Why do ants differ in acclimatory ability? Biophysical mechanisms behind cuticular hydrocarbon acclimation across species

Abstract

Maintaining water balance is vital for terrestrial organisms. Insects protect themselves against desiccation via cuticular hydrocarbons (CHCs). CHC layers are complex mixtures of solid and liquid hydrocarbons, with a surprisingly diverse composition across species. This variation may translate to differential phase behaviour, and hence varying waterproofing capacity. This is especially relevant when temperatures change, which requires acclimatory CHC changes to maintain waterproofing. Nevertheless, the physical consequences of CHC variation are still little understood. We studied acclimatory responses and their consequences for CHC composition, phase behaviour, and drought survival in three congeneric ant species. Colony fragments were kept under cool, warm, and fluctuating temperature regimes. Lasius niger and platythorax, both of which are rich in methyl-branched alkanes, showed largely predictable acclimatory changes of the CHC profile. In both species, warm acclimation increased drought resistance. Warm acclimation increased the proportion of solid compounds in L. niger but not in L. platythorax. In both species, the CHC layer formed a liquid matrix of constantly low viscosity, which contained highly viscous and solid parts. This phase heterogeneity may be adaptive, increasing robustness to temperature fluctuations. In L. brunneus, which is rich in unsaturated hydrocarbons, acclimatory CHC changes were less predictable, and warm acclimation did not enhance drought survival. The CHC layer was more homogenous, but matrix viscosity changed with acclimation. We showed that ant species use different physical mechanisms to enhance waterproofing during acclimation. Hence, the ability to acclimate, and thus climatic niche breadth, may strongly depend on species-specific CHC profile.

Indigenous and introduced Collembola differ in desiccation resistance but not its plasticity in response to temperature

“…Here we do so too. A response in desiccation resistance to temperature as a cue (and specifically temperature acclimation) alone has been demonstrated in hemiedaphic and other Collembola ( Chown et al., 2007 ; Leinaas et al., 2009 ; Phillips et al., 2020 ) and in insects ( Terblanche and Chown, 2006 ; Fischer and Kirste, 2018 ; Baumgart et al., 2022 ). Using temperature as a cue to elicit a response to dry conditions not only has these empirical precedents, but also has a firm basis in theory.…”

“…Such a system appears to be conserved across invertebrates ( Russell et al., 2014 ; Enjin, 2017 ). Moreover, at high temperatures more cuticular hydrocarbons (CHCs) melt and those that are liquid show a viscosity decline ( Baumgart et al., 2022 ). Therefore, a theoretical expectation exists and some empirical data support the idea that temperature change alone should elicit a desiccation resistance response.…”

Acclimation in ants: Interference of communication and waterproofing through cuticular hydrocarbons in a multifunctional trait

“…Second and more importantly, previous studies showed that acclimatory CHC changes are linked to drought resistance (Menzel et al, 2018). Also, for the ants studied here, warm acclimation significantly increased drought survival in both species compared to cold acclimation, with ants from the fluctuating treatment in between (Baumgart et al, in press). However, waterproofing not only requires solid or highly viscous compounds like n‐ alkanes and monomethyl alkanes.…”

“…Beside the lower effect sizes of acclimation in the PERMANOVA analyses, per cent changes between 20°C and 28°C treatments were much higher in L. platythorax than in L. niger . The lower acclimatory changes also affected fitness: the acclimatory increase in drought survival was substantially lower in L. niger than in L. platythorax (Baumgart et al, in press).…”

“…In this study, we investigated how information content, such as the colony signal, is maintained during acclimatory changes in the sister species Lasius niger and L. platythorax . Given that acclimatory CHC changes are linked to increases in survival in these and other ant species (Baumgart et al, in revision; Menzel et al, 2018), it is plausible that those CHCs that increase during warm acclimation are those responsible for waterproofing. We used different temperature regimes to induce acclimatory CHC adjustment to different waterproofing requirements and investigated how these changes affected information content.…”