Trypsin Gene Expression by Quantitative In Situ Hybridization in Carnivorous and Herbivorous Prickleback Fishes (Teleostei: Stichaeidae): Ontogenetic, Dietary, and Phylogenetic Effects

Abstract

We determined trypsin gene sequences and compared relative levels of trypsin gene expression as influenced by ontogeny, diet, and phylogeny in four related prickleback fish species. Of these species, Cebidichthys violaceus and Xiphister mucosus shift from carnivory to herbivory at approximately 45 mm standard length [SL], whereas Xiphister atropurpureus and Anoplarchus purpurescens remain carnivores. Pairwise sequence similarities among the four species were 77%-95% for the trypsin nucleotides and 69%-94% for the amino acids. Trypsin gene expression levels in small (30-40 mm SL) and larger (60-75 mm) wild-caught juveniles and larger (60-75 mm) juveniles raised on a high-protein artificial diet increased with ontogeny in all four species but in response to the diet only in the two carnivores. The indistinguishable expression levels in the sister taxa, X. mucosus and X. atropurpureus, represented the only apparent phylogenetic effect. Xiphister atropurpureus, however, increased both trypsin gene expression and enzymatic activity (the latter from a previous study) on the high-protein artificial diet, indicating transcriptional rather than posttranscriptional (shown in X. mucosus) regulation of the activity. This study provides evidence for genetically programmed upregulation of trypsin gene expression with ontogeny in both the carnivorous and herbivorous species but in response to the high-protein artificial diet only in the carnivores.