Toward a More Comprehensive View of -Amylase across Decapods Crustaceans

Decapod crustaceans live in practically all marine, freshwater, and semi-terrestrial habitats on Earth, and exhibit a remarkable variation in their feeding behavior, from filter feeding, grazing, and scavenging to hunting. However, most knowledge about digestive biochemistry in crustaceans has come from studies on a few economically relevant species due to the importance of optimized formulated feeds for aquaculture success. Moreover, most data on alpha-amylases in decapods derived from studies in herbivore and omnivore species. There are few reviews addressing different aspects of the digestive physiology of decapods, including data on digestive enzymes, but no comprehensive review is available on alpha-amylases in this group and, in general, information on carnivorous species is often neglected. This review summarizes the information obtained on decapods' alpha-amylases and uses recent data from a carnivorous lobster as a connecting thread to compare features of alpha-amylases from species with different feeding habits, drawing a more comprehensive view of the role of alpha-amylases across decapods crustaceans. Decapod crustaceans are a very diverse group and have evolved to suit a wide variety of diets. Alpha-amylases enzymes, responsible for starch and glycogen digestion, have been more thoroughly studied in herbivore and omnivore than in carnivorous species. We used information on the alpha-amylase of a carnivorous lobster as a connecting thread to provide a more comprehensive view of alpha-amylases across decapods crustaceans. Omnivorous crustaceans such as shrimps, crabs, and crayfish present relatively high amylase activity with respect to carnivorous crustaceans. Yet, contradictory results have been obtained and relatively high activity in some carnivores has been suggested to be a remnant trait from ancestor species. Here, we provided information sustaining that high enzyme sequence and overall architecture conservation do not allow high changes in activity, and that differences among species may be more related to number of genes and isoforms, as well as transcriptional and secretion regulation. However, recent evolutionary analyses revealed that positive selection might have also occurred among distant lineages with feeding habits as a selection force. Some biochemical features of decapod alpha-amylases can be related with habitat or gut conditions, while less clear patterns are observed for other enzyme properties. Likewise, while molt cycle variations in alpha-amylase activity are rather similar among species, clear relationships between activity and diet shifts through development cannot be always observed. Regarding the adaptation of alpha-amylase to diet, juveniles seem to exhibit more flexibility than larvae, and it has been described variation in alpha-amylase activity or number of isoforms due to the source of carbohydrate and its level in diets, especially in omnivore species. In the carnivorous lobster, however, no influence of the type of carbohydrate could be observed. Moreover, lobsters were not able to fine-regulate alpha-amylase gene expression in spite of large changes in carbohydrate content of diet, while retaining some capacity to adapt alpha-amylase activity to very low carbohydrate content in the diets. In this review, we raised arguments for the need of more studies on the alpha-amylases of less studied decapods groups, including carnivorous species which rely more on dietary protein and lipids, to broaden our view of alpha-amylase in decapods crustaceans.