Telescope And Scarlet Shiner Brains Are Different?

Here's the summary of what we found last week with our western blots to compare levels of the brain protein NMDA in telescope shiners who aren't strongly sexually dimorphic (the first group below, NTF) and scarlet shiners who are strongly sexually dimorphic (the second group, LFF). The Pixels column shows the relative density of antibodies sticking to an NMDA subunit on the final western blot; the more NMDA, the more antibodies, the higher the number of pixels in a scan of the western blot sheet. Both groups are ordered in rank from lowest to highest pixel count, with an individual's GSI (gonadosomatic index, relative size of gonads) and most importantly, sex.

Fish Pixels GSI  Sex
NTF4 83790 3.3    F
NTF5 87593 5.1    F
NTF6 89159 3.4    M
NTF7 95164 7.6    F
NTF3 96783 6.2    F
NTF2 99341 10.4   F
NTF8 108922 1.5   M
NTF10 114232 8.2  F
NTF1 133115 3.1   M
NTF9 140939 11.3  F
   
Fish Pixels GSI Sex
LFF3 83610 24.0  F
LFF1 89193 4.2   F
LFF6 91365 5.4   F
LFF7 93240 10.1  F
LFF8 96498 8.3   F
LFF5 99356 7.1   F
LFF2 103807 1.4  M
LFF10 125540 3.1 M
LFF4 139951 1.8  M

The big news is that the three male scarlet shiners in our sample of nine scarlets have the highest pixel counts, i.e. the most NMDA present. The telescope shiners show no clear sex pattern, with the highest pixel individual being a female, and the three males scattered throughout the sample of ten individuals. Interestingly, both species have individuals in an almost identical pixel range of ~83,000 to ~140,000.

We have two possible conclusion about the scarlet shiner brains: either the NMDA content (and function) is more strongly shaped by an individual's sexual status than telescope shiner brains, or an individual's sexual status is shaped by NMDA content (and function). Remember, the NMDA receptors are necessary for learning and sexual activity, among other things. In this group of North American cyprinid fishes, brains may show phenotypic plasticity as well as more obvious phenotypic traits such as standard length and breeding coloration. We'd like to further confirm this relationship, for instance by examining the brains of a relative of the telescope shiner, the silverstripe shiner, which is also not markedly sexually dimorphic, and a relative of the scarlet shiner such as the pretty shiner. There may well be a phylogenetic component to this, it's still too early to make sweeping statements.