Meeting Abstract
The temperature constraint hypothesis suggests that herbivorous fish species are depauperate at higher latitudes because of a temperature constraint on digestive biochemistry. However, some herbivorous and omnivorous fishes, like Xiphister mucosus (herbivore) and Xiphister atropurpureus (omnivore), extend to the Aleutian Islands (52° N latitude), and can digest algal compounds at lower temperatures. We compared the activities of six different digestive enzymes in both species of Xiphister, as well as in the carnivorous, Anoplarchus purpurescens, collected from California (35° N latitude) and Washington (48° N latitude). Enzyme activities were measured at 15°C (California), and 10°C (Washington), which reflect the summer temperatures of each locale. Few differences in activity levels were observed. Because amylase digests algal starches, these findings suggest potential biochemical adaptation of amylases toward temperature. We, therefore, examined the electrophoretic patterns of amylases, only finding different allelic patterns in carnivorous A. purpurescens from CA and WA. Amylase genetic sequences were identical in X. mucosus collected from both locations, further supporting the lack of variation in amylases in these species. Therefore, despite different ambient temperatures, Xiphister species are able to digest algal starches without different amylase isoforms suited for different temperatures and may achieve elevated activities under cooler conditions by increased expression levels of amylase genes.