Diacammaants adjust liquid foraging strategies in response to biophysical constraints

Abstract

Ant foragers need to provide food to the rest of the colony, which often requires food transport over long distances. Foraging for liquid is especially challenging because it is difficult to transport and share. Many social insects store liquid food inside the crop to transport it to the nest, and then regurgitate this fluid to distribute it to nestmates through a behaviour called trophallaxis. Some ants instead transport fluids with a riskier behaviour—holding a drop of liquid between the mandibles through surface tension—after which the ant shares this droplet with nestmates without ingestion or regurgitation in a behaviour called pseudotrophallaxis. Here, we hypothesized that ants optimise their liquid-collection approach depending on food quality and biophysical properties. Working with a ponerine ant that uses both trophallaxis and pseudotrophallaxis, we investigated why each liquid-collection behaviour might be favored under different conditions by measuring handling time and liquid viscosity and reaction to food quality (i.e., sugar concentration and viscosity) using a viscosity additive. We found that ants could collect more liquid food per unit time by mandibular grabbing than by drinking. At high viscosities, which in nature correspond to high sugar concentrations, ants switched their liquid collection method to mandibular grabbing in response to viscosity, and not to sweetness. In addition, mandibular grabbing of liquid food allowed ants to carry more sugar per unit time than drinking. Our results demonstrate that ants change not only their feeding preference but also their transport and sharing methods according to viscosity—a proxy for sugar concentration in nature—optimising the mass of sugar returned to the nest over time.

Ecological change and conflict reduction led to the evolution of a transformative social behavior in ants

“…In the two early gains of trophallaxis ( Ectatomminae species lost worker reproductive potential rather late, about 40-25 Ma, and yet they still do not perform true trophallaxis. This indicates that there was either some form of critical period connected to ecological changes, or that these species may be transitioning to using trophallaxis, perhaps through mandibular pseudotrophallaxis 16,25 . In multiple other subfamilies, the species present in our dataset never evolved trophallaxis in accordance with our hypothesis (Leptanillinae, Apomyrminae, Proceratiinae, Amblyoponinae and Agroecomyrmecinae, Fig 2): sugary liquids were never integrated into the diet, workers lost full reproductive potential, and trophallaxis never evolved.…”

“…A majority of ecosystem-dominating generalist ants perform a behavior called stomodeal trophallaxis, wherein adult workers regurgitate the contents of their crop to nestmates in a mouth-to-mouth interaction 14 , though it is not clear why these traits appear to co-vary. It has been suggested that trophallaxis behavior evolved to transport sugary liquids acquired through mutualisms with sapsuckers or with plants 15,16 . Species that use trophallaxis tend not to have a sting and tend to have sterile workers or workers that cannot be mated, suggesting that these traits might prohibit the evolution of trophallaxis 14 .…”

Using pupae as appetitive reinforcement to study visual and tactile associative learning in the Ponerine ant Diacamma indicum

“…A longer waiting time between subsequent unloading interactions is experienced by honey bee foragers if the colony is satiated 52 ; among ants, receiving a particular type of food 53 and deprivation of required nutrients 54 leads to colony satiation. The viscosity of food source (sugar) impacts the number of trips and method through which sucrose solution is shared by nestmates in D. indicum 55 , 56 . D. indicum foragers are solitary scavengers that occasionally hunt for termites.…”

Diacammaants adjust liquid foraging strategies in response to biophysical constraints

“…Data accessibility. All data and codes are available at: https://doi.org/ 10.5061/dryad.x95x69png [57].…”