Phenotypic variation in male Calopteryx splendens damselflies: The role of wing pigmentation and body size in thermoregulation

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.