Tandem Recruitment and Foraging in the Ponerine Ant Pachycondyla harpax (Fabricius)

Abstract

Tandem running is a common recruitment strategy in ant species with small colony sizes. During a tandem run, an informed leader guides a usually naïve nestmate to a food source or a nest site. Some species perform tandem runs only during house hunting, suggesting that tandem running does not always improve foraging success in species known to use tandem running as a recruitment strategy, but more natural history information on tandem running under natural conditions is needed to better understand the adaptive significance of tandem recruitment in foraging. Studying wild colonies in Brazil, we for the first time describe tandem running in the ponerine ant Pachycondyla harpax (Fabricius). We asked if foragers perform tandem runs to carbohydrate- (honey) and protein-rich (cheese) food items. Furthermore, we tested whether the speed and success rate of tandem runs depend on the foraging distance. Foragers performed tandem runs to both carbohydrate food sources and protein-rich food items that exceed a certain size. The probability to perform a tandem run and the travelling speed increase with increasing foraging distances, which could help colonies monopolize more distant food sources in a competitive environment. Guiding a recruit to a food source is costly for leaders as ants are ~66% faster when travelling alone. If tandem runs break up (~23% of all tandem runs), followers do not usually discover the food source on their own but return to the nest. Our results show that tandem running to food sources is common in P. harpax, but that foragers modify their behaviour according to the type of food and its distance from the nest. Competition with other ants was intense and we discuss how tandem running in P. harpax might help colonies to build-up a critical number of ants at large food items that can then defend the food source against competitors.

Revisiting the ideas of trees as templates and the competition paradigm in pairwise analyses of ground-dwelling ant species occurrences in a tropical forest

“…Ant species that are frequent users of EFN are known to nest closer to EFN-producing plants (Silva et al, 2019). Pachycondyla harpax usually nests underground in the vicinity of trees (Grüter et al, 2018), and although workers forage primarily on the ground, they can also be found on trees (Rocha et al, 2015). However, if P. harpax attends EFNs on I. edulis and P. gonoachanta trees needs to (Wang et al, 2016).…”

Large body size variation is linked to low communication success in tandem running ants

“…Even though some lost followers may discover the new nest by themselves (Pratt 2008; Franks et al 2010), unsuccessful tandem runs often represent a loss of time because lost followers require more time to discover a resource or they have to return to their nest following a break-up (Franks and Richardson 2006; Basari et al 2014b; Grüter et al 2018). Furthermore, a breakup could leave followers in unknown and dangerous locations.…”

“…A recruitment behaviour that relies on communication and that could be negatively affected by body size differences is tandem running, which is relatively common in ant species with small colony sizes (so far described in ~40 species) (Beckers et al 1989; Franklin 2014; Grüter et al 2018). During a tandem run, a leader with information about the location of a resource slowly guides a nestmate to a food source or a nest site.…”

“…Nonetheless, a substantial proportion of tandem runs break up before reaching the goal (e.g. ~19% in Temnothorax nylanderi , Glaser and Grüter 2018; ~23% in Pachycondyla harpax , Grüter et al 2018; ~50% in Cardiocondyla venustula , Wilson 1959; up to 70% in Temnothorax rugatulus , Pratt 2008). Break-ups are costly in terms of time and could leave lost followers in dangerous areas.…”

Ants’ Personality and Its Dependence on Foraging Styles: Research Perspectives

“…The authors suggested that tandem running is the evolutionary precursor of odor-trail communication. In some species, the tandem running technique is only used during "house-hunting, " whereas other species explore tandem running in both migration and foraging (review in Grüter et al, 2018). This recruitment system has been considered to be a primitive one since only one nestmate is recruited at a time.…”