Lifetime mating success in a marginal population of a damselfly, Coenagrion mercuriale

Abstract

In scrambling species, where males obtain matings by actively searching for females, the timing and location of mating may be more important to females than choice of males based on phenotype. Since their activity rates are constrained by climate, variation in lifetime reproductive success in marginal populations of scrambling insects may be governed primarily by stochastic processes, limiting the role of selection. Using multivariate analysis, we examined activity patterns and lifetime mating success (LMS) in a marginal British population of Coenagrion mercuriale, a rare, scrambling damselfly, versus that in a core population of a similarly sized scrambling congeneric. Time spent at the breeding site and mating efficiency were the most important factors explaining variation (<75% correct predictions) in LMS in both species, whereas body size, age, and day of entry to the mature population were unimportant. This suggests that LMS in these scrambling species is governed by sexual and natural selection as well as stochastic processes such as weather. However, in C. mercuriale, daily mating and activity rates were highly constrained by poor environmental conditions (and increased with sunlight and temperature). Breeding site visits were so curtailed that an equal distribution of LMS between the sexes was observed. Selection in marginal populations of C. mercuriale may operate upon traits that confer endurance ability in poor environmental conditions rather than body size, life span or age. Climatic variation across species' ranges will in turn generate geographical variation in mating behaviour, in the intensity of sexual selection and the type of traits selected.