Individual error correction drives responsive self-assembly of army ant scaffolds

Army ants take the stage

The effect of Eciton burchelli army ants (Hymenoptera: Formicidae) on leaf-litter arthropods was studied at Finca La Selva, Costa Rica. Analyses of leaf-litter samples indicated that both arthropod abundance and the number of taxa were reduced following the passage of foraging army ant swarms. Many of the arthropods in the path of an ant swarm escape; the escape tactics that we observed are presented. Full evaluation of the impact of army ant swarms on the arthropod community requires quantification of the rates of capture by both the army ants and the associated swarm-following birds, and of the rate of parasitization by flies that follow the ant swarms. ECITON BURCHELLI (FORMICIDAE: ECITONINAE) IS A COMMON, swarm-raiding army ant of the neotropical forests; its foraging swarms cover broad area and capture wide diversity of arthropods. Because colonies of E. burchelli have large daily intake of food, they presumably have substantial impact on litter arthropods in the areas in which they forage (Wilson 1971, Rettenmeyer et al. 1983). Their effectiveness in prey capture is not clear, however. In an early publication, Schneirla commented that they clear insect life rather completely from terrain over which they pass (1934, based partly on observations of Bates 1863 and Belt 1874). More recently, Schneirla (1949, 1971) and Rettenmeyer (1963) estimated that 30-50 percent of the litter arthropods escape E. burchelli swarms. In study of tropical leaf-litter arthropods, Williams (1941) analyzed the fauna from two plots the day after they were raided by army ants Labidus praedator and indicated that arthropod densities were reduced to a minimum. Franks (1982a, b; Franks & Bossert 1983; Franks & Fletcher 1983) has studied the effects of E. burchelli ants on leaf-litter communities in detail; his results will be referenced below when appropriate. In this study, we investigated the impact of foraging E. burchelli by measuring the densities of leaf-litter arthropods before and after the passage of army ant

Myrmecophiles

Eciton burchellii is a Neotropical army ant that consumes a variety of arthropods captured during swarm raids. Wasp larvae and pupae provide an important food source for E. burchellii, and this ant species is thought to be a major predator on immature wasps in many Neotropical areas. Some birds also prey on wasp brood. Numerous bird species regularly follow E. burchellii swarms but are thought to typically avoid eating army ants. Rather, the birds feed on the arthropods that the ant swarms flush from the leaf litter. I report observations of ant-following birds, the Gray-headed Tanager Eucometis penicillata and the Flame-colored Tanager Piranga bidentata consuming E. burchellii workers that were carrying Polistinae wasp larvae and pupae. It has been suggested that ant-following birds may impose a cost to army ants by consuming arthropods and competing with ants for food resources. Also, it has been speculated that army ants emigrate at night to avoid the loss of their brood to birds, but lack of ...

The combination of haplodiploidy, complementary sex determination and eusociality constrains the effective population size (Ne) of social Hymenoptera far more than in any other insect group. Additional limitations onNeoccur in army ants since they have wingless queens and colony fission, both of which are factors causing restricted maternal gene flow and high population viscosity. Therefore, winged army ant males gain a particular significance to ensure dispersal, facilitate gene flow and avoid inbreeding. Based on population genetic analyses with microsatellite markers, we studied a population of the Neotropical army antEciton burchellii, finding a high level of heterozygosity, weak population differentiation and no evidence for inbreeding. Moreover, by using sibship reconstruction analyses, we quantified the actual number of male contributing colonies represented in a queen's mate sample, demonstrating that, through extreme multiple mating, the queens are able to sample the genes of males from up to ten different colonies, usually located within an approximate radius of 1 km. We finally correlated the individual mating success of each male contributing colony with the relative siring success of individual males and found a significant colony‐dependent male fitness component. Our results imply that the dispersal and mating system of these army ants seem to enhance gene flow and minimise the deleterious effects associated with small effective population size.

Army ants provide nourishment to a large variety of animals. This includes birds that feed on animals flushed out by army ant raids, symbiotic arthropods that consume the ants' prey or their brood, and other arthropods that scavenge on army ant refuse deposits. The latter have not received much attention, and the few published studies lack detailed species identifications. Here we provide a first systematic inventory of the beetle fauna associated with refuse deposits of Eciton army ants, with a focus on Eciton burchellii. We collected 8364 adult beetles, 511 larvae, and 24 eggs from 34 deposits at La Selva Biological Station, Costa Rica. We used a combination of DNA barcoding and morphology to identify a subset of 436 specimens to species level. The samples included several new species, and we here formally describe two water scavenger beetles (Hydrophilidae). Refuse deposits harbored a diverse beetle fauna. The identified subset consisted of 91 beetle species from 12 families, with rove beetles being the most abundant and diverse visitors. Of the 85 species found with E. burchellii, 50 species were collected from only one or two refuse deposits. Conversely, seven species were found in 10 or more refuse deposits, indicating a certain level of habitat specialization. We matched adults and immatures for 22 beetle species via DNA barcodes, demonstrating that army ant middens also serve as a beetle nursery. The present survey highlights the significant ecological function of army ants as promoters of biodiversity and their status as keystone species in tropical rainforests.

Inhibited dispersal, leading to reduced gene flow, threatens populations with inbreeding depression and local extinction. Fragmentation may be especially detrimental to social insects because inhibited gene flow has important consequences for cooperation and competition within and among colonies. Army ants have winged males and permanently wingless queens; these traits imply male-biased dispersal. However, army ant colonies are obligately nomadic and have the potential to traverse landscapes. Eciton burchellii, the most regularly nomadic army ant, is a forest interior species: colony raiding activities are limited in the absence of forest cover. To examine whether nomadism and landscape (forest clearing and elevation) affect population genetic structure in a montane E.burchellii population, we reconstructed queen and male genotypes from 25 colonies at seven polymorphic microsatellite loci. Pairwise genetic distances among individuals were compared to pairwise geographical and resistance distances using regressions with permutations, partial Mantel tests and random forests analyses. Although there was no significant spatial genetic structure in queens or males in montane forest, dispersal may be male-biased. We found significant isolation by landscape resistance for queens based on land cover (forest clearing), but not on elevation. Summed colony emigrations over the lifetime of the queen may contribute to gene flow in this species and forest clearing impedes these movements and subsequent gene dispersal. Further forest cover removal may increasingly inhibit Eciton burchellii colony dispersal. We recommend maintaining habitat connectivity in tropical forests to promote population persistence for this keystone species.

This article describes a test of Karasek's Job Demand-Control (JD-C) Model using both group and individual level assessments of job characteristics. By group assessments, we mean aggregated individual data. A random sample from general hospitals and nursing homes included 16 institutions, 64 units, and 1489 health care workers (82% response). Because of the hierarchically nested data structure (i.e., institutions, units, and individuals) the research questions and hypothesis were tested in multilevel regression analyses (VARCL). The results revealed both group level and individual level effects with regard to psychological outcomes, and stressed the usefulness of multilevel techniques. Karasek's JID-C Model was partly confirmed by finding two interaction effects at group level and at individual level with regard to job satisfaction and work motivation, respectively. The discussion focuses on theoretical, methodological, and practical implications of multilevel modeling with respect to the JD-C Model.

New World army ants (Ecitoninae) are nomadic group-predators that are widely thought to have a substantial impact on their prey. Nevertheless, quantitative data on prey intake by army ants is scarce and mostly limited to chance encounters. Here, I quantify the prey intake of the army ant Eciton hamatum at the contrasting scales of raid, colony (sum of simultaneous raids), and population. Like most army ants, E. hamatum conducts narrow ‘column raids’ and has a specialized diet of ant prey. I show that individual raids often had periods of no prey intake, and raid intake rates, calculated in g/min, differed significantly among colonies. Moreover, neither mean nor peak raid intake rates were correlated with colony size. Similarly, colony intake rates differed significantly among colonies, and mean colony intake rates were not correlated with colony size. However, mean colony intake rates were significantly higher than mean raid intake rates, and peak colony intake rate was correlated with colony size. Having multiple raids thus improves colony-level intake rates, and larger colonies can harvest more prey per unit time. Mean colony intake rate across colonies was 0.067 g/min dry weight and mean daily colony intake was calculated at 38.2 g. This intake is comparable to that of Eciton burchellii, which has a more generalized diet and conducts spectacular ‘swarm raids’ that are seen as having a greater impact on prey than column raids. Population size on Barro Colorado Island, Panama, was estimated to be 57 colonies, which extrapolates to a daily population intake of nearly 2 kg of prey dry weight, or 120 g/km2. Broadly, these findings demonstrate that column raiding army ants experience considerable variation in prey intake for individual raids, but can still achieve notable impact at the larger scales of colony and population. Furthermore, they challenge the idea that swarm-raiding species necessarily have greater intake and thus impact on prey. Instead, I suggest that conducting multiple column raids may be a strategy that allows for comparable intake from a more specialized diet.

In a self-organizing particle system, an abstraction of programmable matter, simple computational elements called particles with limited memory and communication self-organize to solve system-wide problems of movement, coordination, and configuration. In this paper, we consider a stochastic, distributed, local, asynchronous algorithm for "shortcut bridging", in which particles self-assemble bridges over gaps that simultaneously balance minimizing the length and cost of the bridge. Army ants of the genus Eciton have been observed exhibiting a similar behavior in their foraging trails, dynamically adjusting their bridges to satisfy an efficiency trade-off using local interactions. Using techniques from Markov chain analysis, we rigorously analyze our algorithm, show it achieves a near-optimal balance between the competing factors of path length and bridge cost, and prove that it exhibits a dependence on the angle of the gap being "shortcut" similar to that of the ant bridges. We also present simulation results that qualitatively compare our algorithm with the army ant bridging behavior. Our work gives a plausible explanation of how convergence to globally optimal configurations can be achieved via local interactions by simple organisms (e.g., ants) with some limited computational power and access to random bits. The proposed algorithm also demonstrates the robustness of the stochastic approach to algorithms for programmable matter, as it is a surprisingly simple extension of our previous stochastic algorithm for compression.

As possibly two of the last true naturalists, Carl Rettenmeyer and his wife Marian dedicated their lives to the study of army ants and their associates. Over the course of 55 years, the Rettenmeyers went on numerous field trips mainly to the Central American tropics and analyzed hundreds of self-collected samples and those sent by a multitude of other scientists, who were inspired by Carl’s enthusiasm. It comes as no surprise that Carl Rettenmeyer became the world’s leading expert on army ant associates. This paper, which the Rettenmeyers nearly completed before Carl’s death in 2009, gives the first comprehensive list of animals known to be found in the company of a single army ant species: Eciton burchellii. The 557 recorded associates range from birds to insects and mites and comprise the largest described animal association centering around one particular species. Although some of these associates may be opportunistic encounters, we are confident that approximately 300 of the recorded species depend on the ants, at least in part, for their existence. The extinction of E. burchellii from any habitat over its vast area of distribution is likely to cause the extinction of numerous associated animals at that site. This overview will hopefully inspire researchers throughout the world to follow in the Rettenmeyers’ footsteps and continue the investigation of army ants and their associates.

Foraging army ants face a problem general to many animals—how best to confront resource depletion and environmental heterogeneity. Army ants have presumably evolved a nomadic lifestyle as a way to minimize re-exploitation of previously foraged areas. However, this solution creates a challenge for an army ant colony: foraging by this colony and others creates a shifting landscape of food resources, where colonies should theoretically avoid their own previous foraging paths as well as those of other colonies. Here, we examine how colonies exploit this resource mosaic, using some of the optimality arguments first proposed and tested by Franks and Fletcher (1983), but with much larger data sets in a new location in SW Amazonia. Our data supported Franks and Fletcher’s (1983) model for systematic avoidance of raided areas during the statary phase, as well as a hypothesis of distance optimization between successive statary bivouacs. We also test and find significant evidence that foraging raids turn in opposite directions from the previous day’s directional angles more frequently than what would be expected if turning angles were distributed at random, which acts to move a colony away from recently exploited areas. This implies that colonies follow a straighter line path during the nomadic phase as opposed to a curved one, which acts to maximize distance between statary bivouacs. In addition to intra-colony movement optimization, we examine evidence for inter-colony avoidance from more than 330 colony emigrations and suggest that colony-specific pheromones are not necessarily repulsive to other colonies. Lastly, we compare our results with those of similar studies carried out at Barro Colorado Island (BCI), Panama. Despite a higher density of army ants in the SW Amazon region, colonies spend less time emigrating than their counterparts at BCI, which suggests a higher prey density in SW Amazonia.

The evolution of mass raiding has allowed army ants to become dominant arthropod predators in the tropics. Although a century of research has led to many discoveries about behavioural, morphological and physiological adaptations in army ants, almost nothing is known about the molecular basis of army ant biology. Here we report the genome of the iconic New World army ant Eciton burchellii, and show that it is unusually compact, with a reduced gene complement relative to other ants. In contrast to this overall reduction, a particular gene subfamily (9‐exon ORs) expressed predominantly in female antennae is expanded. This subfamily has previously been linked to the recognition of hydrocarbons, key olfactory cues used in insect communication and prey discrimination. Confocal microscopy of the brain showed a corresponding expansion in a putative hydrocarbon response centre within the antennal lobe, while scanning electron microscopy of the antenna revealed a particularly high density of hydrocarbon‐sensitive sensory hairs. E. burchellii shares these features with its predatory and more cryptic relative, the clonal raider ant. By integrating genomic, transcriptomic and anatomical analyses in a comparative context, our work thus provides evidence that army ants and their relatives possess a suite of modifications in the chemosensory system that may be involved in behavioural coordination and prey selection during social predation. It also lays the groundwork for future studies of army ant biology at the molecular level.

The army ant Eciton burchellii boasts more animal associates than any other animal species yet described, but the relationship between army ants and other ant species has only been studied in the context of predation. The waste deposits (middens) of army ant colonies are nitrogen‐rich, a potentially high‐value nutrient source for leaflitter arthropods. We explored this bottom‐up role of army ant middens in the context of tropical ant communities. Our three main questions were the followings: (1) Which ant species forage on army‐ant middens? (2) How does the bi‐phasic life cycle of army ant colonies (affecting midden size, persistence, and abundance) affect which and how many ant species a midden boasts? (3) How do the ants that forage on army ant middens differ across elevations? Across 39 bivouacs, we found 36 species of ants foraging on army ant middens. These included highly predatory ants, nitrogen‐limited arboreal ants, and fungus‐farming ants. Per‐midden richness was significantly lower for the usually smaller middens deposited during the nomadic phase and was higher for the typically larger middens deposited during the statary phase. Per‐midden richness was not significantly different across elevations, but there was far greater species turnover across elevations than across phases within the same elevational site. Our results suggest that army ant middens are an important resource for a wide variety of tropical ants, informing a better understanding of the complex network of associations revolving around this keystone species.Abstract in Spanish is available with online material

In this note we describe a raid by army ants (Eciton burchelli Westwood) on a colony of tropical swarm-founding wasps (Agelaia yepocapa Richards). The general features of such raids have been discussed elsewhere (Jeanne 1970, Naumann 1975, Young 1979). Army ants are a major predation force on social wasp colonies in many Neotropical areas (Chadab 19 79a, Jeanne 1975), and features of swarm-founding wasp behaviour indicate strong selection for dealing with army ant predation (Chadab 19 79b, Jeanne 1975). The raid described here involved a number of behavioural responses of the wasps to the ant attack which have not been reported before, and occurred at an unusually high elevation. The raid took place next to the dirt road leading to the Monteverde Cloud Forest Preserve in Puntarenas Province, Costa Rica. The wasp nest was located 4 m above the ground in a trunk cavity of a large (about 0.7 m DBH) broadleaf tree, several kilometres downhill from the Preserve headquarters. The surrounding habitat is a mixture of disturbed forest and pasture, at an elevation of about 1100 m. This is near the upper elevational limit for E. burchelli in the area (William Haber, pers. comm.) We first noticed the attack on 27 July 1988 late in the morning, but local residents claimed it had begun the previous afternoon. Army ants were entering the wasp nest cavity and extracting wasp brood (larvae and pupae) when we arrived, and continued to do so during our last observation at 1500 h that afternoon. The raid spanned a period of at least 24 h though it is uncertain whether it had continued through the night, when army ants usually bivouac (Franks 1989). The wasps were identified as Agelaia yepocapa (formerly Stelopolybia yepocapa). This is the first record of an A. yepocapa nesting site; like most