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Eye color as a subspecies character. (1 Viewer)

jmorlan

Hmmm. That's funny
Opus Editor
United States
Eye color has been used as a taxonomic character diagnosing species, although usually (always?) combined with other characters. Eye color is often variable within species, changing with age or differing by sex. But are there any examples where intraspecific eye color varies geographically and might be used to diagnose previously undescribed subspecies?

My amateur understanding is that valid subspecies must differ in ways that can be detected in museum specimens, and that characters not visibly detectable (e.g. song dialects, genetic markers) cannot be used to diagnose valid subspecies.

Eye color is detectable only in living birds, not in specimens (other than perhaps by notes on the label). Just curious if eye color has been or could be used to describe valid subspecies.

Thanks.
 
Why should it not be possible to use song differences to describe subspecies when that in some instances is the main difference in defining species? (usually between previously described subspecies, but I think not always?)

Niels
 
Why should it not be possible to use song differences to describe subspecies when that in some instances is the main difference in defining species? (usually between previously described subspecies, but I think not always?)
Niels
My understanding is that such song differences are used to diagnose species only when they represent an isolating mechanism. The issue is not that the songs differ, but whether individuals of one species do or do not respond to playback. There are many cases where populations of one species have song dialects but those song differences are not reproductive isolating mechanisms and there is free gene flow between the song dialects.

My question is about eye color. If eye color is an isolating mechanism then the differing populations are biological species. But what about geographic variation where eye color is not established as a reproductive isolating mechanism? Can those populations be named subspecies?
 
Asio otus otus - orange-red eyes
Asio otus wilsonianus - yellow eyes

There may be other differences between these two, of course.
 
Eastern Towhee subspecies in the southeast are best differentiated by iris color (from red in north to pale yellow in south Florida.). Amount of white in tails also varies.
Andy
 
I don't think there is any rule that states that eye color can't be used to distinguish subspecies, although the norms in ornithology may not consider it all that important in taxonomy. Certainly there is no rule I am aware of requiring taxonomy to be based on features retained in museum specimens. In marine mammals at least coloration patterns are considered important and relevant, even though the standard for museum collections are bones, not skins.
 
Certainly there is no rule I am aware of requiring taxonomy to be based on features retained in museum specimens. In marine mammals at least coloration patterns are considered important and relevant, even though the standard for museum collections are bones, not skins.

It's not a rule about subspecies, it's a rule about the scientific method. My understanding is that scientific results need to be falsifiable to be valid. If the supposed features cannot be confirmed on further review, then the claims can and should be questioned. There is a whole literature that invalidates claimed subspecies based on the peer assessment that the supposed differences are caused by such things as differences in age, wear, sample size etc. rather than consistent geographic differences in size, color or pattern.

How does one falsify claims for which the original raw data has not been preserved?
 
How does one falsify claims for which the original raw data has not been preserved?

By examining additional specimens – presumably live ones, in your eye-colour example.

And if the species in question has gone extinct in the interim, well, that's just one of the limitations of a historical science like systematics.
 
How does one falsify claims for which the original raw data has not been preserved?

As in other observational sciences, by repeating the experiment. Or, if there is suspicion of cheating, by demanding to see original field notes from each of the days in the field.

Niels
 
To be valid, I think there must be a type specimen. If eye color is the only difference, the type and co-types would presumably have to be recently collected live birds. Do I have that right? Or could one select an older type specimen even if eye color is not known by basing it on geography? How does priority work when naming new subspecies in such cases?

Long-eared Owl and Eastern Towhee are good examples, but their subspecies also differ in other ways which are preserved in museum specimens. Another possible example that occurred to me is Red-eyed/Chivi Vireos but I think those are now split as separate species. Another example is Boat-tailed Grackle with four subspecies, two of which have light eyes and two have dark. In those cases, there are other differences but I'm not sure the differences are adequate for diagnosis without knowing the eye color.
 
To be valid, I think there must be a type specimen. If eye color is the only difference, the type and co-types would presumably have to be recently collected live birds. Do I have that right? Or could one select an older type specimen even if eye color is not known by basing it on geography? How does priority work when naming new subspecies in such cases?

Long-eared Owl and Eastern Towhee are good examples, but their subspecies also differ in other ways which are preserved in museum specimens. Another possible example that occurred to me is Red-eyed/Chivi Vireos but I think those are now split as separate species. Another example is Boat-tailed Grackle with four subspecies, two of which have light eyes and two have dark. In those cases, there are other differences but I'm not sure the differences are adequate for diagnosis without knowing the eye color.

I may be misunderstanding, but it seems as if you are assuming that eye color/pigment cannot be preserved, which is of course not the case. If someone were to catalogue a type specimen, I would think that they would preserve what they believed to be the key differentiating features - even if they were not captured in the standard "skin format" that are typical of collections.
 
I may be misunderstanding, but it seems as if you are assuming that eye color/pigment cannot be preserved, which is of course not the case. If someone were to catalogue a type specimen, I would think that they would preserve what they believed to be the key differentiating features - even if they were not captured in the standard "skin format" that are typical of collections.
Good to know. I have never seen eyes preserved in any of the museum collections I have visited. I have seen labels that had soft part colors noted, but those are not subject to verification. Also different people perceive colors differently and use different terms for the same color. E.g when presented with pale pink, typically half the people asked will claim that the color is pale yellow.
 
Good to know. I have never seen eyes preserved in any of the museum collections I have visited. I have seen labels that had soft part colors noted, but those are not subject to verification. Also different people perceive colors differently and use different terms for the same color. E.g when presented with pale pink, typically half the people asked will claim that the color is pale yellow.

I think the first part re verification would be a question of going to the same area and repeating the experiment (i.e., seeing the eyes of a bird). However, there is a problem in eye color seemingly being able to change pretty fast after the life is lost in the specimen - so older labels where the eye color was only looked at after the bird had been sacrificed might not be good descriptions. This is what I have understood from previous threads here in BF, not my personal experience.

Regarding what people call a color: there has been publications of color plates so that one should compare a given color to many printed samples and use the same color designation as the author used for the best fit. A taxonomic description should include the reference on which standard set of color plates had been used for the comparison.

Niels
 
Regarding what people call a color: there has been publications of color plates so that one should compare a given color to many printed samples and use the same color designation as the author used for the best fit. A taxonomic description should include the reference on which standard set of color plates had been used for the comparison.
But how were the "standard" color plates preserved? Printed color plates fade with time and such standards need to be archived to prevent exposure to the light. I have a copy of Smythe's "Naturalists Color Guide" published in 1975 by AMNH. It has color chips deposited by the McCorquodal deposition process on heavy cover stock. It uses opaque moderately glossy lacquers instead of standard printing ink which supposedly should make the colors last long. Each color is compared to Ridgway's standards. But the author admits that each color is only representative of a family of colors. It is not possible to resolve the fine difference between pale pink and pale yellow e.g. The only way I know to demonstrate that issue is with a color wheel with white at the center. Even though yellow and pink are separated by red, when one looks near the center of the wheel, the differences disappear to the human eye. Other issues involve the ambient light. E.g. colors look different in sunlight vs. various types of indoor lighting. A modern solution is a colorimeter or better yet, a spectrophotometer. To use these tools the specimen must be placed in a controlled environment for the color wavelengths to be measured. In most cases, doing so with a live bird is impractical.
 
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I suspected you ought to know these things but by the wording of your questions, I thought differently.

Best
Niels
 
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