Abstract
Eusocial insects can express surprisingly complex cooperative defence of the colony. Brood and reproductive castes typically remain in the nest and are protected by workers' various antipredator tactics against intruders. In Madagascar, a myrmicine ant, Aphaenogaster swammerdami, occurs sympatrically with a large blindsnake, Madatyphlops decorsei. As blindsnakes generally specialize on feeding on termites and ants brood by intruding into the nest, these snakes are presumably a serious predator on the ant. Conversely, a lamprophiid snake, Madagascarophis colubrinus, is considered to occur often in active A. swammerdami nests without being attacked. By presenting M. colubrinus, M. decorsei and a control snake, Thamnosophis lateralis, at the entrance of the nest, we observed two highly specialized interactions between ants and snakes: the acceptance of M. colubrinus into the nest and the cooperative evacuation of the brood from the nest for protection against the ant-eating M. decorsei. Given that M. colubrinus is one of the few known predators of blindsnakes in this area, A. swammerdami may protect their colonies against this blindsnake by two antipredator tactics, symbiosis with M. colubrinus and evacuation in response to intrusion by blindsnakes. These findings demonstrate that specialized predators can drive evolution of complex cooperative defence in eusocial species.
Highlights
Eusocial insects can express surprisingly variable and complex cooperative behaviours [1]
The worker ants exhibited an aggressive reaction towards T. lateralis, no reaction towards M. colubrinus and immediate cooperative evacuation of pupae and larvae in response to M. decorsei
Significant differences in the number of biting ants were detected in M. decorsei versus M. colubrinus ( p = 0.014) and T. lateralis versus M. colubrinus ( p < 0.001), but not in M. decorsei versus T. lateralis ( p = 0.316; table 1 and figure 1c)
Summary
Eusocial insects can express surprisingly variable and complex cooperative behaviours [1] Their adult colony members are divided into reproductive and non-reproductive (or at least less-reproductive) castes. The colonies of a myrmicine ant distributed in Madagascar, Aphaenogaster swammerdami, include approximately 100–1500 workers and inhabit large, underground nests that have one large entrance hole and a conspicuous mound [8,9] This ant occurs sympatrically with a large blindsnake, Madatyphlops decorsei. It is called ‘Ant’s Mother’ by local people of Madagascar [14,15,16,17] Because both the ‘Ant’s Mother’ and the blindsnake are likely to frequently enter the nest, and the latter can inflict intense predation pressure on the ant brood, we hypothesized that ant workers discriminate between and respond differently to predatory and non-predatory snake species. We presented M. decorsei, M. colubrinus and Thamnosophis lateralis (a sympatric frog-eating snake as control) at the entrance of A. swammerdami nest and compared the responses of ants to them
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