Susanne P.A. Den Boer1, Boris C. Baer2, and Jacobus J. Boomsma1. (1) Department of Population Biology, Institute of Biology, University of Copenhagen, Universitetsparken 15, DK-2100, Copenhagen, Denmark, (2) School of Animal Biology, The University of Western Australia, Nedlands, WA 6009, Perth, Australia
Social insect queens mate early in life, during a single or very few dispersal flights and never remate once they have started to lay eggs. During these flights queens collect and store sperm in their spermatheca and will use this to fertilize eggs throughout their life. In some species such as leafcutter ants, these queens can have a lifespan of several decades and can build colonies with millions of workers. Sperm is therefore thought to be a limiting factor for reproduction and as a consequence there should be severe selection pressure on queens to use only a minimal amount of sperm to fertilize an egg. We developed a new technique that allows direct measurements of the number of sperm present on freshly laid eggs. For the leafcutter ant Atta colombica, we found that queens use 2-4 sperm to fertilize an egg. These numbers are similar to earlier, but indirect estimations for the fire ant Solenopsis invicta and the honeybee Apis mellifera. Furthermore, our technique will allow us to address a number of novel questions, for example whether the economy of sperm use varies with queen age or the total amount of sperm stored.
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