Female colour polymorphism in damselflies: failure to reject the null hypothesis

Abstract

Abstract. The adaptive significance of colour polymorphisms in adult females within the Odonata remains controversial. Proposed benefits for male-like andromorphs include increased reproductive isolation and/or decreased harassment from conspecific or heterospecific males. Proposed costs balancing such benefits are increased predation on andromorphs, and/or failure of andromorphs to mate at low male densities. Nevertheless, data from past studies are insufficient to reject convincingly the null hypothesis that colour polymorphisms are neutral with respect to natural or sexual selection. Long-term data on two species of Enallagma damselflies are presented that are consistent with the null hypothesis. Male responses to tethered females suggested that males more readily recognize the most abundant morph as 'female'. Nevertheless, the two colour morphs did not differ in the time of day that they were seen in tandem, daily or lifetime mating frequency, life span, oviposition duration, inter-clutch interval, or maturation rate. These results indicated that male discrimination between morphs was predictive of neither costs nor benefits of the polymorphism in terms of female reproductive success.