Lanchester's models of attrition describe casualty rates during battles between groups as functions of the numbers of individuals and their fighting abilities. Originally developed to describe human warfare, Lanchester's square law has been hypothesized to apply broadly to social animals as well, with important consequences for their aggressive behaviour and social structure. According to the square law, the fighting ability of a group is proportional to the square of the number of individuals, but rises only linearly with fighting ability of individuals within the group. By analyzing mortality rates of fire ants (Solenopsis invicta) fighting in different numerical ratios, we provide the first quantitative test of Lanchester's model for a nonhuman animal. Casualty rates of fire ants were not consistent with the square law; instead, group fighting ability was an approximately linear function of group size. This implies that the relative numbers of casualties incurred by two fighting groups are not strongly affected by relative group sizes and that battles do not disproportionately favour group size over individual prowess.

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Inflammation is often accompanied by robust angiogenesis. Vascular endothelial cells (ECs) express erbB receptors and their ligand, neuregulin-1, and can respond to neuregulin by proliferation and angiogenesis. We hypothesized that some growth factor-like responses of ECs to inflammatory cytokines can be explained by cleavage of transmembrane neuregulin with subsequent release of its extracellular epidermal growth factor-like-containing domain and autocrine activation. Using a model of cultured human ECs, we found that interleukin-6 or interferon-gamma causes rapid cleavage and release of transmembrane neuregulin. Inhibitors of metalloproteinases abolish this effect. The addition of an inhibitor of tumor necrosis factor-alpha converting enzyme (TACE) blocks cytokine-induced neuregulin release. Silencing of TACE expression increases the amount of basal proneuregulin present in ECs but does not block neuregulin release in response to phorbol myristate acetate (PMA), suggesting that other proteinases are responsible for mediating protein kinase C-dependent cleavage. Cytokines capable of inducing neuregulin cleavage stimulated ERK activation and in vitro angiogenesis (Matrigel cord formation). This effect is blocked by inhibitors that block neuregulin cleavage, erbB protein tyrosine kinase inhibitors, or antineuregulin-neutralizing antibodies. Cytokine-activated metalloproteinase cleavage of neuregulin may play an important role in autocrine activation of EC signaling pathways, contributing to key biological effects, perhaps including inflammation-associated angiogenesis.

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The desert harvester ant (Veromessor pergandei) employs a mixture of social and individual navigational strategies at separate stages of their foraging trip. Individuals leave the nest along a pheromone-based column, travelling 3-40 m before spreading out to forage individually in a fan. Foragers use path integration while in this fan, accumulating a direction and distance estimate (vector) to return to the end of the column (column head), yet foragers' potential use of path integration in the pheromone-based column is less understood. Here we show foragers rely on path integration both in the foraging fan and while in the column to return to the nest, using separate vectors depending on their current foraging stage in the fan or column. Returning foragers displaced while in the fan oriented and travelled to the column head location while those displaced after reaching the column travel in the nest direction, signifying the maintenance of a two-vector system with separate fan and column vectors directing a forager to two separate spatial locations. Interestingly, the trail pheromone and not the surrounding terrestrial cues mediate use of these distinct vectors, as fan foragers briefly exposed to the pheromone cues of the column in isolation altered their paths to a combination of the fan and column vectors. The pheromone acts as a contextual cue triggering both the retrieval of the column-vector memory and its integration with the forager's current fan-vector.

Foraging ants use multiple navigational strategies, including path integration and visual panorama cues, which are used simultaneously and weighted based upon context, the environment and the species' sensory ecology. In particular, the amount of visual clutter in the habitat predicts the weighting given to the forager's path integrator and surrounding panorama cues. Here, we characterize the individual cue use and cue weighting of the Sonoran Desert ant, Novomessor cockerelli, by testing foragers after local and distant displacement. Foragers attend to both a path-integration-based vector and the surrounding panorama to navigate, on and off foraging routes. When both cues were present, foragers initially oriented to their path integrator alone, yet weighting was dynamic, with foragers abandoning the vector and switching to panorama-based navigation after a few meters. If displaced to unfamiliar locations, experienced foragers travelled almost their full homeward vector (~85%) before the onset of search. Through panorama analysis, we show views acquired on-route provide sufficient information for orientation over only short distances, with rapid parallel decreases in panorama similarity and navigational performance after even small local displacements. These findings are consistent with heavy path integrator weighting over the panorama when the local habitat contains few prominent terrestrial cues.

We combined behavioral analyses in the laboratory and field to investigate chemical communication in the formation of foraging columns in two Nearctic seed harvesting ants, Messor pergandei and Messor andrei. We demonstrate that both species use poison gland secretions to lay recruitment trails. In M. pergandei, the recruitment effect of the poison gland is enhanced by adding pygidial gland secretions. The poison glands of both species contain 1-phenyl ethanol. Minute quantities (3 μl of a 0.1 ppm solution) of 1-phenyl ethanol drawn out along a 40 cm long trail released trail following behavior in M. pergandei, while M. andrei required higher concentrations (0.5-1 ppm). Messor pergandei workers showed weak trail following to 5 ppm trails of the pyrazines 2,5-dimethylpyrazine and 2,3,5-trimethylpyrazine, whereas M. andrei workers showed no behavioral response. Minute quantities of pyrazines were detected in M. pergandei but not in M. andrei poison glands using single ion monitoring gas chromatography-mass spectrometry.