Nutrient stores predict task behaviors in diverse ant species

Abstract

In eusocial species, including ants and honeybees, sterile or non-reproductive workers can specialize in task-specific behaviors, such as brood care and foraging for food. The mechanisms underlying task-specific behaviors include genetic, physiological and environmental factors. Here we compare corporeal nutrient storage in nine species that differ in primary food preferences (carbohydrate-, protein-or lipid-based diet) to test whether foraging behavior is associated with lower individual nutrient stores. We also investigate whether low nutrient stores are limited to foragers or occur in other external, morphologically distinct, worker sub-castes. In six out of eight species where both brood care workers and foragers were sampled, foragers had significantly lower nutrient stores relative to brood care workers; the exceptions were two Solenopsis species. Foragers from five of these six species had lower lipid levels, supporting the link between lipid content and foraging behaviors reported in previous studies. Interestingly, three species had lower levels of both lipid and carbohydrate stores in foragers relative to brood care workers, and foragers of one species, Formica fusca, had lower carbohydrate levels but not lipid levels, suggesting that the association between nutrient stores and foraging behavior is not universal across ant species or across all seasons. In all three species with morphologically distinct sub-castes, lipid levels were lowest in non-foraging, external workers, i.e., majors or soldiers, indicating an additional link between nutrient depletion and the allocation of external tasks other than foraging.

Oxytocin‐like signaling in ants influences metabolic gene expression and locomotor activity

“…8 and 9); and 3 ) isolated, single nurses of Camponotus rufiper exhibit higher locomotor activity as compared with foragers (56). Additionally, in many ant species nurses contain higher fat (or other nutrient) stores as compared with foragers (55), which agrees with our results and interpretation that nurses had a lower expression of the inotocin signaling system components, which correlates to higher fat reserves.…”

“…5). Because foragers contain lower amounts of lipids as compared with nurses (55) and because nurses and foragers exhibit differences in feeding behavior (56), we collected 20 ants from the foraging area and brood chamber and determined the expression of the IP and IR in the respective individuals. We found that expression of the IP and IR of nurses was significantly reduced (by ~70%; P ≤ 0.0243, Student’s t test) (Fig.…”

The Role of Dopamine in the Collective Regulation of Foraging in Harvester Ants

“…Second, changes in dopamine signaling could alter the forager's perception of its own physiological state or the harshness of the environment, including low humidity. Self-evaluation of physiological state is important in the regulation of individual foraging activity in other ant species ( Robinson et al., 2012 , Silberman et al., 2016 ), and dopamine can influence the evaluation of environmental stimuli and organismal state ( Barron et al., 2015 , Friston et al., 2012 , Scaplen and Kaun, 2016 ). Thus, increases in dopamine signaling may lead dopamine-treated P. barbatus foragers to overestimate their physiological readiness for foraging given the perceived humidity, and vice-versa for 3IY-treated foragers.…”

Gene expression is stronger associated with behaviour than with age and fertility in ant workers

“…Nutritional status, with corpulent brood carers and food deprived foragers, is one of the most widespread and consistent factors mediating worker behaviour [10,19], and influences gene expression in honey bees [12,18,22,25,26,28] and wasps [29]. In ants however, despite the broad correlative evidence for brood carers harbouring more lipid storages than foragers [6–9,14,94,95], clear transcriptomic signatures of nutritional status have so far not been found [30,31]. Only a single study identified lipid storage and fatty acid metabolism to be enriched functions of genes differentially expressed between brood carers and foragers [96].…”