Male Silverstripe Shiners Have Bigger Brains, Too

Alexandra has been analyzing her examination and measurements of silverstripe shiner (Notropis stilbius) brains a bunch of different ways. In short, the results are similar to those for the related telescope and scarlet shiners: the males have bigger brains by relative volume than females. We're still working on the exact presentation of this data, but it's the missing piece for our NeuroReport article. Now we have western blot data on NMDAR for all three species, and brain size measurements to go with that. What we can say is that adult male breeding condition shiners have larger brains than females, and also have higher average NMDAR levels in their brain. But sexually dimorphic male scarlet shiners have higher NMDAR levels that are statistically significant. This implies that developing strong sexual dimorphism involves some subtle but fundamental brain reorganization.

I'll admit that for the moment I'm not entirely certain what it might mean that male shiners have larger brains than females. This relationship is also true for individual parts of the brain such as the optic tectum, cerebellum and telencephalon. It's not for being "smarter", but it could have something to do with processing environmental and/or social information. That's still a very large subject, with a very large handwave!