For an ectothermic insect, its color and size are important determinants of body temperature: dark colors absorb heat more efficiently, while larger bodies require more heat to reach a certain temperature. These dark colors are expressed using melanin, which has been intimately linked with an insect’s thermoregulatory capabilities. Melanin is also linked with immune defense and is often used as a secondary sexual character in insects. There is a potential trade-off situation between thermoregulatory capabilities, immune defence and secondary sexual characters, all of which use melanin. Some Calopteryx damselflies, such as Calopteryx splendens, have melanin-based wing pigmentation that is sexually selected and drives intra- and interspecific territorial aggressions. Our goal was to experimentally study how the wing pigmentation and body size of C. splendens males affect their thermoregulation and especially their ability to become active after being cooled down. Our results are in line with our hypotheses showing that (i) individuals with larger wing spots had significantly faster activation times than those with smaller wing spots, and (ii) individuals with larger body size had significantly slower activation times than those with smaller body size. Both variables showed an interaction and thus are important in damselfly warm up and activation. We discuss the role wing pigmentation and thermoregulation can have on the behavioral patterns observed in Calopteryx species.

The dataset was collected by measuring temperatures and activation times of damselfies (Calopteryx splendens) in laboratory conditions. The wing length and wing spot length were also measured. Relative wing spot size was calculated by using following formula: 100* wing spot length / wing length.