Environmental heterogeneity and the evolution of alternative mating tactics in the damselfly, Protoneura amatoria

The evolution and maintenance of conditional male mating strategies have been studied extensively in relation to male attributes, such as size and resource holding potential. In the most well studied species, each alternative tactic is associated with a discrete morph, the larger of which is typically territorial, and the smaller of which uses a sneaking tactic. In these species, tactics appear to be maintained by frequency dependent or density dependent selection. Rarely have species that exhibit alternative tactics that are not associated with distinct phenotypes been studied in depth, and beyond variation in frequency or density, few studies have considered the effects of environmental heterogeneity on the use of alternative mating tactics. The goal of this study was to examine the roles of environmental heterogeneity and male morphology in a species with continuous morphological variation. Using the damselfly Protoneura amatoria I investigated: (1) how environmental heterogeneity influences tactic use and fitness, (2) how morphology influences tactic use and fitness, and (3) whether the environment in which a male finds himself influences the relationship between morphology and tactic use or fitness.; Males of P. amatoria reversibly use two 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 (guarded or solitary) that are ovipositing in floating debris. Both tactics are territorial.; Observations of damselflies on three streams showed that the frequency of the hovering tactic increased as light availability and densities of ovipositing females increased. Experiments indicated that these two variables directly influenced tactic use. To investigate the influence of these factors on the fitness of the two tactics, marked populations were studied. When males used the hovering tactic they had greater mating success with high light availability and high densities of ovipositing females. When males used the perching tactic their mating success was not strongly influenced by these factors. Using these same marked populations, I found that the relationship between morphology and tactic use was strongly frequency dependent. The relationship between morphology and mating success was also found to be frequency dependent. These results can be explained largely in terms of trade-offs between the energetic demands of flight and competitive ability, which vary across situations.