Assortative mating, where individuals mate non-randomly with respect to phenotype or genotype, can have profound evolutionary consequences. However, little is known about the underlying mechanisms and consequences of assortative mating, especially in polymorphic species. The common bluetail damselfly (Ischnura elegans) is a polymorphic insect with three heritable female colour morphs, including a male mimic. This polymorphic system is characterized by strong and spatially varying sexual selection. Here, I investigated the mechanisms of assortative mating within and among populations of this species where I quantified the direction and strength of assortative mating on body size and its effect on fitness within populations, including morph specific effects. I used a 22-year data set of mating pairs of I. elegans, with known body size and female fecundity of the three colour morphs from multiple field populations in southern Sweden. I have conducted a mate-choice experiments and quantified the direction and strength of assortative mating with respect to both body size and in relation to immigrant status (resident vs. foreign males). This colour polymorphism is sex-limited in expression and only visible in females. Since morph determination is due to a single autosomal locus, males also carry the colour alleles even if they do not phenotypically express the polymorphism. I am currently genotyping males and females with respect to the morph locus. I will use this information to investigate if the morph locus affects assortative mating in both sexes.
The effect of assortative mating on colour morphs, body size and population of origin in a polymorphic insect