Ants (Temnothorax nylanderi) adjust tandem running when food source distance exposes them to greater risks

Abstract

Social insect colonies exploit food sources that vary in their profitability and riskiness. One factor that affects both profitability and riskiness is the foraging distance: more distant resources are both more costly to exploit and expose individuals to greater predation or navigational risks. Temnothorax nylanderi scouts use tandem running to recruit nestmates to resources, such as food or nest sites. Tandem runs are often unsuccessful, leaving followers in potentially unknown or dangerous territory. Thus, as foraging distances increase, communication mistakes are likely to be more costly. We tested if leaders and followers adjust their tandem running behavior in response to increasing foraging distances. We asked whether the success rate, the probability to recruit, and the waiting time following a loss of contact depend on the foraging distances. We found that the success rate (75–86%) of tandem runs does not decrease with increasing foraging distance but rapidly increases with the leader’s experience, from 67% for the first tandem run to 94% for the fourth. Pairs progressed faster, and followers search longer for their partner after a loss of contact when visiting more distant food sources. The probability to perform a tandem run did not decrease with the foraging distance but increased with foraging experience. Our results indicate that ants might attempt to reduce exposure to risks by progressing faster when visiting more distant food sources. As ants become more experienced, they lead more and better tandem runs. These findings suggest that both leaders and followers respond to the potential dangers posed by exploiting faraway resources.

Significance statement

Foraging distance plays an important ecological role in animals as the foraging distance affects both energetic costs and predation risk. Ants have evolved several cooperative foraging strategies to exploit a food source as efficiently as possible, including a recruitment method called “tandem running.” Here, an informed leader guides a naïve follower to a valuable resource. We tested if tandem running behavior changes if food sources are more distant. Foraging distance indeed had an impact as leaders walked faster and followers searched for longer after a contact loss when food sources were more distant.