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

[Thomas Schultz]

This is the response I sent out on July 22 my to Richard's initial  
reply about the geminatum color change.

> 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
>
>




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