Colony-size effects on task organization in the harvester ant Pogonomyrmex californicus

Holbrook, C. Tate; Eriksson, Ti H.; Overson, Rick P.; Gadau, Juergen; Fewell, Jennifer H.

doi:10.1007/s00040-013-0282-x

Cited by 21 publications

(24 citation statements)

References 62 publications

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“…These behaviours, in turn, can be influenced by group size. In ants, for example, allogrooming rates [15] and the relative performance of maintenance behaviours, such as waste removal [72], have been shown to increase with group size. A third possibility is that only a minority of the infectious agents in wild populations spread from host to host through social contact; instead, parasites and pathogens of wildlife may show a proportionally greater occurrence of routes involving faecal -oral transmission and vector transmission, and the strength of these transmission pathways may correlate more weakly with group size.…”

Section: Discussionmentioning

confidence: 99%

Infectious disease and group size: more than just a numbers game

Nunn

Jordán

McCabe

et al. 2015

Phil. Trans. R. Soc. B

155

163

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One contribution of 14 to a theme issue 'The sociality-health -fitness nexus in animal societies'. Increased risk of infectious disease is assumed to be a major cost of group living, yet empirical evidence for this effect is mixed. We studied whether larger social groups are more subdivided structurally. If so, the social subdivisions that form in larger groups may act as barriers to the spread of infection, weakening the association between group size and infectious disease. To investigate this 'social bottleneck' hypothesis, we examined the association between group size and four network structure metrics in 43 vertebrate and invertebrate species. We focused on metrics involving modularity, clustering, distance and centralization. In a meta-analysis of intraspecific variation in social networks, modularity showed positive associations with network size, with a weaker but still positive effect in cross-species analyses. Network distance also showed a positive association with group size when using intraspecific variation. We then used a theoretical model to explore the effects of subgrouping relative to other effects that influence disease spread in socially structured populations. Outbreaks reached higher prevalence when groups were larger, but subgrouping reduced prevalence. Subgrouping also acted as a 'brake' on disease spread between groups. We suggest research directions to understand the conditions under which larger groups become more subdivided, and to devise new metrics that account for subgrouping when investigating the links between sociality and infectious disease risk.

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Section: Discussionmentioning

confidence: 99%

Infectious disease and group size: more than just a numbers game

Nunn

Jordán

McCabe

et al. 2015

Phil. Trans. R. Soc. B

155

163

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“…The respirometry enclosures allow tracking of individual and colony-level locomotory behaviours, simultaneously with measurements of metabolic rate (electronic supplementary material, figures S1-S4). Previous studies suggest that work organization and performance change with colony size [57][58][59][60] and that work involving foraging, transport and inter-individual contact, requires increased metabolic expenditure [61][62][63]. Based on prior work demonstrating an effect of colony size on the distribution of walking speeds among individuals in P. californicus [1], we predicted that changes in colonial metabolic rates are partially due to changes in locomotory behaviour, with size-reduced colonies predicted to have relatively fewer inactive workers.…”

Section: Introductionmentioning

confidence: 95%

Differentiating causality and correlation in allometric scaling: ant colony size drives metabolic hypometry

et al. 2017

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Metabolic rates of individual animals and social insect colonies generally scale hypometrically, with mass-specific metabolic rates decreasing with increasing size. Although this allometry has wide ranging effects on social behaviour, ecology and evolution, its causes remain controversial. Because it is difficult to experimentally manipulate body size of organisms, most studies of metabolic scaling depend on correlative data, limiting their ability to determine causation. To overcome this limitation, we experimentally reduced the size of harvester ant colonies (Pogonomyrmex californicus) and quantified the consequent increase in mass-specific metabolic rates. Our results clearly demonstrate a causal relationship between colony size and hypometric changes in metabolic rate that could not be explained by changes in physical density. These findings provide evidence against prominent models arguing that the hypometric scaling of metabolic rate is primarily driven by constraints on resource delivery or surface area/volume ratios, because colonies were provided with excess food and colony size does not affect individual oxygen or nutrient transport. We found that larger colonies had lower median walking speeds and relatively more stationary ants and including walking speed as a variable in the mass-scaling allometry greatly reduced the amount of residual variation in the model, reinforcing the role of behaviour in metabolic allometry. Following the experimental size reduction, however, the proportion of stationary ants increased, demonstrating that variation in locomotory activity cannot solely explain hypometric scaling of metabolic rates in these colonies. Based on prior studies of this species, the increase in metabolic rate in sizereduced colonies could be due to increased anabolic processes associated with brood care and colony growth.

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“…There is also a trend towards stricter division of labour during social ontogeny, as social groups grow from a few individuals to many (Darchen, ; Holbrook et al , ). It is important to keep in mind that the influence of colony size on division of labour can rely on two mutually non‐exclusive processes (Holbrook et al , ). First, increased colony size can impact the degree of specialization without substantial changes at the individual level.…”

Section: Proximate Causes ‐ How Do Interindividual Differences Arise?mentioning

confidence: 99%

Interindividual variability in social insects – proximate causes and ultimate consequences

2013

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Individuals within social groups often show consistent differences in behaviour across time and context. Such interindividual differences and the evolutionary challenge they present have recently generated considerable interest. Social insects provide some of the most familiar and spectacular examples of social groups with large interindividual differences. Investigating these within-group differences has a long research tradition, and behavioural variability among the workers of a colony is increasingly regarded as fundamental for a key feature of social insects: division of labour. The goal of this review is to illustrate what we know about both the proximate mechanisms underlying behavioural variability among the workers of a colony and its ultimate consequences; and to highlight the many open questions in this research field. We begin by reviewing the literature on mechanisms that potentially introduce, maintain, and adjust the behavioural differentiation among workers. We highlight the fact that so far, most studies have focused on behavioural variability based on genetic variability, provided by e.g. multiple mating of the queen, while other mechanisms that may be responsible for the behavioural differentiation among workers have been largely neglected. These include maturational, nutritional and environmental influences. We further discuss how feedback provided by the social environment and learning and experience of adult workers provides potent and little-explored sources of differentiation. In a second part, we address what is known about the potential benefits and costs of increased behavioural variability within the workers of a colony. We argue that all studies documenting a benefit of variability so far have done so by manipulating genetic variability, and that a direct test of the effect of behavioural variability on colony productivity has yet to be provided. We emphasize that the costs associated with interindividual variability have been largely overlooked, and that a better knowledge of the cost/benefit balance of behavioural variability is crucial for our understanding of the evolution of the mechanisms underlying the social organization of insect societies. We conclude by highlighting what we believe to be promising but little-explored avenues for future research on how within-colony variability has evolved and is maintained. We emphasize the need for comparative studies and point out that, so far, most studies on interindividual variability have focused on variability in individual response thresholds, while the significance of variability in other parameters of individual response, such as probability and intensity of the response, has been largely overlooked. We propose that these parameters have important consequences for the colony response. Much more research is needed to understand if and how interindividual variability is modulated in order to benefit division of labour, homeostasis and ultimately colony fitness in social insects.

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Colony-size effects on task organization in the harvester ant Pogonomyrmex californicus

Cited by 21 publications

References 62 publications

Infectious disease and group size: more than just a numbers game

Infectious disease and group size: more than just a numbers game

Differentiating causality and correlation in allometric scaling: ant colony size drives metabolic hypometry

Interindividual variability in social insects – proximate causes and ultimate consequences

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