Male Telescope Shiners Have Relatively Larger Brains

Yeah, it's true, based on examining telescope shiners we collected at Hurricane Creek in April and June last year. We have a sample size of about 20 for each month, 10 females and 10 males. What we've done is calculate brain weight as a fraction of somatic (body) weight, and graph that against standard length. So the graph below shows three interesting relationships. First, that males have a relatively larger brain at a given size, and second, that relative brain size decreases with increasing length, so that a very big (always female) telescope shiner has a brain that makes up about 1% of total body mass. So here's the graph. The males of both months each have a short line, because males only get so big, while the longer lines are females since they attain a significantly larger size than males (the opposite is true with scarlet shiners). And thirdly, notice that the linear regressions reported for males have very low R-squared values compared to the females. This means that relative male brain size is much more variable than that of females. This would be expected, since in any vertebrate species males have much more variable reproductive success because of variable phenotype. We haven't found any reference to anyone else observing such a relative brain size to body length relationship. (The image appears in a separate window if you click on it.)