Abstract:
Specialized defence traits and strategies are crucial in surviving enemy attacks and in resource acquisition. In numerous social insect lineages, soldiers function as specialized defence traits of the colony, but associated defence strategies are poorly known. The turtle ant Cephalotes rohweri is an obligate cavity-nesting ant with highly specialized soldiers. To maximize growth and reproduction, colonies must use their limited availability of soldiers to defend multiple cavities. Using laboratory experiments informed by field data, we addressed how soldier 'deployment' across cavities adjusts to changes in cavity availability and quality. From initial field-like conditions, soldier deployment to newly available cavities was rapid, stabilized quickly, and at least doubled the number of cavities defended by each colony. New cavities were defended by fewer soldiers than original cavities still in use. Nevertheless, when new cavities differed in size, an important quality metric, large cavities were used more often and defended by more soldiers than small cavities. Despite these dynamic responses, total soldier deployment to new cavities was limited to an approximately constant proportion (0.4) of overall soldier availability across colonies and resource contexts. Moreover, there was a significant positive relationship between total soldier deployment to new cavities (greater for larger colonies) and both the number of newly defended cavities and their average level of defence. These results demonstrate that colony-wide soldier deployment is dynamic, predictable and context sensitive but ultimately constrained by the availability of soldiers in the colony. Furthermore, the consistently lower number of soldiers in new cavities, which always limits the potential losses to enemies, is concordant with a 'conservative bet-hedging' life history strategy. Broadly, our findings show that a specialized soldier caste can be associated with a far more sophisticated defence strategy than previously recognized. This provides a more complete perspective on the evolution of soldier-based defences in insect societies. © 2012 The Association for the Study of Animal Behaviour.
Abstract:
Bees may leave their nest in the event of an attack, but this is not their only response. Here, we examine the behavior of those individuals that remain inside the nest during a disturbance. Specifically, we test the hypothesis that bee workers usually exhibiting high levels of inactivity (i.e., 'lazy' bees) may function as defensive reserves that are more likely to respond when the colony is disturbed. We explore this hypothesis by simulating vertebrate attacks by vibrating or blowing carbon dioxide into two colonies on alternating days and measuring the movements and tasks performed by bees inside the nest. Our results show that regardless of the disturbance type, workers increase guarding behavior after a disturbance stops. Although previously inactive bees increased their movement speed inside the nest when the disturbance was vibration, they were not more likely to leave the nest (presumably to attack the simulated attacker) or switch to guarding behavior for any disturbance type. We therefore reject the hypothesis that inactive Bombus impatiens bumblebees act as defensive reserves, and propose alternative hypotheses regarding why many workers remain inactive inside the nest. © International Union for the Study of Social Insects (IUSSI) 2012.
Consistent individual variation in animal behaviour is nearly ubiquitous and has important ecological and evolutionary implications. Additionally, suites of behavioural traits are often correlated, forming behavioural syndromes in both humans and other species. Such syndromes are often described by testing for variation in traits across commonly described dimensions (e. g. aggression and neophobia), independent of whether this variation is ecologically relevant to the focal species. Here, we use a variety of ecologically relevant behavioural traits to test for a colony-level behavioural syndrome in rock ants (Temnothorax rugatulus). Specifically, we combine field and laboratory assays to measure foraging effort, how colonies respond to different types of resources, activity level, response to threat and aggression level. We find evidence for a colony level syndrome that suggests colonies consistently differ in coping style-some are more risk-prone, whereas others are more risk-averse. Additionally, by collecting data across the North American range of this species, we show that environmental variation may affect how different populations maintain consistent variation in colony behaviour.
