[Odonata-l] zygopteran appendage shape

[Erland R. Nielsen]

Hello

On page 29 Corbet describes the so called Agrion or sentinel position of the male (upright vertical supported just by the appendages).
He writes:

"
This behaviour occurs commonly in Coenagrion and Platycnemididae, and also in Megapodagrionidae and Protoneuridae.
...
Adoption of the posture can be facultative (e.g. Erytrhomma, Schneider 1983), sometimes depending on the strenght of the wind (Rehfeldt 1991a). This posture can reduce the risk of predation by frogs because the upright male commands a wide view (Rehfeldt 1991a). It also provides a stronger attraction (than does a horizontal posture) to other conspecific tandems (Martens 1994a), enabling the attracting pair to enjoy the benefits of group oviposition. Other hypothetical benefits relate to enlarging the range of potential oviposition sites, preventing the males body from overheating, and presenting an effective physical obstacle to tandem-splitting attempts by single males (Martens 1994a).
"

My experience is that among the Coenagrion species I see in Denmark, only the C. puella tend to oviposite in sentinel position. I don't have that much knowlegde about the shapes of the appendages on Coenagrion, but in the new book : Field guide to the Dragonflies of Britain and Europe by Dijkstra, this is said about C. puella:
"
The wide gap between the upper appendages is unique among related species
"

So maybe this sentinel position may be related to the shape of the appendages, or I guess rather the shape of the linkage, as the females shape of the pronotum must influence.

Erland R. Nielsen
Kolding, Denmark
erland_refling at stofanet.dk
http://home1.stofanet.dk/erland_refling/danish_dragonflies.htm

  ----- Original Message ----- 
  From: Dennis Paulson 
  To: Odonata-l 
  Sent: Wednesday, December 06, 2006 10:38 PM
  Subject: [Odonata-l] zygopteran appendage shape


  Hello, odonatists.


  Bill Hull and I were just exchanging comments about and photos of various damselflies ovipositing in tandem, noticing how some of the males rest against the substrate and others are supported more or less vertically by the female. Species of Argia oviposit mostly in the open, often in current and where there would be nothing for the male to grasp. Enallagma much more often oviposit on emergent vegetation or floating vegetation in still water where the male can rest at water level. I speculate that the larger paraprocts (inferior appendages) of Argia could even be an adaptation to better prop the male upright in tandem. Enallagma have quite different paraprocts, usually pointed and slender rather than bulky and complex as in Argia. It seems reasonable that there is some mechanical difference in such different appendages. At the same time, in the few species of tandem-ovipositing Ischnura, I have not seen any upright males.


  It would be interesting to do a survey of tandem-ovipositing zygopterans to see how much variation there is in male position and if it correlates with appendage type. Lestes have a very different hookup, and I have never seen a female supporting a male as you see so often in the Coenagrionidae. In fact, I'm not sure I've seen that in any other family of zygopterans but Protoneuridae and Platycnemididae, in which males are supported much as in Argia. I wonder if this is the case in all species of the latter two families.


  I don't recall if Philip Corbet discussed this variable in his book, and I don't have my copy of it here right now.

  -----
  Dennis Paulson
  1724 NE 98 St.
  Seattle, WA 98115
  206-528-1382
  dennispaulson at comcast.net








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