On the relationship between aggression and reproduction in pairs of orphaned worker bumblebees ( Bombus impatiens )
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Insectes Sociaux
RESEARCH ARTICLE
On the relationship between aggression and reproduction in pairs of orphaned worker bumblebees (Bombus impatiens) E. D. Sibbald • C. M. S. Plowright
Received: 9 April 2012 / Revised: 18 August 2012 / Accepted: 10 September 2012 / Published online: 29 September 2012 International Union for the Study of Social Insects (IUSSI) 2012
Abstract This study characterized aggression and reproduction within pairs of orphaned bumblebee sisters (Bombus impatiens (Cresson, 1863)). Twenty-one pairs were filmed in the laboratory over 5–10 days. Frequencies of aggression and egg-laying were obtained for each bee, and the presence or absence of brood was manipulated. Aggression and egglaying were more likely to co-occur in pairs placed without brood compared to pairs placed with brood. A significant positive correlation was found between members of a pair in the rates of aggression. In addition, a strong positive correlation was found in their rates of egg-laying: bees that had more sons also tended to have more nephews. The results show that under conditions of unrestricted food availability, behavioural interactions are compatible with continued reproduction by both orphaned workers. Though aggression may limit reproduction, it seems either to be an ineffective means of obtaining a reproductive monopoly in some situations and/or to be a set of behaviours invested with other possible functions. Keywords Bombus impatiens Orphaning Reproduction Aggression Dominance Inclusive fitness
Electronic supplementary material The online version of this article (doi:10.1007/s00040-012-0261-7) contains supplementary material, which is available to authorized users. E. D. Sibbald C. M. S. Plowright (&) School of Psychology, University of Ottawa, Ottawa, ON K1N 6N5, Canada e-mail: [email protected] E. D. Sibbald e-mail: [email protected]
Introduction In bumblebees (Bombus spp. (Latreille, 1802)), workers retain their reproductive capabilities; although they do not mate, they can lay unfertilized eggs that result in male offspring (Sladen, 1989). Not all the workers lay eggs [by one estimate, 38 % of workers (Bombus terrestris (Linnaeus, 1758)) had laid eggs by the end of the colony cycle (Alaux et al., 2004b)], and those that do, carry out little work while the rest perform the regular activities of colony maintenance (Ratnieks et al., 2006). This leads to the question of what differentiates the reproductive from the non-reproductive workers. The common assumption is that a form of reproductive competition takes place (Johnstone, 2000). Specifically, an agonistic encounter determines the egglaying ‘winner’, while the loser must resort to caring for her sister’s offspring. In the slave-making ant (Harpagoxenus sublaevis (Nylander, 1849)), aggressive workers have increased ovarian development (Bourke, 1988). Similar associations are also observed in other eusocial insects such as the wasps, Polistes chinensis antennalis (Perkins, 1905) (Miyano, 1986), Parachartergus colobopterus (Licht, 1796) (
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