Pheromone communication in ants: a detailed analysis of concentration-dependent decisions in three species

Abstract

The collective behavior of ants and the emergence of self-organizing patterns in ant colonies have been explained with various theoretical approaches based on models of trail following behavior elicited by pheromones. Although existing models can explain collective behavior of ants, there is little empirical evidence on how ants precisely respond to various pheromone concentrations. Thus, important knowledge is lacking about how much realistic description of ant behavior can be provided by the models and their underlying mathematical functions. To fill in this gap, we conducted experiments with three different ant species to explore their responses to varying concentrations of pheromones that elicit ants' trail following behavior. We found that ants' decision making processes in trail following are best explained by psychophysical theory (PT), which describes the relationship between physical stimuli, sensory perception and decision making in humans, other primates, birds and insects. Furthermore, the theory provides clear definitions of biological parameters, such as detection-and discrimination thresholds. The species studied were distinctively different in the shape and parameters of their psychometric functions, which we attribute to specific adaptions to their environment. The observed differences are discussed in relation to their natural trail following behaviors. Our study opens a new perspective of understanding and explaining important aspects of collective ant behavior using a wellestablished theory of perception.

Modulation of trail laying in the ant Lasius neglectus (Hymenoptera: Formicidae) and its role in the collective selection of a food source

“…In other species, it has been shown that multiple pheromones can be selectively released by one or more glands to cope with different tasks (Jackson & Ratnieks, 2006), such as distinguishing between raid and emigration trails (Witte & Maschwitz, 2002), or to more quickly change trail direction when it is required by sudden environmental changes (Dussutour et al, 2009). Moreover, it appears that a signal can be changed by modulating the pressure of the gaster on the substrate and the pheromone concentration in the released droplet (Hangartner, 1969;Jackson & Châline, 2007;von Thienen, Metzler, Choe, & Witte, 2014). Finally, U-turn behaviour, also described in L. niger and M. pharaonis, might be involved and help orient the collective foraging towards the most rewarding resource (Beckers, Deneubourg, & Goss, 1992b;Hart & Jackson, 2006), although, in our study, we observed this behaviour only 13 times in total in our marking experiments.…”

Information synergy: adding unambiguous quality information rescues social information use in ants

“…The new arm was either marked with a pheromone trail (treatments F-J) or not (treatments A-E). This pheromone trail was produced by immersing 8 worker hindgut glands in 2ml of dichloromethane (DCM), following von Thienen et al [42]. 5.6μl of this mixture was applied in an even line along the paper overlay covering the arm, using a capillary tube (Servoprax GmbH, Germany).…”

Irrational risk aversion in ants is driven by perceptual mechanisms

“…Secondly, the presence of odours on a path affects pheromone deposition: while pheromone deposition on odourless paths is usually higher on the nestward journey (Beckers et al, 1993;Czaczkes and Heinze, 2015;Czaczkes et al, 2013Czaczkes et al, , 2016, pheromone deposition is higher on outward journeys on scented paths (this study, Czaczkes et al, 2018bCzaczkes et al, , 2018c. Finally, it should be noted that perception of pheromone, much like perception of quality, is also logarithmic (von Thienen et al, 2014), thus emphasising initial differences in pheromone concentration but damping out differences between strong trails. Nevertheless, it seems that colony-level decision-making effectively filters out the ants individual perceptual constrains (this study, Sasaki and Pratt, 2011), but the mechanism used to achieve this is still unknown.…”