Intraspecific nestmate recognition in two parabiotic ant species: acquired recognition cues and low inter-colony discrimination
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Parabiotic ants—ants that share their nest with another ant species—need to tolerate not only conspecific nestmates, but also nestmates of a foreign species. The parabiotic ants Camponotus rufifemur and Crematogaster modiglianii display high interspecific tolerance, which exceeds their respective partner colony and extends to alien colonies of the partner species. The tolerance appears to be related to unusual cuticular substances in both species. Both species possess hydrocarbons of unusually high chain lengths. In addition, Cr. modiglianii carries high quantities of hereto unknown compounds on its cuticle. These unusual features of the cuticular profiles may affect nestmate recognition within both respective species as well. In the present study, we therefore examined inter-colony discrimination within the two parabiotic species in relation to chemical differentiation. Cr. modiglianii was highly aggressive against workers from alien conspecific colonies in experimental confrontations. In spite of high inter-colony variation in the unknown compounds, however, Cr. modiglianii failed to differentiate between intracolonial and allocolonial unknown compounds. Instead, the cuticular hydrocarbons functioned as recognition cues despite low variation across colonies. Moreover, inter-colony aggression within Cr. modiglianii was significantly influenced by the presence of two methylbranched alkenes acquired from its Ca. rufifemur partner. Ca. rufifemur occurs in two varieties (‘red’ and ‘black’) with almost no overlap in their cuticular hydrocarbons. Workers of this species showed low aggression against conspecifics from foreign colonies of the same variety, but attacked workers from the respective other variety. The low inter-colony discrimination within a variety may be related to low chemical differentiation between the colonies. Ca. rufifemur majors elicited significantly more inter-colony aggression than medium-sized workers. This may be explained by the density of recognition cues: majors carried significantly higher quantities of cuticular hydrocarbons per body surface.
KeywordsCamponotus rufifemur Crematogaster modiglianii Cuticular hydrocarbons Interspecific associations Nestmate recognition cues
We are grateful to Heike Feldhaar and Annett Endler for fruitful discussions and support in the GC-FID analysis. The Malaysian Economic Planning Unit (EPU) and the Danum Valley Management Committee (DVMC) kindly gave permission for our research, and Dr. Arthur Chung (Forest Research Center, Sepilok) functioned as our local collaborator. This study complies with current laws of Malaysia. F.M. was supported by a doctoral fellowship of the Bayerische Graduiertenförderung (BayEFG) and the Studienstiftung des deutschen Volkes. This work was also supported by the Sonderforschungsbereich SFB-554 ‘Mechanisms and Evolution of Arthropod Behaviour’ of the Deutsche Forschungsgemeinschaft (DFG).
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