More Fish Brain Data, Male vs Female, For Scarlet Shiners

Enrique and Leigh have now removed the brains from all of the scarlet shiners we had available from this summer's collections, for a grand total of 85. My arbitary goal had been 100, but this'll work. With this expanded data set, the trends that were apparent after only 45 were still there: male brain size is more variable than female brain size, as described by a linear regression of brain mass as a dependent variable against body mass as the independent variable. The R-squared for male brains is 0.29, the R-squared for females is 0.69. For your viewing pleasure I have posted the two graphs below. If you double click them you can view them so they're legible, I hope.
























Our next step is to measure the volume of three key brain areas in a representative sample of males and females so that we can try to explain the basis for the wider spread in male brain size. We'll be looking at the telencephalon, the optic tectum and the cerebellum, which are pretty much the three biggest regions in a scarlet shiner brain. The optic tectum in particular is large. This structure processes visual information which is important if you're a scarlet shiner living in a shallow pool of clear water, their preferred habitat. It's my bet (hypothesis, really) that this turns out to be the variable area, which would mean that some male fish have better vision than others. We'll see.