Fluctuating environments cause context-dependent mate preferences in early population divergence

Attached you will find the R scripts and the accompanying data frames used to generate the results for this manuscript. Please refer to the attached README for instructions on how to use the scripts and data. Fluctuating environments cause context-dependent mate preferences in early population divergence Abstract Understanding the factors shaping premating isolation in the early stages of population divergence is a major challenge in ecology and evolution. Context-dependent mate preferences that change with environmental conditions could either promote or counteract the development of premating isolation. Here, we investigated how environmental conditions and male origin affected female mate preferences in the colour polymorphic Common Bluetail Damselfly (Ischnura elegans). Closely located populations of this species differ in female colour morph frequencies, densities and species community composition, but there is extensive dispersal and gene flow between populations. We quantified female mate preferences for resident and immigrant males across years that differed in environmental harshness, revealed by interannual variation in female fecundity. Females showed highly context-dependent mate preferences: in a benign year, females preferred immigrant males, whereas in an extremely harsh year this pattern was reversed, and females instead preferred resident males. Furthermore, in the harsh year, field mating rates were low, and females were more prone to copulate in our experimental mate choice trials, indicating mate limitation and relaxed sexual conflict under harsh conditions. Female preferences for immigrant males in the benign year were unlikely due to inbreeding avoidance, as we found only weak population genomic structure and low fixation indices (FIS). Instead, female preferences for immigrant males when field mating rates are high is consistent with “chase away sexual selection”, whereby females develop resistance against mating harassment from local males. Unexpectedly, we found no differences in mate preferences between female colour morphs. Our study reveals that female mate preferences are highly context-dependent and shaped by environmental fluctuations, with implications for the development and stability of premating isolation.