Karen L. Hollis

In a species of Mediterranean desert-dwelling ant, Cataglyphis piliscapa (formerly, C. cursor), some individuals, mostly foragers, engage in highly orchest

Previous research in our laboratories has demonstrated that, within each colony of Cataglyphis piliscapa (formerly C. cursor) ants, only some individuals a

In colonies of Cataglyphis cursor ants, a single queen mates with multiple males, creating the foundation for heritable behavioral specializations. A novel and unique candidate for such specializations is rescue behavior, a precisely delivered form of altruism in which workers attempt to release trapped nestmates and which relies on short-term memory of previous actions to increase its efficiency. Consistent with task specialization, not all individuals participate; instead, some individuals move away from the victim, which gives rescuers unrestricted access. Using a bioassay to identify rescuers and non-rescuers, coupled with paternity assignment via polymorphic microsatellite markers, we not only show that rescue behavior is heritable, with 34% of the variation explained by paternity, but also establish that rescue, heretofore overlooked in analyses of division of labor, is a true specialization, an ant version of first responders. Moreover, this specialization emerges as early as 5 days of age, and the frequency of rescuers remains constant across ants’ age ranges. The extremely broad range of these ants’ heritable polyethism provides further support for the critical role of polyandry in increasing the efficiency of colony structure and, in turn, reproductive success.

Cataglyphis cursor worker ants are capable of highly sophisticated rescue behaviour in which individuals are able to identify what has trapped a nestmate and to direct their behaviour towards that obstacle. Nonetheless, rescue behaviour is constrained by workers’ subcaste: whereas foragers, the oldest workers, are able both to give and to receive the most help, the youngest workers, inactives, neither give nor receive any help whatsoever; nurses give and receive intermediate levels of aid, reflecting their intermediate age. Such differences in rescue behaviour across subcastes suggest that age and experience play a critical role. In this species, as in many others in which a sensitive period for nestmate recognition exists, newly enclosed ants, called callows, are adopted by ants belonging not only to different colonies but also to different species; foreign callows receive nearly the same special care provided to resident newborns. Because callows are younger than inactives, which are incapable of soliciting rescue, we wondered whether entrapped callows would receive such aid. In the present study, we artificially ensnared individual callows from their own colony (homocolonial), from a different colony (heterocolonial), and from a different species (heterospecific), and tested each one with groups of five potential C. cursor rescuers, either all foragers or all nurses. Our results show that all three types of callows are able to elicit rescue behaviour from both foragers and nurses. Nonetheless, nurse rescuers are better able to discriminate between the three types of callow victims than are foragers.