[Odonata-l] Sexual Dimorphism

[Dennis Paulson]

Hi, Pam and all,

I think you have stated the situation clearly. In territorial  
anisopterans, it is thought that females choose oviposition sites,  
and the male who defends a good oviposition site is very likely to  
mate. I don't think there is any evidence that it occurs in the way  
Glenn described, notwithstanding that it sounds good, but we should  
keep an open mind about it. Probably many of you have seen male  
Perithemis (amberwings) fighting with one another to protect a small  
patch of water, and that patch of water usually contains one or more  
oviposition sites. A female comes into the general area, and the male  
immediately leads her to the oviposition site. It's the real estate,  
not the owner, that is the attractant, just as in so many birds, as  
you describe.

I don't know of any odonate that forms leks, in which multiple males  
get together and duke it out in a small space, and a female comes to  
that place and chooses a male. There are no manakin dragonflies.  
That, of course, could happen anywhere, as such a place would be  
chosen as a mating site, not an oviposition site (can you imagine the  
female trying to lay eggs with all those males present?). But there  
is so much we don't know about tropical odonates that I wouldn't be  
surprised to learn of yet-unknown mating systems.

In North America we don't have a lot of species in which males  
display to females. Calopteryx (jewelwings, demoiselles) damselflies  
are the best examples, and female choice must be important in that  
group. Even in the many odonates in which males don't display, but  
just grab any female they see, there is female choice, as a female  
taken in tandem doesn't have to go into the copulation wheel.  
However, from my experience, I would say the vast majority do so, so  
a male vigorous enough to attempt mating is probably satisfactory.  
Many odonates mate away from water, and those would be interesting to  
look at more closely, as in those cases, there is no "territory  
quality" entering into the picture, so one wonders if another sort of  
female choice might be exercised. In some places where Enallagma  
(bluets) were common, I've seen dozens and dozens of tandem pairs  
making their way down a road from the surrounding countryside to a lake.

The tropics are where you find dazzling displays by male odonates,  
mostly damselflies. There have been some good studies on some of  
these, but not nearly enough. Sometimes more than one male displays  
to a female at the same time. There are also fascinating situations  
in which some males (often more brightly marked ones) maintain  
standard territories to which females come, but others of the same  
species, often recognizably different, hang in the background and  
attempt to mate with females that come in to the territories of the  
dominant males. This also has parallels among birds.

Dennis

On Feb 8, 2007, at 7:28 AM, PAMELA HUNT wrote:

> Hi again,
>
> I'll admit being fairly new at this game, and at some point my bird
> analogies will run up against a wall, but it's worth considering that
> females are not necassarily chosing males but chosing territories
> (=oviposition sites). Glenn's verbal picture of S. hineana makes  
> this point
> nicely.  Is it the MALE the female is chosing or the spot of  
> sphagnum he has
> staked out?  Such an assumption has been made repeatedly with  
> birds, and
> much of the time a detailed study of female behavior has proven it  
> wrong
> (Bobolinks and Black-throated Blue Warblers come to mind). Males are
> fighting over their territories, so in the end one assumes that the  
> "better"
> male gets to better spot, so there is something of a correlation  
> between
> male quality and territory quality. Which is the female chosing?   
> Who knows,
> and I imagine that a detailed study of female behavior in odonata  
> would be a
> challange indeed.  But I'd be willing to go out on a theoretical  
> limb here
> and propose that the quality of an oviposition site trumps any  
> variation in
> how a given male might be perceived.  Of course, Glenn's S.  
> scudderi example
> might be a different system entirely, since oviposition wouldn't be
> occurring near the males' chosen rock in mid-stream.
>
> So on to a related question, could any odonata be considered to  
> form leks?
>
> Pam Hunt
> Penacook, NH
>
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-----
Dennis Paulson
1724 NE 98 St.
Seattle, WA 98115
206-528-1382
dennispaulson at comcast.net



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