White-gutted soldiers: simplification of the digestive tube for a non-particulate diet in higher Old World termites (Isoptera: Termitidae)

R H Scheffrahn,J Šobotnik,C Bordereau,P Dieguez,V M Oelze,R A Hernandez-Aguilar,T Bourguignon,A Pascual-Garrido

doi:10.1007/s00040-017-0572-9

Abstract

Previous observations have noted that in some species of higher termites the soldier caste lacks pigmented particles in its gut and, instead, is fed worker saliva that imparts a whitish coloration to the abdomen. In order to investigate the occurrence of this trait more thoroughly, we surveyed a broad diversity of termite specimens and taxonomic descriptions from the Old World subfamilies Apicotermitinae, Cubitermitinae, Foraminitermitinae, Macrotermitinae, and Termitinae. We identified 38 genera that have this “white-gutted” soldier (WGS) trait. No termite soldiers from the New World were found to possess a WGS caste. Externally, the WGS is characterized by a uniformly pale abdomen, hyaline gut, and proportionally smaller body-to-head volume ratio compared with their “dark-gutted” soldier (DGS) counterparts found in most termitid genera. The WGS is a fully formed soldier that, unlike soldiers in other higher termite taxa, has a small, narrow, and decompartmentalized digestive tube that lacks particulate food contents. The presumed saliva-nourished WGS have various forms of simplified gut morphologies that have evolved at least six times within the higher termites.

Highlights

Trophallaxis is the mouth-to-mouth or anus-tomouth exchange of alimentary contents between members of a social insect colony (Wilson 1971)
In order to investigate the occurrence of this trait more thoroughly, we surveyed a broad diversity of termite specimens and taxonomic descriptions from the Old World subfamilies Apicotermitinae, Cubitermitinae, Foraminitermitinae, Macrotermitinae, and Termitinae
We show that Old World termitid soldiers can be sorted into two groups: the ‘‘white-gutted’’ soldier group (WGS) and the more common ‘‘dark-gutted’’ soldier group (DGS)

Summary

Introduction

Trophallaxis is the mouth-to-mouth (stomodeal) or anus-tomouth (proctodeal) exchange of alimentary contents between members of a social insect colony (Wilson 1971). In the lower wood-feeding termites (e.g., Kalotermitidae and Rhinotermitidae), soldiers are fed with worker gut contents which consist of mixtures of masticated wood particles and saliva (Grasse 1982; Noirot 1969). The diets of most higher termites (Termitidae) are much more varied (Donovan et al 2001), and soldiers are nourished by stomodeal trophallaxis with particles of worker-masticated wood, leaf litter, soil, fungus, bacteria, herbaceous plants, lichens, algae, or some derivation of these (e.g., sound vs severely decayed wood). (Sleaford et al 1996; Donovan et al 2001; Donovan 2002) which are transferred to their soldiers These particulate suspensions impart a contrastingly darker coloration to the gut tubes of both mature workers and soldiers, which are visible through their opaque or nearly transparent integument

Methods

Results

Conclusion