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

[Dennis Paulson]

The color change in female Enallagma geminatum could be the same as  
occurs in males of several species of Argia (apicalis, sedula) that  
turn entirely or partially gray in normally blue areas when in  
tandem. Subduing the blue coloration would seem to make them less  
conspicuous and could be to avoid the attention of predators and/or  
other males. No reason this couldn't happen in andromorphic (blue)  
females, although it's the first I know of in Enallagma.

The situation in Argia translata, a widespread species of the  
neotropics and eastern North America, is especially interesting.  
Mature males have a dark thorax and abdomen (variable but small  
amounts of blue on the tip), but when in tandem the thorax becomes  
vividly striped (that to me makes them MORE conspicuous, unlike the  
situation in the other Argia and female E. geminatum). Whatever it is  
that makes the sides and antehumeral stripes of the thorax dark gray  
in mature males is apparently reversible, as those areas in tandem  
males are pale tan, just as in the female (and younger males). Both  
the ultimate and proximate factors involved in these changes are very  
worthy of attention.

Dennis

On Jun 25, 2007, at 6:35 AM, Thomas Schultz wrote:

> 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
>>

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



-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailweb.ups.edu/pipermail/odonata-l/attachments/20070625/84e2faa9/attachment-0001.html