The evolution of continuous variation in ejaculate expenditure strategy
09/3/10, 15:30 at Room 3631 (6th floor of building 3 of the Faculty of Sciences)
Sperm competition theory has focussed on the evolution of ejaculate expenditure strategies across different species, populations, or discrete mating roles characterised by different levels of sperm competition. Few studies have considered the extent to which male ejaculate expenditure is influenced by continuous change in male phenotype within a population. Here, we model how optimal ejaculate expenditure responds to two sources of continuous variation: the quantity of resources allocated by a male to mating within a breeding season, and the resource cost of obtaining a mate. We find that when males vary in the amount of resources available for reproduction, all males are selected to use the same ejaculate expenditure strategy. However, when males vary in the cost of obtaining a mate, males with a lower cost will be selected to invest fewer sperm per mating than males whose cost is higher. These results provide a novel insight into the evolution of male ejaculate expenditure strategies, showing that individual constraints on the ability to secure matings can lead to variation in ejaculate expenditure even when the risk of sperm competition is the same for all males.
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