Evolutionary considerations of the spatial organization of digestion in the luminescent predaceous larvae of Pyrearinus termitilluminans (Coleoptera:Elateridae)

Abstract

Amylase, cellulase, β-glucosidase and trypsin are found in major amounts in the midgut lumen and in regurgitated material, whereas aminopeptidase, α-glucosidase and trehalase occur mainly in the midgut tissue of Pyrearinus termitilluminans larvae. About 40% of the cell bound enzymes are membrane associated. Feeding seems to increase the luminal more than the cell-bound digestive enzymes. There is only one molecular species each of soluble aminopeptidase ( M r 118,000), amylase ( M r 64,000), cellulase ( M r 58,000), α-glucosidase ( M r 79,000), β-glucosidase ( M r 110,000) and trehalase ( M r 110,000) in P. termitilluminans midgut as judged by electrophoretic, isoelectric focusing and density-gradient centrifugation data. There are three trypsin activities resolved by electrophoresis and isoelectric focusing, and only one by centrifugation ( M r 39,000), suggesting that trypsin occurs as charged isomers. The pH optima of the digestive enzymes lie between 6 and 8.5, which agrees with the pH (7.3) value of the midgut contents. The data suggest that P. termitilluminans larvae regurgitate onto their prey their midgut contents which accomplishes initial digestion. Pre-liquefied material is then ingested by larvae and the intermediate and final digestion take place on the surface of the midgut cells. The adaptive features of the digestion of the P. termitilluminans larvae are thought to be derived characters evolved from a putative holometabolous vegetarian ancestor.