Christopher W. Harbison
Department of Biology, Carleton College, Northfield, MN, USA, 55057
Abstract. According to current theory, mate guarding occurs when the fitness gained by guarding the mated female from extra-pair copulations is greater than the fitness gained by finding and mating with other females. It has been proposed that the millipede Nyssodesmus python displays mate-guarding behavior (Heisler 1983). After copulation, a male will ride on top of the female for up to 5 days, preventing other males from copulating with the female. This study examines the mate-guarding hypothesis for N. python by separating mated pairs, placing an unmated male in close proximity, and observing the interactions between the males and the female. While results were variable, mated males were observed remounting the female, and an unmated male was observed mounting and copulating with a female. These results suggest that mate-guarding is the most probable cause for the observed riding behavior.