Deby L. Cassill

Nest complexity, group size and brood rearing in the fire ant, Solenopsis invicta

Summary: Colonies of the monogyne social form of the red imported fire ant, Solenopsis invicta, may contain half a million workers per nest. Spatially organizing such a large group within the confines of a single nest requires a pragmatic architectural design. The morphology of field mounds and subterranean nest chambers of S. invicta were determined using several cast methods. The above-ground portion of a fire ant nest, the mound, consisted of a dense matrix of narrow tunnels. Below ground level, subterranean shafts and nodes were excavated through the grass root system (10-20 cm), connecting the mound tunnels to the subterranean chambers. Chambers averaged ∼ 5cm2 and appeared at depths from 10-80 cm below ground level. The orientation of mound tunnels and subterranean shafts was more often vertical than horizontal, probably facilitating the diurnal micro-migration of colony members back and forth from the subterranean chambers to the mound. The mean size of groups in the subterranean chambers of field nests was remarkably small relative to colony size (∼200 individuals per chamber: 50% workers, 50% brood). In laboratory experiments, neither crowding nor nest partitioning affected brood rearing. The possibility that small group size and nest complexity generate localized or time-released communication signals is discussed.

Skew Selection: Nature Favors a Trickle-Down Distribution of Resources in Ants *

Synopsis: According to skew selection, ant queens are neither ruthlessly selfish nor blindly altruistic; they are shrewd investors. The goal of shrewd investors is not to win the game, but to continue play over evolutionary time. Skew selection describes a set of investment strategies employed by players such as ant queens to keep the game going. First, ant queens acquire excess resources—more than they need for immediate survival and reproduction. Second, queens invest a portion of their excess resources in personal capital to maintain dominant status. Third, queens also invest a portion of excess resources in low-quality offspring to gain group capital. Fourth, when investing in group capital, resources are distributed in a trickle-down fashion to maintain the largest number of diminishing-quality offspring possible. The trickle-down redistribution allows the shrewd queen to increase group size (safety in numbers) and, at the same time, maintain individual status (safety in position). According to skew selection, queens invest in low-quality offspring (sterile workers) to buffer hereself and her high-quality offspring from agents of death such as war, predation or disease.

Cooperation during prey digestion between workers and larvae in the ant, Pheidole spadonia

Abstract.Digestion and distribution of nutrients are central to the growth and reproduction of social insect colonies, just as they are to individual organisms. In the case of eusocial insect species, different components of food handling and processing can be distributed among castes. This paper reports on an ant species, Pheidole spadonia, in which the adult workers butcher prey and 4th instar larvae dissolve prey for distribution among other colony members including workers, larvae and queens. To characterize the process, six groups, each composed of twenty-five workers and thirty larvae, were provisioned with a fruit fly carcass, and then video-taped continuously for 24 hours. On average, five adult workers and twenty-two 4th instar larvae invested 12.8 labor hours into butchering and predigesting one fly carcass. Workers contributed a mean total of 3.3 labor hours to butcher the carcass into small fragments. Fourth instar larvae contributed a mean total of 9.5 labor hours to pre-orally dissolve the solid fragments. Surprisingly, larvae did not ingest during the dissolving process. Instead, workers ingested the dissolved prey tissue into their crops and then regurgitated it to colony members, larvae and workers, that solicited for feedings. The cooperative interactions reported here between workers and larvae extend the mechanistic and evolutionary explanations for eusociality.

Information flow during social feeding in ant societies

In fire ants, social feeding is regulated by two hungers, one among larvae, the other among workers. Workers donate to larvae or to workers hungrier than themselves, and solicit from workers more satiated than themselves. Food flows via a chain of demand initiated by hungry solicitors rather than a chain of transfer initiated by full donors.

Young fire ant workers feign death and survive aggressive neighbors

Feigning death is a method of self-defense employed among a wide range of prey species when threatened by predator species. This paper reports on death-feigning behavior by the fire ant, Solenopsis invicta, during intraspecific aggression among neighboring fire ant workers. Days-old workers responded to aggression by death feigning, weeks-old workers responded by fleeing and months-old workers responded by fighting back. By feigning death, days-old workers were four times more likely to survive aggression than older workers. From a proximate perspective, retaliation by young workers against aggressive older workers is certain to fail. With their relatively soft exoskeleton, young workers would be prone to injury and death and unable to execute an effective attack of biting or stinging older workers with harder exoskeletons. From an ultimate perspective, death feigning allows young workers to survive and contribute to brood care and colony growth, both of which are essential to queen survival and fitness.

Brood Care Strategies by Newly Mated Monogyne Solenopsis invicta (Hymenoptera: Formicidae) Queens During Colony Founding

Abstract For most species of ants, newly mated queens found new colonies from stored body reserves, and without the assistance of workers. Consequently, until the first batch of colony members hatches, newly mated queens face a potential shortage of labor for brood care. The purpose of this study was to describe the brood rearing strategies of newly mated monogyne Solenopsis invicta queens, under controlled laboratory conditions, to determine how they compensated for the lack of worker labor in rearing the first batch of colony members. Newly mated S. invicta queens were collected (n = 60) and reared individually in artificial nests in the laboratory under optimal incubation conditions. Using video-technology, brood care activity by newly mated queens was quantified and compared with brood care activity of mature queens who were incubated with workers. In addition, newly mated queens and their offspring (i.e., the incipient colony) were censused biweekly for 6 mo to determine the ontogeny of the adult:larva ratio. Results from this study revealed that newly mated queens spent 65% of their time engaged in brood care activities; queens incubated with workers spent <1% of their time tending brood. Newly mated queens laid two kinds of eggs, viable and trophic. Trophic eggs were ingested by the queen, and then regurgitated to larvae. In the second phase of colony founding, after the first worker offspring hatched, the adult:larva ratio was >1:1. Consequently, larvae were never in competition with each other for worker attention. In summary, this study revealed that newly mated queens were endowed with a suite of compensatory brood rearing strategies enabling them to succeed in founding a colony in the absence of worker labor.

Effects of Larval Secretions on Queen Fecundity in the Fire Ant

Abstract For social insects, queen fecundity is central to queen survival. In addition, coordinating workload, in the form of hungry larvae, with labor, in the form of workers, is critical to queen survival. Such coordination is accomplished by transporting waste products from molting fourth instars to queens that then amplify queen egg production. The source of the fecundity-amplifying factors that are transmitted from larvae to queens is still under debate. This article reports a case study on the red imported fire ant, Solenopsis invicta Buren, demonstrating that larval excretory products amplified queen fecundity rather than larval fecal fluids, larval saliva, or nutrients. Queens were active participants in their intake of fecundity-amplifying factors, often grazing over larvae, squeezing and ingesting the expelled droplet. In summary, these findings support a queen-centered rather than a worker-centered model for the social regulation of queen fecundity and survival.

MOGUL GAMES: IN DEFENSE OF INEQUALITY AS AN EVOLUTIONARY STRATEGY TO COPE WITH MULTIPLE AGENTS OF SELECTION

In this paper, we propose that the “powerful and privileged” sustain their way of life through greed and they sustain the lives of others through trickledown sharing. Greed provides the powerful and privileged a buffer against famine. Trickledown sharing provides them a buffer against predation or war. The inspiration for this integration of greed and trickledown sharing as self-preservation strategies is a multi-selection model called skew selection. According to skew selection, when perennial organisms are subjected to cycles of famine and predation, greed and trickledown sharing increases the organism’s survival relative to a greed-only strategy. Skew selection is extended to explain greed and trickledown sharing among humans through the introduction of mogul games. The results of mogul games reported herein suggest that inequality is an emergent property of self-organizing systems and potentially an essential precursor to the evolution of social behavior. In the future, it is our hope that mogul game simulations will be employed by others to explore the effect of variation in cycles of predation and resource abundance on the rules of greed (resource acquisition) and trickledown sharing (resources redistribution).

Modeling temperature-mediated fluctuation in colony size in the fire ant, Solenopsis invicta.

In the social insects, colony size is central to the survival of the queen. Two endogenous factors, worker longevity and queens daily egg production, are known to determine maximum colony size. A third endogenous factor, duration of worker development from egg to adult, regulates the rate of colony growth. In this paper, we report findings from a simulation quantifying the effects of temperature on colony size in the fire ant, Solenopsis invicta. The monthly average temperature over a six year period for the panhandle of north Florida was interpolated to determine the effects of daily temperature on a queens egg production, worker developmental time and worker longevity. Additional daily temperatures were simulated: 7°C higher and 7°C lower than daily temperatures for north Florida. As expected, colony size was the largest when annual temperatures were the highest across seasons, ranging from 57,000 to 187,000. Colony size at intermediate daily temperatures ranged from 14,000 to 103,000; small colonies recovered rapidly as temperatures warmed. Colony size at lower daily temperatures ranged from 14,000 to 21,000. Extended worker longevity at lower temperatures compensated for low egg production and longer developmental time. And vice versa, the queens high rate of egg production and the shorter developmental time compensated for shorter worker longevity at high temperatures. Because the fire ant nest consists of a heat-collecting dome in which to incubate brood during cold weather, and deep chambers in which to cool workers during hot weather, colony size is likely to be higher and more stable than our simulation showed. The extended longevity of workers and queens at low temperatures, and perhaps their ability to hibernate below the permafrost, might explain the ability of ants to colonize habitats worldwide.

A Naturological approach to corporate governance : An extension of the frederick model of corporation-community relationships

Naturological systems contain two bases of power: personal and group capital. Profit seeking and profit sharing are mechanisms by which capital is obtained. For example, acquiring profits in the form of body fat, food caches, and prime territory allows organisms to survive scarcity; likewise, profit sharing appeases those who might otherwise steal resources. Moreover, sharing is a cost-effective way for organisms to avoid predation. Complementary powers of nature are applicable to corporations, with implications for governance. Corporate environments dominated by recessions and takeovers (the equivalent of scarcity and predation) require investors, management, and boards (the wealthy) to share profits with employees and the surrounding community (the masses) for long-term survival. To explore these mutualistic relationships, the authors discuss naturological approaches to corporations and stakeholders. Connections with governance literature follow, emphasizing solutions in nature to age-old problems that contributed to recent abuses. The article closes with implications for socially responsible corporate governance.