Evolution

Nature over Nurture

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Science  10 May 2002:
Vol. 296, Issue 5570, pp. 985
DOI: 10.1126/science.296.5570.985a

Social insect colonies are divided into different castes with different functions. The environmental determination of caste division has been argued to be essential to the evolution of true sociality in insects. But Volny and Gordon have discovered that the caste system of the red harvester ant is genetically determined. A single queen founds each red harvester ant colony. During the 15 to 20 years of her life, this queen will only use the sperm from her original matings to produce all of the colony's worker and reproductive castes. Sterile workers are the offspring of parents from different lineages, whereas reproductives stem from parents of the same lineage. A viable colony needs both castes, and so to establish a colony the queen must mate with males from more than one lineage. This means that the two lineages will evolve separately by genetic drift while having to remain codependent. A further problem with this type of genetically determined caste system is that it restricts the ability of the colony to change the ratio of workers and reproductives in response to seasonal changes in resources.—CA

Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.092066699 (2002).

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