A fundamental goal of sociobiology is to explain how complex social behaviour evolves¹, especially in social insects, the exemplars of social living. Although still the subject of much controversy², recent theoretical explanations have focused on the evolutionary origins of worker behaviour (assistance from daughters that remain in the nest and help their mother to reproduce) through expression of maternal care behaviour towards siblings^{3, 4}. A key prediction of this evolutionary model is that traits involved in maternal care have been co-opted through heterochronous expression of maternal genes⁵ to result in sib-care, the hallmark of highly evolved social life in insects⁶. A coupling of maternal behaviour to reproductive status evolved in solitary insects, and was a ready substrate for the evolution of worker-containing societies^{3, 4, 7, 8}. Here we show that division of foraging labour among worker honey bees (Apis mellifera) is linked to the reproductive status of facultatively sterile females. We thereby identify the evolutionary origin of a widely expressed social-insect behavioural syndrome^{1, 5, 7, 9}, and provide a direct demonstration of how variation in maternal reproductive traits gives rise to complex social behaviour in non-reproductive helpers.

1. Arizona State University, School of Life Sciences, Tempe, Arizona 85287, USA
2. University of Life Sciences, Department of Animal and Aquacultural Sciences, 1432 Aas, Norway
3. University of California, Department of Entomology, Davis, California 95616, USA

Correspondence to: Gro V. Amdam^1,2Robert E. Page, Jr¹ Correspondence and requests for materials should be addressed to G.V.A. (Email: Gro.Amdam@asu.edu) or R.E.P. (Email: Robert.Page@asu.edu).

Received 10 September 2005 | Accepted 19 October 2005

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