Selective interspecific tolerance in tropical Crematogaster–Camponotus associations

Associations between ants of the genera Crematogaster and Camponotus are found in many parts of the world. Associated species use common trails (trail sharing) or even share a common nest (parabiosis). In a tropical lowland forest in Malaysian Borneo, we studied intraspecific and interspecific aggression among the parabiotic species Crematogaster modiglianii and Camponotus rufifemur using both field and laboratory assays. Cr. modiglianii tolerated Ca. rufifemur workers from certain foreign colonies but fiercely attacked those of others. In contrast, Ca. rufifemur was tolerant even towards attacking allocolonial Cr. modiglianii workers but killed other Crematogaster species. By analogy, other Camponotus species usually attacked and killed Cr. modiglianii. Intraspecific confrontations among Ca. rufifemur colonies yielded a gradient from allocolonial tolerance to strong aggression. The aggression patterns coincide with those of Cr. modiglianii towards Ca. rufifemur workers from the same colonies. Our results suggest either that Ca. rufifemur is not able to recognize allocolonial Cr. modiglianii workers as foreign or that they are recognized but tolerated. The unilateral, species-specific but not colony-specific tolerance of Ca. rufifemur towards its partner species contrasts with highly colony-specific tolerance found among neotropical parabioses.