Welcome to part two of my odonate trilogy! Last time I discussed the reasons why I think dragonflies are the best insects. However, I didn’t talk about the final reason I think dragonflies are amazing and that is the subject of today’s post: dragonflies are territorial!
Even if you aren’t a biologist, you probably know a bit about territoriality already. Ever see a dog lift his leg on a fence or a tree? That is a territorial behavior, a way for the dog to say, “This is MY space, so I’m going to mark it as mine!” In canines, males mark territories with urine and other odorous compounds so that they can chemically signal to outside dogs that the space they are marking is part of their territory (the space in which they hunt and find mates) and that outside males should stay away if they want to avoid a confrontation. They’re trying to convince other dogs that they are bigger and badder and that they can take on anyone that wants to challenge them for their space. Naturally, your dog peeing on a tree doesn’t have quite the same meaning as it might if it were a coyote or a wolf doing the peeing. After all, it’s hard to defend a territory on a leash! Still, the behavior hasn’t entirely disappeared from our domestic pets and so our male dogs continue to pee on trees. (And yes, I am resisting the urge to post a picture of my dog peeing on my fence!)
Male dragonflies are also territorial, but their system is very different from canines and is more behaviorally complex in many ways. Let’s go over the process!
A typical dragonfly habitat
First of all, males are territorial because females choose mates based on who provides the best real estate for her eggs. For a female dragonfly, this might be a nice mat of algae, open water, or a stand of cattails – different species will look for different things. A female dragonfly will go to an appropriate body of water (flowing or still, depending on the species), find the best place to lay her eggs, and mate with whatever male happens to be in the area. The females of some species require courting rituals, but others will just mate with the male in the area. The pair mates as described in my last post and the female will lay eggs in the area she has chosen. Then she’ll fly off, perhaps waiting a few more days to return to the water to lay some more eggs or simply moving to another spot.
Because females choose mates based on the quality of oviposition sites (the word oviposition means to lay eggs, so an oviposition site is the location where eggs are laid), males who remain in the best areas will be able to mate with more females than those who are in lesser quality areas. It’s even better if you’re THE ONLY male in that really great spot so you get all of the females. Hence, territoriality began! Male dragonflies will protect an area from other male dragonflies of their species so that they will have the best chance at mating with as many females as possible. The best male (generally considered the most “fit” male by evolutionary biologists) is able to protect the best spots from his competitors. The less fit males, the ones who are unable to chase the best males out of their areas, will take the less fabulous oviposition sites. The males who are not able to hold any spot will sometimes hang out around the body of water and wait for a space to open up or try to sneak matings while the residents are preoccupied. These comparatively unfit males will also sometimes leave the area entirely in search of another body of water.
A green darner (Anax junius) male patrolling his territory
So how does this territorial behavior work? Let’s envision a hypothetical pond where no dragonflies have ever set up territories. The first dragonfly arrives and takes the best oviposition site. Depending on the species he belongs to, he will find a good place to rest while he watches his area or he will fly around his area continuously in a behavior called patrolling. When another dragonfly comes along, unless there is another spot of nearly the same quality he can claim, he probably wants the same spot as the first male to arrive. In this case, the new male will challenge the resident male for the position. To do so, he will fly into the territory and the resident male will fly out to greet him. The two will engage in a ritualistic fight where they chase each other, flying around one another in circles very rapidly and zipping across the pond, to demonstrate their strength (effectively their fitness) to one another. Minimal physical contact occurs between the combatants (this is important when you have rather fragile wings that you depend on for everything you do!), but the male who would lose if they actually came to blows will likely give up his claim on the spot and take the next best spot. More males arrive and fight for the spots that they want, shifting the territories between individuals. Eventually, a sort of equilibrium is reached where the best males have the best spots, the lesser males have the lesser spots, and the weakest males have no spots.
Protecting a good territory is hard work and even the best dragonflies can’t protect them forever. A male protecting the most popular oviposition site will be constantly challenged by neighbors and the males who are unable to claim territories, not to mention he’s getting more matings than any other dragonfly at the pond! Male dragonflies also expend a lot of energy guarding their mates while they lay their eggs. An unprotected female is likely to be grabbed by another male and taken to another location at the pond to mate again before she finishes laying the eggs the resident male just fertilized, and males put a lot of effort into guarding their mates. So, territories often shift during the day as more energetic males overthrow tired resident males. Younger males can usurp territories from older males as well. And there are always those males who weren’t quite strong enough to claim a territory waiting for resident dragonflies to weaken to the point that they can finally overcome them and take over their positions.
Green darner (Anax junius) males in combat
Competition for territories can be fierce. There are usually far fewer territories at a body of water than there are male dragonflies who want them, so they are constantly trying to claim better territories and mate with as many females as they can. It’s effectively a war zone! The competition doesn’t ease once all of the territories are taken either as more dragonflies may arrive at the pond and many of the less fit males stay nearby in hopes of eventually gaining a territory.
In general, males who hold territories mate many more times than males that do not have territories, but even the homeless males will secure some mates. While a male is chasing another male from his territory, a weaker male might be able to slip in and grab a quick mating. Males who are guarding females are less likely to chase intruders from their territories until the female is finished laying her eggs, so weaker males can sometimes take advantage of their lapse in attention to sneak in a mating. It is also typical for males with lower quality territories to mate more often than males without territories. You might thinks that males holding lower quality territories would never get mates and waste their energy protecting their sites because females choose mates based on who holds the best oviposition site. However, females are in such short supply and such high demand that they are sometimes mobbed when they arrive at the best spots because so many males are competing for the same space. A female who is harassed enough or has her egg laying interrupted enough times will seek a mate in a quieter area where she may lay her eggs in peace.
So, male dragonflies form territories so that they can mate with as many females as they can. The more females they mate with, the more offspring they will produce and the more their genes are passed on. Pretty simple really! And it’s one major reason many other animal species set up territories too.
Next time, I’ll finish up my dragonfly trilogy by cheating a bit and using the British definition of dragonfly (they use dragonfly for both dragonflies and damselflies) so I can talk about a recent paper about territoriality in a damselfly species. Damselflies are much less likely to protect territories than dragonflies, but the system works the same way. I hope you’ll stay tuned!
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