Sex ratio in a population of Lestes viridis: spatial and temporal variability at emergence (Odonata: Lestidae)


In a large population of Lestes viridis inhabiting a complex, extended system of channels in the floodplain of the Upper Rhine River near Weisweil (Baden-Württemberg, Germany) detailed samples of exuviae were collected from several subpopulations. For each sample the sex ratio was determined. For statistical reasons only samples with at least 700 exuviae were considered. These samples sometimes differed highly significant in the sex ratio at emergence. The sex ratio was site-specific, but differed significantly for different subpopulations with variation in water temperature. Thus, damselfly larvae showed sex-dependent habitat preferences. The frequency of males ranged from 49.4% to 57.5%. Statistically significant small-scale differences in sex ratio, which have not previously been described, could not be attributed to different preferences of the sexes with respect to larval habitat and emergence site. No coherent explanation for this phenomenon could be advanced. Females on average emerged earlier than males; in one of the samples the median emergence date differed by four days.

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