[Odonata-l] Sexual dimorphism question?

Tue Feb 6 01:27:15 PST 2007

Hi Carlo,
Actually, female-based polychromatism has also been reported for Aeshnidae, 
but it seems to be a rare phenomenon (if I remember well, a photo of an 
androchrome female Aeshna affinis has been published in the Dutch dragonfly 
field guide by Wasscher & Bos).

Indeed, the frequency explanation may not be the sole reason behind the 
coexistence of several colourmorphs, but untill now, this seems the most 
plausible. However, other hypothesis must certainly not be excluded. Maybe 
someone on the list can mention the most important ones...

To be honest, I do not really see the problem of dull vs bright coloration 
in I. elegans. The observation that there are females that do look like 
males and some that clearly do not, still stands, and I guess it may be 
difficult -if not impossible- to judge brightness/dullness as a human being, 
while all that matters is the damselflies' observation ;) . Maybe a small 
difference in coloration is already enough.
By the way, in the light of your remark, it is interesting to note that much 
of the research on females-based polychromatism has focused on this species 
(as well as other Ischnuran species) and Ceriagrion tenellum - species in 
which an obvious dull vs bright contrast doesn't seem to apply either...

Another problem in applying the female-based polychromatism in explaining 
sexual dimorphism is that it is unclear if the occurence of andochrome 
females is a plesiomorph character or not (someone?). I guess the same 
applies to your hypothesis whether about bright males vs dull females.

you wrote:
>However I realise that the problem is not easy to solve and probably the 
>evolution of dragonfly coloration has followed several different pathways.

I totally agree!

All in all, an interesting subject!!
Cheers, rob

>From: "Carlo Utzeri" <carlo.utzeri at uniroma1.it>
>To: <odonata-l at listhost.ups.edu>
>Subject: Re: [Odonata-l] Sexual dimorphism question?
>Date: Mon, 5 Feb 2007 13:34:51 +0100
>
>Rob,
>the point, as you make it, is somewhat complicated, because female
>polychromatism was so far reported in just some zygopterans. But the
>frequency explanation advantage you recall might not be the only valid
>explanation. For example, in Ischnura elegans in central Italy, while the
>androchrome females are much more abundant than the gynochromes (154 vs
>104), in experimental insectaries males show a strong preference for the
>latter (87% of total matings). However in this species the male is
>relatively inconspicuous and I would not quote it as a good example of
>sexual colour-based dimorphism, as far as this must be based on bright vs
>dull coloration. Besides, the Zygoptera usually perch among vegetation,
>which makes them even less visible.
>My previous answer concerned the libellulids in general, in which commonly,
>males are more or less strongly aposematic while females show a
>greysh-yallowish coloration that appears relatively uniform across the
>entire family. So the question may be: why only males evolved specific
>bright coloration? It does not seem that females need to recognise their
>males by their colours, because almost never the males exhibit them to
>females prior to copulation. Thus possibly the male coloration did not
>evolve in the context of sexual selection. The unprofitable prey model
>hypothesis (my previous answer) is just an alternative explanation, which
>still needs strong experimental support. However I realise that the problem
>is not easy to solve and probably the evolution of dragonfly coloration has
>followed several different pathways.
>Greetings
>Carlo Utzeri
>
>----- Original Message -----
>From: "Rob van Bemmelen" <ixobrychus at hotmail.com>
>To: <mipilon at nrcan.gc.ca>; <odonata-l at listhost.ups.edu>
>Sent: Monday, February 05, 2007 11:26 AM
>Subject: Re: [Odonata-l] Sexual dimorphism question?
>
>
> >
> > I have a little guess:
> > Cryptic colored females may be less easily detected by males and thus 
>less
> > often harassed.
> >
> > Female-based colour-polymorphism (or polychromatism), in which there is
> > always one male-like female, has been explained by frequency-dependent
> > advantage, as males only get to learn to recognize male-like females 
>once
> > they become more abundant. This shows that the rare colourmorph is 
>always
> > in
> > advantage of the other. Thus, both a cryptic or a male-like appearance
> > have
> > advantage(s).
> >
> > However, this does not explain the bright coloration of males......
> >
> > I hope somebody else has a better answer...
> >
> > Cheers, Rob
> >
> >
> >
> >
> >>From: "Pilon, Michel" <mipilon at nrcan.gc.ca>
> >>To: <odonata-l at listhost.ups.edu>
> >>Subject: [Odonata-l] Sexual dimorphism question?
> >>Date: Sun, 4 Feb 2007 16:10:23 -0500
> >>
> >>Hello again,
> >>
> >>I hope I don't annoy all of you with my naive questions...
> >>
> >>After reading the answers about my id's request and considering that in
> >>both case the sexual dimorphism is important, I would like to ask you 
>the
> >>following question which came to my mind:
> >>
> >>What justify that sexual dimorphism amongst dragonflies...?
> >>
> >>With birds we know that the female is attracted by the colorful male and
> >>that she has to be duller because she has to lay over the eggs and 
>should
> >>not be seen by predators...
> >>
> >>Is it the same thing amongst Odonata? Does the female attracted by the
> >>male
> >>colors? And why usually are they duller than the male? (I'm thinking 
>also
> >>of Sympetrum obtrusum (white-faced Meadowhawk))
> >>
> >>Excuse-me again for my maybe so naive question...
> >>
> >>Michel Pilon
> >>Sherbrooke
> >>Quebec Canada
> >>
> >>Mes Parcours Nature:
> >>http://parcours.pilonm.org
> >>
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