Differences in cellulose digestive systems among castes in two termite lineages

Abstract

Abstract Termites (Isoptera) are eusocial insects and express polyphenism. Soldiers have specialized morphology for colony defense, but their feeding activity is dependent on other colony members. To determine differences in cellulose degradation between soldier and worker termites, enzymatic activity and cellulase gene expression, as well digestive tract histology, are examined in two phylogenetically distant species. In Hodotermopsis sjostesti (family Termopsidae) , endo‐β‐1,4‐glucanase activity is identified in the salivary glands, whereas β‐glucosidase activity is identified in salivary glands and hindgut. The relative expression levels of endo‐β‐1,4‐glucanase genes in soldiers are significantly lower than in workers. Thin sections of salivary gland of workers and soldiers are different in H. sjostedti . In Nasutitermes takasagoensis (family Termitidae), the endo‐β‐1,4‐glucanase activity is restricted to the midgut in four tested castes (i.e. three types of workers and soldier). Examination of activity per termite reveals the highest activity in minor workers and the lowest activity in major workers and soldiers. The β‐glucosidase activity is also concentrated on the midgut in all four castes. The relative expression level of the endo‐β‐1,4‐glucanase gene does not correspond with its activity in the midgut. In thin sections prepared from N. takasagoensis , the folds and pulvillus in the gizzards, and cuticle structure of soldiers are less developed compared with the other three worker castes. The differences in digestive system among termite castes in terms of caste development in each species are discussed.