Dragonflies are wonderful subjects of biological investigation, because they are large, fulfilling to catch, photogenic, don't bite, and do some very interesting things. One day, while lying in a patch of poison ivy (which I only identified later), I observed a Darwinian puzzle. Male dragonflies defend territories which are used exclusively for the purposes of mating. In general, females fly in, males grab them, they mate, and the females lay eggs in the territory. Given that fights are energetically costly, and potentially injurious, I expected them to only occur between males of the same species. This was not the case. This minor observation spawned my doctoral dissertation research into the behavior of Leucorrhinia dragonflies. L. frigida and L. intacta are equally likely to exclude conspecifics (same species) or heterospecifics (other species), while L. proxima is more likely to defend against intrustions by conspecifics. My research provided evidence that species recognition is costly to a territorial male, because while the male determines the species identity of an intruder, he may suffer a tactical cost that reduces his fighting ability.
Along similar lines, Male Leucorrhinia dragonflies attempt to mate with conspecific and heterospecific females. Heterospecific matings attempts are usually unsuccessful, as the pair disengages after assuming the mating position. Males of all three species show no evidence of species discrimination while they are guarding their egg-laying females. This lack of discrimination is very costly, because about 30% of the times in which males lost their females to amorous intruders, they were off chasing heterospecific males, who presumably posed no reproductive threat.
The last thread of my dissertation research was an investigation into variation in mate guarding in Sympetrum obtrusum. Males may use noncontact guarding or tandem guarding to protect their females from intruding males while they are laying eggs. Noncontact guarding is less effective, but energetically less costly. I discovered that cold temperature and high wind speeds (i.e. a high wind chill factor) lead to low flight muscle temperatures, so the male physiologically can't support the female while she lays her eggs. He may pay the ultimate Darwinian price for his lack of flight muscle performance.
Above you can see a Sympetrum male relaxing in the sun. One final advantage of dragonfly research is they work banker's hours, and are only active on sunny days. I'd be delighted to direct some field research on the abundant diversity of dragonflies we have in southwest Virginia.
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