Environmental heterogeneity and alternative mating tactics in the damselfly Protoneura amatoria

Conditional male mating strategies have been studied extensively in relation to male attributes, such as size and resource-holding potential, but few studies have considered the effects of environmental heterogeneity on the use of alternative mating tactics. In some systems, environmental heterogeneity may be the key to understanding the evolution and maintenance of such polyphenisms. I examined the influence of the physical environment on the use of alternative tactics by the damselfly Protoneura amatoria. Male P. amatoria reversibly use 2 tactics to gain matings: 1) sit and wait in the canopy for passing females or 2) hover over the water and attempt to grab females that are ovipositing in floating debris. Observations in 3 streams indicated that the use of the hovering tactic was greater under high-light than low-light conditions and at higher densities of ovipositing females. The density of ovipositing females was correlated with both the light conditions and the availability of oviposition substrate, indicating that physical factors exert indirect as well as direct influences on tactic use. Experimental manipulations showed that both males and females responded directly to light conditions and suggested that males responded directly to the density of ovipositing females. These results can be explained largely in terms of the cues and constraints inherent in different light environments. Thus, the conditional mating strategy of P. amatoria appears to have evolved in response to, and been maintained by, fine-scale variation in the physical environment. These findings are discussed in relation to flight dynamics and predation risk. Copyright 2007, Oxford University Press.