Cuticular hydrocarbon profiles differ between ant body parts: implications for communication and our understanding of CHC diffusion

Abstract

Insect cuticular hydrocarbons (CHCs) serve as communication signals and protect against desiccation. They form complex blends of up to 150 different compounds. Due to differences in molecular packing, CHC classes differ in melting point. Communication is especially important in social insects like ants, which use CHCs to communicate within the colony and to recognize nestmates. Nestmate recognition models often assume a homogenous colony odour, where CHCs are collected, mixed and re-distributed in the postpharyngeal gland (PPG). Via diffusion, recognition cues should evenly spread over the body surface. Hence, CHC composition should be similar across body parts and in the PPG. To test this, we compared CHC composition among whole-body extracts, PPG, legs, thorax and gaster, across 17 ant species from three genera. Quantitative CHC composition differed between body parts, with consistent patterns across species and CHC classes. Early-melting CHC classes were most abundant in the PPG. In contrast, whole body, gaster, thorax and legs had increasing proportions of CHC classes with higher melting points. Intra-individual CHC variation was highest for rather solid, late-melting CHC classes, suggesting that CHCs differ in their diffusion rates across the body surface. Our results show that body parts strongly differ in CHC composition, either being rich in rather solid, late-melting or rather liquid, early-melting CHCs. This implies that recognition cues are not homogenously present across the insect body. However, the unequal diffusion of different CHCs represents a biophysical mechanism that enables caste differences despite continuous CHC exchange among colony members.

Uncovering variation in social insect communication

“…While CHC variation between individuals has been widely documented ( Sprenger and Menzel 2020 ), the possibility that CHC blends might differ within the same individual has rarely received attention ( Bonavita-Cougourdan et al 1993 ; Wang et al 2016 ; Wang et al 2019 ). Sprenger et al (2021 ) now provide the first evidence that CHC variation among body parts is far from being an exception in ants. In their paper, the authors investigated the CHC composition of different body parts in 17 ant species from three different genera.…”

Three cuticular amides in the tripartite symbiosis of leafcutter ants

“…Although it is exhibited that ants have evolved unique exocrine glands, little is known about the transport of secretions over the ants' surface (Blomquist & Bagnères, 2010; Tranter et al, 2015). In contrast, there is proof that CHC levels differ on different body parts of the ants (Sprenger et al, 2021). This difference might explain why some body parts are stronger inhabited by microbiota than others (Poulsen et al, 2002, 2003).…”

Cuticular hydrocarbons of alpine bumble bees (Hymenoptera: Bombus) are species-specific, but show little evidence of elevation-related climate adaptation

“…CHC profiles were extracted from legs and wings of all workers, as these body parts were shown to have the highest volume to surface ratio and best reflect climate-associated chemical traits in ants (Sprenger et al, 2021) while being representative for a species and revealing individual differences at the same time (Young et al, 2000;Wang et al, 2016;Mayr et al, 2021;Sprenger et al, 2021). Extraction was performed by immersing pooled body parts in n-hexane for 10 min per individual.…”