[Odonata-l] color change in female E. geminatum

[Thomas Schultz]

Richard,

Oops, in checking my photo records the top two photos were of  
different tandems taken in the same hour of the same day.  Hence the  
"disappearance" of the mites.  But I think you get the idea of the  
color change.  Female before taken in tandem are structural blue but  
gradually lose it until the tan pigments are expressed by the end of  
copulation.

I think the change here is unlikely to be due to temperature of the  
female.  The body temperatures of lone females and those in tandem  
are unlikely to differ when they are in full sun in both cases.    
Females in tandem,  may in fact, have elevated temperatures when they  
are stationary and unable to lose heat by convection or postural  
changes.

The blue of Enallagma civile (and Anax junius) has been shown to not  
be due to Tyndall scattering as was once thought, but due to coherent  
scattering and interference from an array of nanospheres in the  
endoplasmic reticulum of the epidermis (Prum et al. 2004, J  
Experimental Biology 207: 3999-4009).  These spheres of unknown  
composition are much larger than the particles that would cause non- 
coherent Tyndall scattering.  In Veron et al.  (1974) the loss of  
blue in several damselflies was attributed to pigment vesicles moving  
from the proximal to the distal side of the epidermal cells,  but  
they had the physics of the structural blue color incorrect.

It is pretty likely that the color change than one observes in death  
or when chilled is due to such a reorientation of pigments and  
nanospheres, but I think this color change in E. geminatum females  
and Argia apicalis is not passive but under physiological control.

Yours,

Tom

Tom D. Schultz, Ph.D.
Professor of Biology
Denison University
Granville, OH 43023
740-587-6218
schultz at denison.edu



> Thomas Schultz wrote:
>> Dear All,
>> I tried to send this message before but it didn't come back to me  
>> so I concluded that it didn't go through.  I apologize if this is  
>> redundant.
>>
>> Has anyone else noticed that females of /Enallagma geminatum/  
>> change their color during copulation?  I am aware of "voluntary"  
>> color change in male /Argia apicalis/, but not in any female / 
>> Enallagma/.
>>
>> In the three photos, the top two are of the same tandem before and  
>> during copulation.  The lower photo is of a different tandem after  
>> copulation.  I have also seen many ovipositing females that have  
>> lost their andromorphic coloration.
>>
>>
>> Tom
>>
> The blue is almost certainly the result of tyndal scattering (it's  
> the right colour). Hence migration inwards of the scattering  
> particles will change the shade. Something similar happens in  
> Austrolestes species (there is a Veron paper from 1973 on this).   
> In Austrolestes this colour shift is associated with the thermal  
> environment. Males are dull in the morning until they get up to  
> temperature, females are dull, but can become brightish blue if  
> they are in a hot, sunny environment for any length of time (e.g.  
> sometimes when egg laying).  Your female may be getting cold while  
> she is immobile.
>
> What happened to the two mites on the female's abdomen in the top  
> photograph (absent in the late wheel photo below,
>
> Richard
>
> -- 
> Dr Richard Rowe
> Zoology & Tropical Ecology
> School of Tropical Biology
> James Cook University
> Townsville 4811
> AUSTRALIA
>
> ph +61 7 47 81 4851
> fax +61 7 47 25 1570
> JCU has CRICOS Provider Code 00117J

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