Nutritional regulation influencing colony dynamics and task allocations in social insect colonies

The ability of social insect colonies to recruit nestmates to profitable resources increases colony-wide foraging efficiency by providing individuals with information that narrows their search for resources. Here we ask if for the Neotropical swarm-founding waspPolybia occidentalisnaïve nestmates are able to use food-scent cues from rich carbohydrate resources brought to the nest by successful foragers to orient to off nest resources. Foragers were allowed to freely visit a training dish containing a scented sucrose solution. At a second location, in a different direction from the nest, two sucrose-filled dishes were offered, one with the training scent and one with an alternate scent. Naïve foragers preferentially chose the training scent over the alternate scent, indicating that natural rates of resource inflow to the nest are sufficient to induce nestmates to forage at resources with a specific scent. Naïve foragers did not forage more often at the location at which the active foragers were foraging, an indication that directional information is not communicated in this species. The total number of foraging trips made by a colony's foragers was not determined by the size of the foraging force, but rather by the average individual foraging rate for the colony.

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Pharaoh ant colonies dynamically regulate colony demography by culling young queen and male-destined larvae

10.1101/211573 ◽

2017 ◽

Author(s):

Michael R. Warner ◽

Jessica Lipponen ◽

Timothy A. Linksvayer

Keyword(s):

Resource Allocation ◽

Social Insect ◽

Molecular Mechanisms ◽

Allocation Of Resources ◽

Dynamic Allocation ◽

Individual Level ◽

Colony Demography ◽

Insect Colonies ◽

Egg Density ◽

Colony Level

AbstractThe success of social insect colonies is dependent upon efficient and dynamic allocation of resources to alternate queen and worker castes. The developmental and molecular mechanisms regulating the caste fate of individual larvae in response to environmental cues have been the focus of intense study. However, the mechanisms regulating colony-level resource allocation into alternate castes (i.e. caste allocation ratios) are less well studied. Here, we systematically manipulate colony demography to elucidate the social regulatory mechanisms of caste allocation in the antMonomorium pharaonis. We find that differences in caste allocation result from differences in timing and efficiency of culling of very young reproductive-destined larvae, which are always present in colonies. Based on our results, we develop a conceptual model depicting how colonies integrate numerous individual-level caste determination decisions to regulate colony-level caste allocation. We propose that adult workers make decisions about culling larvae based on the ratio of the number of workers to the number of eggs contained in colonies, likely signalled by pheromone present on eggs. This strategy is a bet-hedging strategy which enables the dynamic alteration of colony demography in response to internal and external conditions. The strategy is likely key to the ability ofM. pharaonisand similar ants to thrive in disturbed habitats and to become widespread invasive species.Significance StatementThe defining feature of social insect societies is the presence of alternate queen (reproductive) and worker (non-reproductive) castes of individuals. The fitness of social insect colonies is dependent upon efficient allocation of resources to alternate castes, particularly in the case of highly polygynous (multi-queen) societies. However, the mechanisms by which such societies regulate caste allocation are largely unknown. In this study, we show that colonies manipulate their production of queens (and also males) versus workers according to the present density of eggs in the colony, which serves as a reliable indicator of queens’ fertility. Provided egg density is high, colonies kill queen-and male-destined larvae; when egg density falls, colonies begin to rear queens and males. This flexible resource allocation strategy is key to the ability of highly polygynous species to thrive in marginal (often human-associated) habitats.

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