Tolerance Requires the Right Smell: First Evidence for Interspecific Selection on Chemical Recognition Cues

Abstract

The integument of insects is generally covered with cuticular hydrocarbons (CHC). They serve multiple functions, most prominent among them waterproofing and-especially among social insects-as communication signal. CHC profiles are incredibly diverse within and across species. However, the causes for CHC variation between species, and potential selection pressures that may shape CHC profiles, are hardly understood. Here, we investigated potential selection pressures on ant CHC. We tested the hypotheses that living in association with another species (e.g., parabiosis), and the climate of the ant's habitat, affect CHC composition. We conducted a large-scale comparison of 37 Camponotus species from five continents. Our results demonstrate that closely associated ant species possess significantly longer hydrocarbons and higher proportions of methylbranched alkenes and alkadienes than nonor loosely associated species. In contrast, climatic factors had no effects. This study shows that the need to be tolerated by another species greatly affects CHC profiles. K E Y W O R D S :Communication signals, cuticular hydrocarbons, evolution, Formicidae, interspecific interactions, selection pressure.

How do cuticular hydrocarbons evolve? Physiological constraints and climatic and biotic selection pressures act on a complex functional trait

“…in a previous study [42] are similar in Crematogaster species. The abundance of each substance class and the median chain length were each tested in linear mixed-effects models as described above.…”

“…This was known for Camponotus s.l. [42], but here we showed convergent effects in Crematogaster. Interestingly, the few differences we found between the two taxa mostly concern methyl-branched alkenes and the effects of parabiotic lifestyle.…”

“…For the sake of simplicity, we will use the term 'species' for the 85 taxa henceforth. A part of these samples have been used for different analyses in [42].…”

The influence of slavemaking lifestyle, caste and sex on chemical profiles in Temnothorax ants: insights into the evolution of cuticular hydrocarbons

“…This hypothesis is corroborated by the correspondence of relative n-alkane abundance and average chain-length in the different castes and species ( figure 2a,b). The shorter chain-lengths contrast with the extremely long ones (more than C40) reported for mutualistically associated parabiotic ants [57] and, partly, in an incipient leaf-cutting ant social parasite ( [62], but see [46]), whose profiles are characterized by longer-chained CHCs than non-associated species. Longer chain-length may lead to lower detectability of the CHC profiles, and hence hamper recognition [57,74].…”

“…Rather, similar selection pressures to avoid host recognition have probably led to convergent evolution of chemical traits in slavemakers. To the best of our knowledge, such general strategies that are similar across multiple interaction systems, and yield similar effects on CHC composition across species, have only been shown in mutualistic associations so far [57]. Myrmecophiles and social parasites frequently use chemical mimicry to overcome their hosts' recognition system [32].…”