Alternative mating tactics in male white-faced dragonflies (Leucorrhinia intacta): plasticity of tactical options and consequences for reproductive success

Abstract

Alternative tactics used by males to obtain mates usually are associated with genetic and/or phenotypic differences between the behavioral morphs. This system of white-faced dragonfly (Leucorrhinia intacta) alternatives is characterized by plasticity of tactical options for individual males. Males may act either as territorials, and defend small perch-centered territories on the study pond, or they act as transients, spending most of their time in vegetation surrounding the pond and sallying out at intervals in search of mates. The two tactics remain in constant proportions over a broad range of densities, so transients do not result only from a ‘filling in’ of suitable territorial sites. Males adopt tactics independently from day to day, with no significant influences of phenotypic variation, priority of arrival at the breeding site, or prior success in a role. We interpret this system as based on conditional, frequency-dependent choice of alternatives by a population of males not differing significantly in their abilities to employ one tactic or the other, but we cannot exclude entirely the possibility of mixed strategies. Average daily mating success is equal for territorial and transient males, supporting predictions of mixed and conditional ESS hypotheses. Males of each tactic obtain matings daily in proportion to their representation in the population for most data samples. Deviations from the expected mating success provide no information of use in selecting one or the other tactic on subsequent days. We suggest this system of alternatives represents a conditional mating strategy, in which males adopt tactics based on the availability of perches relative to oviposition substrate and on interactions within and between tactics that are influenced by the relative frequencies of territorial and transient males.