Haplodiploidy and the Evolution of Eusociality: Split Sex Ratios
vol. 179, no. 2 the american naturalist february 2012 Haplodiploidy and the Evolution of Eusociality: Split Sex Ratios Andy Gardner,1,2,* Joa˜o Alpedrinha,1,3 and Stuart A. West1 1. Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, United Kingdom; 2. Balliol College, University of Oxford, Broad Street, Oxford OX1 3BJ, United Kingdom; 3. Instituto Gulbenkian de Cieˆncia, Apartado 14, PT-2781-901 Oeiras, Portugal Submitted June 29, 2011; Accepted October 20, 2011; Electronically published December 21, 2011 the rearing of an extra sister to provisioning a cell for a daugh- abstract: It is generally accepted that from a theoretical perspec- ter of her own. (Hamilton 1964, p. 28–29) tive, haplodiploidy should facilitate the evolution of eusociality. How- ever, the “haplodiploidy hypothesis” rests on theoretical arguments The eusocial societies are dominated by species with hap- that were made before recent advances in our empirical understand- lodiploid genetics, especially the social Hymenoptera—the ing of sex allocation and the route by which eusociality evolved. Here ants, bees, and wasps. Although eusociality is also found we show that several possible promoters of the haplodiploidy effect would have been unimportant on the route to eusociality, because in diploid species, such as termites, its distribution is sig- they involve traits that evolved only after eusociality had become nificantly biased toward haplodiploid families (Crozier established. We then focus on two biological mechanisms that could 2008). Hamilton (1964, 1972) suggested that this was be- have played a role: split sex ratios as a result of either queen virginity cause haplodiploidy facilitates the evolution of altruistic or queen replacement.
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