K, Kristjánsson B, Senn M, Kolm N. 2012. Extreme sexual brain size dimorphism in sticklebacks: a consequence of the cognitive challenges of sex and parenting? PLoS ONE 7(1): e30055. DOI: 10.1371/journal.pone.0030055

Photo by Noel Burkhead on Flickr; used under a Creative Commons license.