Tropical parabiotic ants: Highly unusual cuticular substances and low interspecific discrimination

<p>Abstract</p> <p>Background</p> <p>Associations between animal species require that at least one of the species recognizes its partner. Parabioses are associations of two ant species which co-inhabit the same nest. Ants usually possess an elaborate nestmate recognition system, which is based on cuticular hydrocarbons and allows them to distinguish nestmates from non-nestmates through quantitative or qualitative differences in the hydrocarbon composition. Hence, living in a parabiotic association probably necessitates changes of the nestmate recognition system in both species, since heterospecific ants have to be accepted as nestmates.</p> <p>Results</p> <p>In the present study we report highly unusual cuticular profiles in the parabiotic species <it>Crematogaster modiglianii </it>and <it>Camponotus rufifemur </it>from the tropical rainforest of Borneo. The cuticle of both species is covered by a set of steroids, which are highly unusual surface compounds. They also occur in the Dufour gland of <it>Crematogaster modiglianii </it>in high quantities. The composition of these steroids differed between colonies but was highly similar among the two species of a parabiotic nest. In contrast, hydrocarbon composition of <it>Cr. modiglianii </it>and <it>Ca. rufifemur </it>differed strongly and only overlapped in three regularly occurring and three trace compounds. The hydrocarbon profile of <it>Camponotus rufifemur </it>consisted almost exclusively of methyl-branched alkenes of unusually high chain lengths (up to C₄₉). This species occurred in two sympatric, chemically distinct varieties with almost no hydrocarbons in common. <it>Cr. modiglianii </it>discriminated between these two varieties. It only tolerated workers of the <it>Ca. rufifemur </it>variety it was associated with, but attacked the respective others. However, <it>Cr. modiglianii </it>did not distinguish its own <it>Ca. rufifemur </it>partner from allocolonial <it>Ca. rufifemur </it>workers of the same variety.</p> <p>Conclusion</p> <p>We conclude that there is a mutual substance transfer between <it>Cr. modiglianii </it>and <it>Ca. rufifemur</it>. <it>Ca. rufifemur </it>actively or passively acquires cuticular steroids from its <it>Cr. modiglianii </it>partner, while the latter acquires at least two cuticular hydrocarbons from <it>Ca. rufifemur</it>. The cuticular substances of both species are highly unusual regarding both substance classes and chain lengths, which may cause the apparent inability of <it>Cr. modiglianii </it>to discriminate <it>Ca. rufifemur </it>nestmates from allocolonial <it>Ca. rufifemur </it>workers of the same chemical variety.</p>

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