[Odonata-l] Sexual dimorphism

[PAMELA HUNT]

My turn to chirp in on this (bird pun intended),

I think we also need to consider some of the OTHER theories put forth to 
explain sexual dichromism (to use Nick's excellent term!) in birds.

So far we seem to have been talking a fair bit about predation and a little 
about male-female mate choice (especially in regard to species with 
polymorphic females).  I'd be willing to extend the female crysis argument 
to cover those species with enophytic oviposition, where they are "sitting 
ducks" for a certain period of time.  Any crysis advantage there would be 
very beneficial (bearing in mind Nick's point that crypsis to us may NOT be 
crypsis to a predator).  For all we know, continued crypsis in females of 
libellulids is an evutionary carryover.  Never forget the neutral 
hypotheses!

As for males, cases of more extreme dichromism (e.g., Calopteryx, Libellula, 
etc.) might be driven by male-male competition, with the females caring 
less.  Species that are more territorial may benefit by signals that are 
easy to perceive in competitors.  Here's another "simple" experiment (as 
done with Red-winged Blackbirds): take a striking species like L. pulchella 
and somehow eliminate the bright white wing markings - making males look 
more female like.  What happens to these guys?  Do they fail to keep control 
or their stretch of shoreline, get fewer mating attempts, etc?

This is a fascinating discussion - keep those ideas coming!

Pam Hunt
Penacook, NH