Parallel recognition systems in parabiotic nests: no evidence for interspecific gestalt or interspecific nestmate reocognition

Background/Question/Methods

The great success of social colonies depends on recognition mechanisms to be able to exclude intruders and direct social benefits appropriately to colony members. Informational constraints on the signals used for these recognition processes has resulted in an incredible diversity of chemical phenotypes amongst the social insects. Social parasites have evolved multiple times to co-opt these recognition signals, but it is unknown whether a similar process occurs with nest-sharing mutualists. Parabiosis is a mutualistic relationship where two species sharing a nest, but is distinct from most social parasitisms in that brood are kept separate, and the species are not closely related. We investigated the recognition cues (cuticular hydrocarbons) and recognition behaviors in the parabiotic mixed-species ant nests of Camponotus femoratus and Crematogaster species to look for evidence of interspecific recognition. 

Results/Conclusions

Firstly, we were surprised to find two reproductively isolated Crematogaster chemotypes sharing nests with Ca. femoratus. We identified 68 cuticular hydrocarbons amongst the parabiotic species, with 4 compounds shared between Ca. femoratus and Cr. Type A, 9 with Cr. Type B, and only 2 compounds common to all three of the parabiotic ants. The Ca. femoratus hydrocarbons were mostly extremely long-chain methyl-branched alkenes. The lack of a mixed interspecies odor was consistent with an absence of interspecific nestmate or chemotype recognition. Although there was no evidence for interspecific recognition, each parabiotic species maintains its own recognition behaviors to exclude conspecific non-nestmates. This suggests that parabiotic ants maintain their own species-specific recognition cues and recognition mechanisms. The long-chain hydrocarbons of parabiotic Camponotus ants may allow coexistence not only because of their chemical insignificance, but perhaps also by allowing parallel chemical information to function within the parallel recognition systems in these multi-species nests. We propose these findings are evidence of informational character displacement unrelated to the commonly studied reproductive character displacement, and that informational constraints on non-sexual cues may lead to character displacement in other systems.