Pheromonally mediated mate attraction by males of the burying beetle Nicrophorus orbicollis: Alternative calling tactics conditional on both intrinsic and extrinsic factors

Male burying beetles attract females using a pheromonal signal and can provide parental care and a food resource, vertebrate carrion, for their developing offspring. But males attempt to attract females even when they have no carrion. We examined the factors that influence male behavior directed toward finding or attracting mates in both field-caught and laboratory-reared Nicrophorus orbicollis, a North American burying beetle. We investigated whether male behavior differed based on both intrinsic (size) and extrinsic (resources held) differences among males. Further, we examined repeatability of individual behaviors and the effect of holding or lacking resources on these repeatabilities. Field-caught and laboratory-reared individuals differed in overall activity but not in their behavioral repertoire, making studies of laboratory-reared males relevant. The behavior of individual males was very consistent within a condition, but plastic between resource conditions. The frequency of calling (adopting a posture that indicates pheromone release to attract females) depended on male size when males did not hold resources, but this relationship disappeared when males held resources. Without carrion, smaller males called more frequently than did larger males. When holding carrion, smaller males reduced their calling, whereas larger males significantly increased the frequency with which they attempted to attract females and reduced the amount of time they spent searching. Thus, calling behavior of males was conditional on not only intrinsic and extrinsic factors, but also an interaction between them. We suggest that the changes in calling represent alternative tactics based on the costs and benefits of attracting both potential mates and competitors, which differ for males of different sizes.