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

Females of the damselfly <i>Ischnura graellsii</i> display three colour morphs, a male-like androchrome morph and two other morphs, <i>infuscans</i> and <i>aurantiaca</i>, 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 colour 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>I. graellsii</i> to contrasting sex ratios under controlled laboratory conditions. In our experiments, male abundance, through increased harassment, affected differentially the fecundity of females of the three colour morphs. A male-biased (3:1) sex ratio drastically decreased the average fecundity of <i>infuscans</i> females but had no effect on androchrome and <i>aurantiaca</i> females. Taking into account our results and previous studies that indicate that males prefer <i>infuscans</i> females, we propose a mechanism for the maintenance of this polymorphism. In this scenario, within-generation fluctuations in male abundance produce two regimes: One in which male abundance disfavours <i>infuscans</i> females by decreasing their fecundity and other in which a low male abundance results in androchromes that do not mate because of their low appeal to males. By studying a simple population genetics model, we found that the mechanism that we propose may contribute to maintain a stable female-limited polymorphism under a wide range of parameter combinations.