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Tug-of-war over reproduction in a social bee


One of the main transitions in evolution is the shift from solitary organisms to societies with reproductive division of labour1,2. Understanding social evolution requires us to determine how ecological, social and genetic factors jointly influence group stability and partitioning of reproduction between group members3,4,5,6,7,8. Here we test the role of the three key factors predicted to influence social evolution by experimentally manipulating them in a social allodapine bee. We show that increased relatedness between nestmates results in more even reproduction among group members and a greater productivity per individual. By contrast, the degree of reproductive skew is not influenced by the opportunity for solitary breeding or by the potential benefits of cooperation. Relatedness also has a positive effect on group stability and overall productivity. These findings are in line with predictions of the tug-of-war models, in which the degree of reproductive division of labour is determined primarily by selfish competition between group members. The alternative view, where the degree of reproductive skew is the outcome of a social contract between potential breeders, was not supported by the data.

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Figure 1: Reproductive skew in nests of the high- and low-relatedness treatment, and in unmanipulated control nests.
Figure 2: Correlation between relatedness and reproductive skew across all nests.
Figure 3: Reproductive skew in treatments with high or low nesting substrate availability.
Figure 4: Reproductive skew in treatments with rich and poor floral resources (high and low k, respectively).


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We thank C. Roger, P. Jordan and G. Deppierraz for help in genotyping, N. DiMarco for extractions, M. P. Schwarz for methodological advice, A. Marazzi for statistical assistance, J. Zammit, C. van der Muren, E. Geertsema and T. Taraldsrud for help in setting up field experiments, and R. Hammond, M. Chapuisat, P. Christe, S. Helms Cahan, K. Parker, D. Queller and F. Ratnieks for comments on the manuscript.

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Correspondence to Philipp Langer or Laurent Keller.

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Supplementary information

Supplementary Methods

Describes additional relatedness analyses in the experiments for solitary nesting constraints (x) and for relative goup productivity (k), as well as details for genetic analyses and reproductive skew calculations. (PDF 17 kb)

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Langer, P., Hogendoorn, K. & Keller, L. Tug-of-war over reproduction in a social bee. Nature 428, 844–847 (2004).

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