GAWLICKA, A.; HORN, M.H.; California State Univ., Fullerton; California State Univ., Fullerton: Gene expression of trypsin by in situ hybridization in carnivorous and herbivorous prickleback fishes (Stichaeidae): ontogenetic, dietary, and phylogenetic effects

We measured intensity of trypsin gene expression in four species of carnivorous and herbivorous stichaeid fishes and determined the effects of ontogeny, diet, and phylogeny on this intensity. Of the four species, Cebidichthys violaceus and Xiphister mucosus shift to a more herbivorous diet as they grow (>45 mm SL), whereas X. atropurpureus and Anoplarchus purpurescens remain carnivores throughout life. Gene expression of this protease in the four species was determined using in situ hybridization with an RNA probe and the intensity of expression quantified using image analysis. Intensity was compared in three feeding categories of the four species: (1) small, wild-caught juveniles representing the carnivorous condition before two of the species shift to herbivory; (2) larger, wild-caught carnivorous juveniles representing the natural diet condition of the two carnivorous species and the two that have shifted to herbivory; and (3) larger lab-fed juveniles produced by feeding a high-protein animal diet to small juveniles until they reached the size of the larger wild-caught juveniles. Comparisons of intensity in categories (1) vs. (2) allowed us to test for an ontogenetic effect, in (2) vs. (3) for a dietary effect, and within categories (1) and (2) for a phylogenetic effect. Our results showed a significant ontogenetic effect in only two species: A. purpurescens, as expected, and C. violaceus, not as expected; a significant dietary effect only in X. atropurpureus and that resulting in a decrease not an increase in expression; and a significant, and expected, phylogenetic effect only in that the sister taxa, X. atropurpureus and X. mucosus, were indistinguishable in trypsin expression intensity in all comparisons.