Population biology and phenology of the colour polymorphic damselfly Ischnura elegans at its southern range limit in Cyprus

1. Geographically widespread species provide excellent opportunities to investigate how phenotypes change across large-scale environmental gradients. Temperature is a fundamental environmental variable and an important determinant of insect fitness. However, field research is often geographically restricted, and typically concentrated in northern latitudes. Basic population biology and phenotypic clines in relation to temperature therefore remain poorly known across the entire geographic range, even in otherwise well-studied taxa. 2. We surveyed populations of the trimorphic damselfly Ischnura elegans in Cyprus, which is the southern range limit in Europe of this widespread insect species. Females of I. elegans occur in three discrete and heritable colour morphs, which vary in suites of phenotypic traits. One of these female morphs is a male-mimic that avoids excessive male-mating harassment by its male-like appearance, and which is more cold-tolerant than the two other morphs. 3. In contrast to the situation in northern Europe, these male-mimicking females are the minority morph in Cyprus, representing only about 5% of all females. Male mimics also have lower mating rates than alternative female morphs. 4. Individuals in Cyprus are relatively small in comparison to the reported European range for body size, consistent with Bergman's rule. 5. Finally, populations of I. elegans on the island have the longest flight period known in Europe, and there is only partial evidence for seasonality in flight activity. 6. These results underscore the benefits of considering the entire range of environmental conditions encountered by insect species when conducting evolutionary ecology research.