Female-limited colour polymorphism is widespread in Odonata, particularly in the Coenagrionidae, where it is determined by simple Mendelian inheritance. In contrast, female-limited colour polymorphism in Calopterygidae is restricted to some populations of the Palaearctic Calopteryx splendens complex, whose males have blue-spotted wings and females occur either as gynochromes with transparent wings or as androchromes with dark brown-spotted wings. A behavioural study in two river basins in southern Italy suggested that reduced harassment by males of the syntopic Calopteryx haemorrhoidalis might favour androchrome females, which could otherwise suffer increased predation due to their less cryptic coloration. However, the role of interspecific harassment in maintaining this polymorphism has not been further tested. Here, the results of three field surveys conducted in southern Italy in 2011, 2020, and 2021 are reported, expanding the known range of polymorphic C. splendens populations to 22 sites across seven river basins. Two distinct androchrome morphotypes were identified, differing in the extent of wing pigmentation: one widespread in the Basilicata and Campania regions and another restricted to the Crati river basin in the Calabria region. The proportion of androchrome females was associated with the river basin and the density and proportion of conspecific males, not with the density or proportion of C. haemorrhoidalis males. Contrary to earlier behavioural evidence, these results suggest that female-limited polymorphism is not maintained by interspecific harassment but by intraspecific mechanisms such as male mimicry or frequency-dependent selection.
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