Diacammaants adjust liquid foraging strategies in response to biophysical constraints

Abstract

Ant foragers provide food to the rest of the colony, often requiring transport over long distances. Foraging for liquid is challenging because it is difficult to transport and share. Many social insects store liquids inside the crop to transport them to the nest, and then regurgitate to distribute to nest-mates through a behaviour called trophallaxis. Some ants instead transport fluids with a riskier behaviour called pseudotrophallaxis—holding a drop of liquid between the mandibles through surface tension. Ants share this droplet with nest-mates without ingestion or regurgitation. We hypothesised that ants optimize their liquid-collection approach depending on viscosity. Using an ant that employs both trophallaxis and pseudotrophallaxis, we investigated the conditions where each liquid-collection behaviour is favoured by measuring biophysical properties, collection time and reaction to food quality for typical and viscosity-altered sucrose solutions. We found that ants collected more liquid per unit time by mandibular grabbing than by drinking. At high viscosities ants switched liquid collection method to mandibular grabbing in response to viscosity and not to sweetness. Our results demonstrate that ants change transport and sharing methods according to viscosity–a natural proxy for sugar concentration–thus increasing the mass of sugar returned to the nest per trip.

Three-dimensional body reconstruction enables quantification of liquid consumption in small invertebrates

“…Interestingly, if viscosity is artificially manipulated, and a low sucrose concentration solution is made to be highly viscous, ants rapidly decrease their pump frequency, resulting in demotivation for the food source (Lois-Milevicich, Schilman & Josens, 2021). In some species, high viscosity solutions can even trigger a switch from trophallaxis – where ants ingest a liquid and later share it with their nestmates – to pseudotrophallaxis – where ants hold a liquid drop between their mandibles through surface tension and later share it with their nestmates without ingestion (Fujioka, Marchand & LeBoeuf, 2023).…”

“…Ants are expected to prefer and consequently ingest more food when the sucrose concentration - and thus the energy provided by the solution - is higher. However, the high viscosity of these solutions is expected to decrease the rate at which the ants can ingest the food (Sola & Josens, 2016; Fujioka, Marchand & LeBoeuf, 2023). Lastly, we fed the ants a range of caffeine-laced sucrose solutions in order to assess their preference or aversion for them.…”