Eamonn B. Mallon

Individual and collective decision-making during nest site selection by the ant Leptothorax albipennis

Abstract. Social insect colonies possess remarkable abilities to select the best among several courses of action. In populous societies with highly efficient recruitment behaviour, decision-making is distributed across many individuals, each acting on limited local information with appropriate decision rules. To investigate the degree to which small societies with less efficient recruitment can also employ distributed decision-making, we studied nest site selection in Leptothorax albipennis. Colonies were found to make sophisticated choices, taking into account not only the intrinsic qualities of each site, but also its value relative to the available options. In choices between two sites, individual ants were able to visit both sites, compare them and choose the better one. However, most ants encountered only one site in the course of an emigration. These poorly informed ants also contributed to the colonys decision, because their probability of initiating recruitment to a site depended on its quality. This led to shorter latencies between discovery and recruitment to a superior site, and so created greater amplification via positive feedback of the population at the better site. In short, these small colonies make use of a distributed mechanism of information processing, but also take advantage of direct decision-making by well-informed individuals. The latter feature may in part stem from the limitations of their social structure, but may also reflect the stringent demand for unanimous decisions by house-hunting colonies of any size.

An agent-based model of collective nest choice by the ant Temnothorax albipennis

Colonies of the ant Temnothorax (formerly Leptothorax) albipennis can collectively choose the best of several nest sites, even when many of the active ants who organize the move visit only one site ...

Ants estimate area using Buffon's needle

We show for the first time, to our knowledge, that ants can measure the size of potential nest sites. Nest size assessment is by individual scouts. Such scouts always make more than one visit to a potential nest before initiating an emigration of their nest mates and they deploy individual–specific trails within the potential new nest on their first visit. We test three alternative hypotheses for the way in which scouts might measure nests. Experiments indicated that individual scouts use the intersection frequency between their own paths to assess nest areas. These results are consistent with ants using a ‘Buffons needle algorithm’ to assess nest areas.

Insect psychoneuroimmunology: Immune response reduces learning in protein starved bumblebees (Bombus terrestris)

It is well established in vertebrates that there are many intricate interactions between the immune system and the nervous system. Here, we present behavioural evidence indicating a link between the immune system and the nervous system in insects. We show that otherwise non-infected bumblebees whose immune systems were challenged by a non-pathogenic immunogenic elicitor (lipopolysaccharide) have reduced abilities to learn or recall a memory in a classical conditioning paradigm. There is evidence that protein is intricately involved as this immune induced reduction in memory only becomes apparent after the bees are deprived of pollen (their only protein sources).

Differential Expression of Immune Defences Is Associated with Specific Host-Parasite Interactions in Insects

Recent ecological studies in invertebrates show that the outcome of an infection is dependent on the specific pairing of host and parasite. Such specificity contrasts the long-held view that invertebrate innate immunity depends on a broad-spectrum recognition system. An important question is whether this specificity is due to the immune response rather than some other interplay between host and parasite genotypes. By measuring the expression of putative bumblebee homologues of antimicrobial peptides in response to infection by their gut trypanosome Crithidia bombi, we demonstrate that expression differences are associated with the specific interactions.

Methylation and worker reproduction in the bumble-bee (Bombus terrestris)

Insects are at the dawn of an epigenetics era. Numerous social insect species have been found to possess a functioning methylation system, previously not thought to exist in insects. Methylation, an epigenetic tag, may be vital for the sociality and division of labour for which social insects are renowned. In the bumble-bee Bombus terrestris, we found methylation differences between the genomes of queenless reproductive workers and queenless non-reproductive workers. In a follow up experiment, queenless workers whose genomes had experimentally altered methylation were more aggressive and more likely to develop ovaries compared with control queenless workers. This shows methylation is important in this highly plastic reproductive division of labour. Methylation is an epigenetic tag for genomic imprinting (GI). It is intriguing that the main theory to explain the evolution of GI predicts that GI should be important in this worker reproduction behaviour.

Pathways to immunity : temporal dynamics of the bumblebee (Bombus terrestris) immune response against a trypanosomal gut parasite

Immune response dynamics in insects from natural host−parasite associations are poorly understood, despite accumulating evidence of ecological immune phenomena in these systems. Using a gene discovery approach, we have identified genes relating to signalling, enzymatic processes and respiration that were up‐regulated in the bumblebee, Bombus terrestris, during infection with the trypanosomatid parasite, Crithidia bombi. In addition, we have mapped dynamic changes in the temporal expression of these genes and three candidate antimicrobial peptide (AMP) immune genes, Abaecin, Defensin and Hymenoptaecin, from 1 to 24 h after C. bombi infection. We show that dynamic changes in expression occur for individual genes at distinct phases of the immune response to C. bombi that correspond to early, intermediate and late stages of infection.

Immune response impairs learning in free-flying bumble-bees

Parasites can influence different host behaviours including foraging, mate choice and predator avoidance. Several recent papers have shown reduced learning abilities in infected insects. However, it is difficult to separate the effects of the immune response from the direct effects of the parasite. Using a free-flying learning paradigm, this paper shows that learning performance is impaired in bumble-bees (Bombus terrestris) that are not infected but whose immune system is stimulated non-pathogenically. This demonstrates that before it is assumed that a parasite has a direct effect on a hosts behaviour, the effect of the immune response stimulated by the parasite must first be quantified.

An immune response in the bumblebee, Bombus terrestris leads to increased food consumption

BackgroundThe concept of a costly immune system that must be traded off against other important physiological systems is fundamental to the burgeoning field of ecological immunity. Bumblebees have become one of the central models in this field. Although previous work has demonstrated costs of immunity in numerous life history traits, estimates of the more direct costs of bumblebee immunity have yet to be made.ResultsHere we show a 7.5% increase in energy consumption in response to non-pathogenic immune stimulation.ConclusionThis increase in energy consumption along with other results suggests that immunity is one of the most important physiological systems, with other systems being sacrificed for its continuing efficiency. This increased consumption and maintained activity contrasts with the sickness-induced anorexia and reduced activity found in vertebrates.

Antimicrobial peptides play a functional role in bumblebee anti-trypanosome defense

Bumblebees, amongst the most important of pollinators, are under enormous population pressures. One of these is disease. The bumblebee and its gut trypanosome Crithidia bombi are one of the fundamental models of ecological immunology. Although there is previous evidence of increased immune gene expression upon Crithidia infection, recent work has focussed on the bumblebees gut microbiota. Here, by knocking down gene expression using RNAi, we show for the first time that antimicrobial peptides (AMPs) have a functional role in anti-Crithidia defense.