Meeting Abstract

98.4  Monday, Jan. 6 14:15  Elevated amylase activities have different genetic underpinnings in prickleback fishes with different diets GERMAN, D.P.*; FOTI, D.M.; LOCKWOOD, B.L.; Univ. of California, Irvine; Univ. of California, Irvine; Univ. of Indiana dgerman@uci.edu

Many herbivorous vertebrates have elevated activities of the starch-degrading enzyme amylase in their digestive tracts, and this can arise by increased expression of a few genes, or increased amylase gene copy number. In this project, we compared amylase gene sequences, sequence variants, and amylase biochemistry in prickleback fishes (family Stichaeidae) with different diets to better understand the underpinnings of dietary amylase activity variation. The herbivorous fish Cebidichthys violaceus expresses at least two amylase isoforms (and likely three or more) that have 14 missense mutations among them. These two main C. violaceus isoforms have different isoelectric points (7.68 vs. 8.62), and structural differences that could affect function. Xiphister mucosus (herbivore) X. atropurpureus (omnivore), Phytichthys chirus (omnivore), and the carnivorous Anoplarchus purpurescens each appear to express a single amylase isoform. Thus, the elevated amylase activity in the species of Xiphister is largely explained by elevated expression of one gene. The herbivorous C. violaceus and X. mucosus evolved their dietary habits and elevated amylase activities independently, however, despite their genetic differences assays on crude gut homogenates suggest that both herbivores digest different starches with similar efficiencies. These data have implications for the digestion of different algal starches, as green algae use amylose and red algae use amylopectin as their storage polysaccharides, respectively. Therefore, convergent evolution of herbivory in C. violaceus and X. mucosus has different genetic underpinnings, but any functional consequences of these differences remain to be revealed.