Colonylevel Investment

Investment in Growth and Maintenance versus Reproduction

One of the major challenges that faces growing organisms is the developmental decision of how many resources to invest in growth and how many to invest in reproduction. Insect colonies can be treated as organisms in this sense, since each colony must decide how much it will invest in different castes (i.e., in workers vs reproductives). To the extent that colonies are reproductive units, optimality theory predicts that natural selection will favor colonies that allocate their limited resources efficiently into different castes. Many insect societies segregate the production of workers (early in colony development) from the production of new queens and males (later in colony development).

Worker Caste Ratios

Insect colonies appear to behave in an adaptive manner by adjusting their worker caste ratios to meet current colony needs. Production of different worker castes reflects a trade-off between the costs and benefits of producing and maintaining workers of different kinds. As ant colonies with morphologically specialized workers grow in size, their amount of investment in large-bodied workers increases, and many eusocial insects produce tiny nanitic workers early in colony development. Colonies of the ant Pheidole pallidula increase their rate of production of soldiers when exposed to potential competitors. Similar colony flexibility is apparent in age—caste distributions. In honey bees and paper wasps, if the level-of-colony need for foragers changes, some workers accelerate or reverse their behavioral development, performing the age-atypical tasks that are in greatest demand. Identifying the mechanisms that link individuals' developmental plasticity with the level of colony need remains as a central challenge in the study of caste.

See Also the Following Articles

Colonies • Division of Labor • Hymenoptera • Isoptera • Juvenile Hormone • Sociality

Further Reading

Evans, J. D., and Wheeler, D. E. (2001). Gene expression and the evolution of insect polyphenisms. Bioessays 23, 62—68. Holldobler, B., and Wilson, E. O. (1990). "The Ants." Harvard University

Press, Cambridge, MA. Hunt, J. H. (1994). Nourishment and social evolution in wasps sensu lato. In "Nourishment and Evolution in Insect Societies" (J. H. Hunt and C. A. Nalepa, eds.), pp. 221-254. Westview Press, Boulder, CO. O'Donnell, S. (1998). Reproductive caste determination in eusocial wasps

(Hymenoptera: Vespidae). Annu. Rev. Entomol. 43, 323-346. Oster, G. W., and Wilson, E. O. (1978). "Caste and Ecology in the Social

Insects." Princeton University Press, Princeton, NJ. Peters, C., and Ito, F. (2001). Colony dispersal and the evolution of queen morphology in social Hymenoptera. Annu. Rev. Entomol. 46, 601-630.

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