Cuticular hydrocarbons and collective response to water stress in a desert ant

Abstract

1. With the accelerating pace of climate change, we urgently need to understand how physiological traits shape behavioural plasticity in response to environmental stress. In social insects, collective behaviour operates without central control but through interactions among individual participants. In the aggregate, this produces a collective response to environmental conditions. 2. Here we consider how variation among desert ant colonies in the cuticular hydrocarbons (CHCs) that prevent water loss is associated with variation among colonies in the collective behaviour that manages water stress. Colonies of the desert ant, Pogonomyrmex barbatus, differ in the collective regulation of foraging activity to manage water loss to evaporation while foraging. Foraging is regulated through olfactory interactions between outgoing and returning foragers, which determine a forager's decision whether to leave the nest on the next trip. Some colonies are risk-averse, with foragers less likely to make foraging trips in dry conditions, while others are risk-tolerant, with foragers who do not reduce foraging trips in dry conditions. 3. We found that behavioural differences among colonies are associated with the capacity of their foragers' CHCs to prevent water loss. In risk-averse colonies whose foragers make fewer trips in dry conditions, the abundance of alkenes was significantly higher. High abundance of alkenes, with a low melting point, makes the CHC layer more permeable, increasing susceptibility to water loss. In one of 2 years of this study, we found that workers in risk-averse colonies also had significantly shorter n-alkanes, which further enhance water permeability of the CHC layer and thus desiccation risk. 4. To our knowledge, this is the first report of variation among conspecific colonies in CHC profile that is linked to colony differences in collective behaviour.