Abstract
BackgroundAssociations 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.ResultsIn the present study we report highly unusual cuticular profiles in the parabiotic species Crematogaster modiglianii and Camponotus rufifemur 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 Crematogaster modiglianii 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 Cr. modiglianii and Ca. rufifemur differed strongly and only overlapped in three regularly occurring and three trace compounds. The hydrocarbon profile of Camponotus rufifemur 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. Cr. modiglianii discriminated between these two varieties. It only tolerated workers of the Ca. rufifemur variety it was associated with, but attacked the respective others. However, Cr. modiglianii did not distinguish its own Ca. rufifemur partner from allocolonial Ca. rufifemur workers of the same variety.ConclusionWe conclude that there is a mutual substance transfer between Cr. modiglianii and Ca. rufifemur. Ca. rufifemur actively or passively acquires cuticular steroids from its Cr. modiglianii partner, while the latter acquires at least two cuticular hydrocarbons from Ca. rufifemur. The cuticular substances of both species are highly unusual regarding both substance classes and chain lengths, which may cause the apparent inability of Cr. modiglianii to discriminate Ca. rufifemur nestmates from allocolonial Ca. rufifemur workers of the same chemical variety.
Highlights
Associations between animal species require that at least one of the species recognizes its partner
Ca. rufifemur actively or passively acquires cuticular steroids from its Cr. modiglianii partner, while the latter acquires at least two cuticular hydrocarbons from Ca. rufifemur
The cuticular substances of both species are highly unusual regarding both substance classes and chain lengths, which may cause the apparent inability of Cr. modiglianii to discriminate Ca. rufifemur nestmates from allocolonial Ca. rufifemur workers of the same chemical variety
Summary
Associations between animal species require that at least one of the species recognizes its partner. One of the closest and most intriguing interspecific associations is parabioses, where two ant species live together in a common nest This phenomenon is found in several parts of the world, including Southeast Asia [2] and tropical South America [3]. Parabiotic ants have nestmates from their own colony, and from a completely different species Their nestmate recognition system needs to include allospecific nestmates. The individuals continually take up their nestmates' surface compounds into the postpharyngeal gland (PPG), where they are mixed and redistributed Through this process, a colony-specific odour is created [5,9,10,11]. Nestmates are recognized by comparing the cuticular profile of the encountered individual to the neuronal template (phenotype matching), whereby a mismatch generally results in aggression [5]
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