Copulation-associated colour change in Argia apicalis (Odonata: Coenagrionidae)

In Odonata, the gradual development of adult colouration during their post-eclosion teneral period is a well-know phenomenon, and these morphological colour changes occur slowly and irreversibly.  Physiological colour change, on the other hand, is always rapid and reversible, and has only been studied in only a few insect species.  A diverse set of theories have been put forth in an effort to explain the mechanism controlling the colour change, as well as the adaptive benefit that it offers.  While the change exhibited by most species is primarily temperature sensitive – changing to dark-phase colouration when below a certain temperature threshold, and then returning to their bright-phase when the temperature rises above it – this is not always the case.  Although not yet documented, it has been witnessed on several occasions that male Argia apicalis also change colour – from bright-phase to dark-phase – during copulation.  Given past research into the selective advantage of physiological colour change, the ability to change colour in direct response to copulation could offer multiple rewards.  The capacity to thermoregulate while in copula may well be beneficial, as would cryptic colouration in regards to predator avoidance.  Since colours are often so important in intraspecific communication, it could be to A. apicalis’ advantage to advertise their readiness to mate while in bright-phase, and then make themselves less conspicuous during copula by transforming into dark-phase. I am currently in the process of working to document the phenomena’s existence, and future work will be geared towards determining the mechanism that drives it.