Patterns of split sex ratio in ants have multiple evolutionary causes based on different within-colony conflicts

Institute of Evolutionary Biology, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, UK.
Biology letters (Impact Factor: 3.25). 06/2009; 5(5):713-6. DOI: 10.1098/rsbl.2009.0295
Source: PubMed


Split sex ratio-a pattern where colonies within a population specialize in either male or queen production-is a widespread phenomenon in ants and other social Hymenoptera. It has often been attributed to variation in colony kin structure, which affects the degree of queen-worker conflict over optimal sex allocation. However, recent findings suggest that split sex ratio is a more diverse phenomenon, which can evolve for multiple reasons. Here, we provide an overview of the main conditions favouring split sex ratio. We show that each split sex-ratio type arises due to a different combination of factors determining colony kin structure, queen or worker control over sex ratio and the type of conflict between colony members.

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    • "As a consequence, the breeding system imposes selection pressures on sex bias strategies in queen(s) and/or workers (Trivers and Hare 1976; Pamilo 1991; Chapuisat and Keller 1999). One of the most interesting and well-studied of such phenomena in ants is the existence of so-called " split " or bimodal sex ratios, where some colonies produce mainly female sexuals and others produce mainly male sexuals (Boomsma and Grafen 1990, 1991; Kümmerli and Keller 2009). "
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