Larval competition does not affect the frequency of androchrome females but changes sex-ratio in Ischnura graellsii (Odonata: Coenagrionidae) 00

Abstract

The maintenance of colour polymorphisms in natural populations is often explained by contrasting selective forces acting on the life cycle stage that shows the polymorphism. Nevertheless, in animals with complex life cycles, selection during the larval stage, which usually is the longest development phase and might accumulate 99% of overall mortality, could be a determinant force if the genes that affect adult colour have pleiotropic effects on larval phenotype. Among odonates, female colour polymorphism is under selection during the adult stage, but very little is known about its effect during larval development. In this paper, we studied the coenagrionid damselfly Ischnura graellsii which shows three genetically determined female morphs. We explored the effects of the colour polymorphism and sex by undertaking a selection black-box experiment in microcosms, repeated over two years, to evaluate whether different densities and food stress may lead to variation in emerging adult morph frequencies and sex-ratios. We found that female morph frequency did not significantly differ between density treatments or years, and detected a significant effect of treatment on sex-ratio and body size, but not on developmental time. Furthermore, we found significant between-year variation in body size and developmental time. We conclude that the effect of colour phenotype on larval competitiveness seems limited and discuss the importance of experiment replication to increase confidence in the generality of results.

Keywords: Zygoptera, colour polymorphism, competition, damselfly, larvae, morph frequencies, replication of experiments

Issue section: Original Article