Male biased sex ratio reduces the fecundity of one of three female morphs in a polymorphic damselfly

Females of the damselfly Ischnura graellsii display 3 color morphs, a male-like androchrome morph and 2 other morphs, infuscans and aurantiaca, which are not male-like. Previous research has suggested that male harassment has a negative effect on female fitness in many different insect species. Studying how male harassment affects fitness of the different female color morphs is key to a better understanding of how these morphs are maintained in natural populations. This study evaluated the response of female morphs of I. graellsii to contrasting sex ratios under controlled laboratory conditions. In our experiments, male abundance, through increased harassment, affected differentially the fecundity of females of the 3 color morphs. A male biased (3:1) sex ratio drastically decreased the average fecundity of infuscans females but had no effect on androchrome and aurantiaca females. Taking into account our results and previous studies that indicate that males prefer infuscans females, we p...