Alternative mating tactics in male white-faced dragonflies: experimental evidence for a behavioural assessment ESS

Locations of artificial perches were manipulated relative to oviposition substrate to test whether the maintenance of discrete, daily alternative mating tactics, either territorial defence or wandering to encounter reproductively active females, among a population of male white-faced dragonflies, Leucorrhinia intacta, was better described by a mixed ESS (probability of tactic use fixed in ecological time) or behavioural assessment ESS (probability of tactic use varies with environmental conditions) model. Females responded to the manipulations by ovipositing significantly more frequently in areas with good oviposition substrate. Territorial males settled where artificial perches occurred, but preferred perches in areas with good oviposition substrate. Sequential daily manipulation of perch position produced significant effects on tactic frequency. A significantly lower proportion of the male population exhibited territoriality when perches were not in areas with good oviposition substrate than when perches were either all in areas with good substrate or equally distributed between areas with and without good substrate. Tactic frequencies did not differ significantly between the latter two experimental configurations. Average reproductive success, measured as eggs laid by females mated to males using each tactic, generally was not statistically different within experimental treatments. The data support a changing probability of using a tactic (behavioural assessment ESS) and not a fixed probability (mixed ESS). It is hypothesized that natural variation in availability of perches and substrate, even within the short adult life of these dragonflies, selects for flexibility of tactic choice by individual males. Mechanisms of assessment and the factors producing negative frequency dependence of payoffs to one or both tactics are unknown at present.