Crop-gizzard content and volume variations among afrotropical Apicotermitinae (Blattodea, Termitidae)

Abstract

Termites are dominant organisms of tropical ecosystems. Their success is partly due to the diversity of their feeding substrates, from dead plant tissues to mineralised soils. The Apicotermitinae is one of the richest subfamilies of soil-feeding termites, which are traditionally classified in feeding groups according to anatomical criteria, deemed to the reveal whether species feed on organic-rich layers (group III) or on mineralised soil (group IV). Previous studies based on δ 15 N isotopic values showed that this subfamily's niche covers a broad range along the gradient of humification. We hypothesised that this broad feeding range could be reflected in the crop-gizzard (Cr-Gi) content and volume. We investigated 17 African species distributed between the two feeding groups. Our results showed a variation of Cr-Gi volume and a consistent composition of content among Apicotermitinae species. Some small-bodied species had a very large Cr-Gi volume relative to their size, indicating a difference in foraging behaviour. These species might use this enhanced storage capacity to forage for longer periods of time. Cr-Gi content was dominated by clay (kaolinite) suggesting that a dietary specialisation could be based on the quality of organic compounds from organo-mineral aggregates. Variations in crystalline solids (quartz) between species indicate either differences in the abundance of mineral grains between feeding patches or active discrimination among particles by foragers. The similar composition of Cr-Gi contents in afrotropical Apicotermitinae suggests that the anatomical criteria used to assign species to feeding groups III or IV are not appropriate.