Scale

Today’s Photography 101 topic is “scale” and I decided to take a trip to the pond after work today to take this shot:

 
The front half of what you can see in the photo represents about 50% of the territory of the strongest green darner dragonfly at this pond. It will fly back and forth across this area hundreds of times each day that it manages to keep control of the territory. It’s quite a large area for a 3 inch long insect to patrol and maintain control over. In fact, there’s a dragonfly in the photo to give you a sense of how big the space is relative to the insect. Can you find it? Trust me, it’s there, right there:

 
I’m always impressed by how huge the territory for some of the large dragonflies are. Insects never cease to amaze me.

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Unless otherwise stated, all text, images, and video are copyright © C. L. Goforth.

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One Long Sentence About Dragonflies

Pachydiplax longipennis maleThis week’s Monday post is going to be comparatively short on the educational value, but I figure that’s okay now and again.  I participated in an academic writing workshop with 49 other grad students earlier this summer and it was, with one exception, a great experience.  I learned a lot and enjoyed the activities.  Plus, I made some great progress on my dissertation.  Woohoo!  Seeing as that was the reason I had applied for the workshop in the first place, mission accomplished!

One of the many activities we did as a group was an exercise in varying sentence length and controlling long sentences.  Two goals of the session were to show us how easy it is to write epic sentences, ones that go on and on forever, and how unpleasant they are for readers.  The idea was that once we realized that we are all capable of writing insanely long sentences, we would look out for them as we write in the future.  So, we were given ten minutes and asked to write the longest sentence we could with pen and paper on a topic of our choice.  I wrote about dragonflies because I’m just that sort of person (but you all know that already, right?) and it’s a topic I know a lot about.  Thus, I present my 377 word long sentence about dragonfly territorial behavior!

Libellula saturata femaleThe dragonfly, with its clear and membranous, faintly gossamer wings, darts over the still pond, the water reflecting the morning light and warming the air, releasing small puffs of water vapor into a thick cloud that lies over the calm water, a haze through which the dragonfly flies as he seeks his prey, zigging and zagging over the water and darting to and fro, following the tiny trails through the mist left behind by mosquitoes and other small flies, the flies buzzing obliviously through the air as they fly and go about their morning’s business of searching for food and shelter and sex so they can pass their genes on as proud parents of the next generation of little flies, worm-like beings swimming in the water alongside the children of their hunter, the dragonfly, he searching for food and mates above the water, protecting his little patch of clear water and green water weeds from usurpers, those who wish him harm and covet his territory, for it is good, and the mates it will bring, all the while hoping that a drab female will choose his territory (thereby choosing him as the virile and potent father of her young), and allow their violent embrace, the male grabbing his new beloved behind the head and dragging her about his territory, as if showing it off, before they complete the copulative act, he curling his body around so that his mate lies under him, and she stretching her body up for their most intimate embrace, both flying continuously as they hurry through their lustful encounter over the water before breaking apart so the female can lay her precious eggs among the water weeds, spilling her offspring into the water, her latest love conquest looking on protectively as she brings forth his progeny, progeny that will rest in the water before hatching into tiny, fierce predators that strut about the pond, knowing that they are bada** carnivores that hardly anything will touch, growing ever bigger and stronger until they crawl out of the water, break free of their nymphal skin, and emerge with fully formed, clear and membranous, faintly gossamer wings, ready to take their father’s place darting over the still pond, flying through the gentle mist above the water.

Sympetrum corruptum maleMy giant IS painful to read, don’t you think?  I tried to be as lyrical as possible and change up the transitions, but yikes!  And my sentence was only the second longest in the group too, about half the length of the longest!  The exercise really worked for me though because I now comb my papers looking for long sentences as I never did before.  I was also rather proud of myself for writing something that actually had some scientific merit AND circled back around so that the beginning and end were similar enough to illustrate the whole circle of life thing.  Plus, although it might be painful to read (and there’s no denying that), my epic sentence is pretty accurate for dragonflies that lay their eggs in fishless ponds.  So long as you ignore the anthropomorphism, that is.  I so rarely get to write things that are simply fun these days that I felt like I could get away with taking a few liberties.  :)

Perithemis intensa maleNext week I’ll have a more educational Monday post for you all.  There’s a sneak preview in this week’s Well-Nigh Wordless Wednesday too, so come on back on Wednesday!

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Unless otherwise stated, all text, images, and video are copyright © TheDragonflyWoman.com

Friday 5: Dragonflies Getting Busy

It is still cold in many parts of the US.  In fact, it even snowed in Tucson last weekend!  Having moved to Arizona from somewhere much colder, I know that winters can be dreary and sometimes it seems like the spring will never come.  So, let’s think about the good things to come in the spring and summer instead!  Today’s Friday 5 is all about something that’s coming soon to an area near you: dragonflies getting busy and making babies!

Step 1: The male finds and defends a territory.

defending territory

A male blue dasher (Pachydiplax longipennis) defends his territory from a perch.

Like many animals, male dragonflies attract females by showing off.   To have any chance at success in convincing a female to mate with him, a male dragonfly has to show how amazing he is by finding a good place for egg laying, setting up a perimeter around that area, and defending the space within that perimeter from other males.  This is hard work, but the males who defend the best territories tend to get the most girls, so it’s worth the effort.  Some dragonflies fly within their territories nearly constantly (these are “fliers”).  Others find perches within their territories (the “perchers”) and only fly when their territory is threatened by another male, or when they progress to Step 2.  (For more info on dragonfly territoriality, check out part II of my dragonfly trilogy for a whole post on the topic!)

STEP 2. The female flies into the area.

And all hell breaks loose! Dragonfly males may spend hours each day flying around in their territories, and it’s all in preparation for this moment.  It must be terribly exciting. When a female flies into his territory, the male will fly out toward her and try to grab her. If he is successful, he moves to Step 3.

Step 3: The male grabs the female.

male grasping female

A pair of desert firetails (Telebasis salva) shortly after the male has grabbed the female.

Success!  As you can see in the photo of the damselflies above, the male grabs the female behind the head.  Males need to get a firm grip because other males might try to steal the female from him and this is probably the best place to hold on.  This means that the male is grabbing the female with the section of his body where his sperm are produced, so he has to transfer sperm from the genitalia at the back end to a secondary set of genitalia up near the thorax before he grabs a female.  (Scroll down to the lower part of my post on why dragonflies are the best insects for more info on this and a photo of the two sets of genitalia.)  Females can refuse to mate with a male, even after he’s grabbed her.  If she’s unwilling, the male will eventually let her go her own merry way.  If she is willing to mate, they progress to step 4.

Step 4: The pair assumes the “wheel position” and mates

mating dragonflies

Dragonflies mating (Pachydiplax longipennis). The male is the blue dragonfly on top and the female is the brown-black dragonfly on the bottom.

To transfer sperm to the female, the male has to bring the genitalia at back end of the female into contact with his secondary genitalia near his thorax, all while maintaining his grip on her head.  He curls his abdomen under so that the female is held mostly parallel to his body.  She then curls her abdomen up toward his secondary genitalia.  In the process, they form the wheel position, this awkward looking position that looks like a circle drawn by a toddler.  Some dragonflies, such as the dragonflies in the photo, continue to fly in the wheel position and others land while in the wheel position.

Males are super competitive with one another when it comes to females, even at this stage.  If he is to be the biggest, baddest male at the pond (or stream), he needs to father the most children.  If a female has mated with another male before him, there’s a chance that the other male’s sperm is still stored in her sperm storage organ and might fertilize some of his gal’s eggs, even after he’s mated with her himself.  No problem!  Many male dragonflies have genitalia designed to scoop sperm out of females before he deposits his own.  Others do some really amazing things.  My advisor shows a video in his insect behavior lecture that shows a dragonfly in Germany that grabs the female and immediately whips her whole body around in a somersault, flinging the sperm from her body in the process!  Basically, males are selfish.  They want their offspring to be the only offspring in their territories and removing sperm deposited by other males from their mates before transferring their own sperm into the female helps ensure that this is realistic.

So the dragonflies get it on for a while.  Then they move on to Step 5.

5.  The female lays her eggs.

Anax laying eggs

A pair of common green darners (Anax junius) laying eggs. The males guards his female from usurpers by maintaining his hold on his mate.

Now that the male has successfully held a territory, encountered a female, and encouraged her to mate with him, there’s only one thing left to do: lay eggs!  However, there are a lot of males around the pond (or stream) and very few females, so other males may try to grab the female and mate with her before she finishes laying her eggs.  If that happens, they’ll remove the freshly deposited sperm and replace it with their own.  So a male who just mated with a female often guards her while she lays her eggs.  Guarding takes many forms.  Some males release their hold on the female and fly above them.  Others let the female go, return to their perches, and fly out to fight any potential usurpers.  Many species keep their hold on the female until she has finished laying her eggs, as in the green darners in the photo.

Egg laying habits vary from species to species too.  Some species fly over the water and dip their abdomens into the water several times, releasing eggs each time.  Some stay in one place, holding onto a rock or piece of vegetation, and lay all of their eggs in one spot.  Still others crawl all the way underwater to lay their eggs!  Many species just spray their eggs into the water and let them fall where they may, but some stick their eggs to rocks or vegetation or embed them into emergent plants or algae.  There is a lot of variation in egg laying and mate guarding behaviors, but they all accomplish the same thing: ensuring that the eggs a female lays in a territory are mostly those that have been fertilized by the male holding the territory.

When it warms up and the dragonflies come back out, I encourage everyone to find a pond or stream nearby and settle down to watch a little dragonfly porn.  Dragonfly mating habits are fascinating to watch!  You won’t be disappointed.

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Unless otherwise stated, all text, images, and video are copyright © 2011 DragonflyWoman.wordpress.com

From the Literature: Jocks and nerds in the damselfly world (The Dragonfly Trilogy, Part Three)

Welcome to the third and final segment of the Dragonfly Trilogy – and another installment of From the Literature!  If you don’t know anything about dragonfly territoriality, I recommend reading part two of my trilogy for more information on how dragonflies and damselflies set up and defend territories.  You’ll get more out of this post if you know something about territoriality before diving in.

Last time, I discussed how odonates benefit from being territorial, why they set up territories and defend them from other males.  Like many things in biology, it boils down to sex: males that defend high quality territories generally mate with more females than males with low quality territories.  Likewise, males that defend territories generally mate with more females than males that do not defend territories.  It is usually better to be a male with a territory than a male with no territory, but there are often many more males than there are available territories and some males are inevitably left out.  Presumably the stronger, better males (the most fit males) end up successfully claiming and holding territories while the weaker, wimpier males are left without territories and become wanderers.

Calopteryx virgo male

Calopteryx virgo male. Photo from Wikipedia, by Michael Apel.

This is the situation that a group of researchers  in Finland recently investigated.  They chose to study the damselfly Calopteryx virgo, a European damselfly also known as the beautiful demoiselle.  This gorgeous creature is pictured at left and is one of the damselflies known to be territorial.

The researchers asked a simple question: are C. virgo males that defend territories larger than males that do not defend territories?  They wanted to know if the damselflies that were able to protect a territory from other males were somehow better suited to being territorial than the damselflies doomed to be wanderers and unable to gain their own territory.  They also wanted to know if this changed over time, whether the non-territorial males eventually became territorial.

To answer these questions, the researchers captured mature C. virgo males arriving at their study stream in Finland, then marked them (so they could tell them apart), measured their right hindwings, weighed them, and released them back into the study area.  They observed the damselflies on two different days ten days apart and determined whether the males were territorial (they stayed within a small, 2 meter area for at least three hours) or non-territorial (they did not remain within a 2 meter area).  Males were considered wanderers if they moved more than 100 meters during the observational periods.

The team discovered that there was a significant difference in size between territorial and non-territorial males.  Territorial males had longer wings and were heavier than wandering males, so the bigger males were the ones claiming and holding territories.   The researchers also discovered that time didn’t have much to do with whether a damselfly male was territorial or not.  The wing length and weight of the wandering males was about the same and wandering males were consistently smaller than the territorial males on both days.  Wandering males made up about the same percentage of the population both days too.  So, the smaller males weren’t ever getting territories and were consistently being excluded.

The data that Koskimaki and colleagues presented in their paper suggest that the bigger, more physically impressive males get more mates.  To better understand the significance of these results, let’s consider a similar situation in humans that many people will recognize.  Think about what you know about stereotypical high schoolers.  Who gets more dates: the jocks (usually the bigger, more physically impressive males) or the nerds (usually the smaller, less physically impressive males)?  When I was in high school (I myself was firmly rooted in the nerd category!), the jocks got most of the girls while the nerds usually only admired the girls from afar.  The jocks outcompeted the nerds physically, and because they were generally more attractive, they excluded the nerds from finding dates by hogging all of the available girls.  If you ignore the possible confounding affects of wealth, intelligence, and overall personality that come into play in human mating behaviors, almost the same thing is happening in the high school students that we see in the damselflies that Koskimaki and colleagues studied!  In effect, the jocks among the damselflies were getting all the girls because they were better suited to protecting territories, and thereby attracted more mates, than the nerds who were unable to gain a territory.

I’ll end with two important questions: if it is so much better for males to be bigger so that they can more successfully hold valuable territories, 1) why are any males small and 2) why aren’t the damselflies getting bigger and bigger over time?  Koskimaki and colleagues suggest that that territorial and non-territorial males might form two distinct subgroups within the damselflies, each with their own strategies and goals for mating.  Even males without territories are able to mate with some females.  They could end up with the same number of offspring, thus ensuring the continued existence of smaller males in the population, if they have means for compensating for their relative lack of mating opportunities.  The team cites several other studies that suggest that this is happening in several territorial damselfly species, that non-territorial males are equally successful in producing offspring compared to territorial males.   It is likely that there are some benefits to being smaller or some costs to being larger that have not yet been accounted for.  Further studies in this area would be a great avenue for future research!

I hope you’ve enjoyed the dragonfly trilogy!  It’s been a lot of fun delving into the dragonfly literature for a few weeks and sharing information about my favorite group of insects.  I’m sure to post more odonate research in the future, but next time I’ll be telling a story of a centipede and a woman who is very, very scared of them – me!

Literature Cited:

Koskimaki, J., Rantala, M.J., & Suhonen, J. (2009). Wandering males are smaller than territorial males in the damselfly Calopteryx virgo (L.) (Zygoptera: Calopterygidae). Odonatoligica, 38 (2), 159-165.

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Text copyright © 2010 DragonflyWoman.wordpress.com

Dragonfly Territoriality (The Dragonfly Trilogy, Part Two)

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!

dragonfly habitat

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.

Anax junius patrolling

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.

Anax junius males in combat

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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Text and images copyright © 2010 DragonflyWoman.wordpress.com