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Discussion on Bird Morph and Phenotype


MacMe
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Earlier today I posted on the ID forum a bird with a white morph and it got me thinking and wanting to know your thoughts on the topic.  For the sake of the argument I'll refer to the Reddish Egret and its white morph since that was the animal that started these thoughts. 

I am assuming the white morph individual is genetically hardwired this way and will always display this phenotype.  Since coloration is so important to birds, how does being white impact their mating success?  I would assume the white morph is selected against, meaning they simply don't attract mates, or perhaps an underlining condition that comes with this coloration that inhibits or reduces reproductive success. 

Another way I was thinking about this is maybe both Reddish Egret phenotypes have no issue pairing with each other.  If so, do they have issues with cross breeding?  To my human eyes, white morphs look similar enough to Great Egrets and to Snowy Egrets to merit this idea.

I am also assuming the white morph is a homozygous trait, meaning it comes from both parents.  If either parent supplies the red phenotype then the offspring will be red as well.

Anyone know more about this?  What color are the chicks from two white morph parents? What is the reproductive success of the white morphs.  How successful are white morphs at catching food and avoiding predators?  Are these questions moot in reference to this species?  

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14 hours ago, MacMe said:

Since coloration is so important to birds, how does being white impact their mating success?

Depending on the species and morph, the bird may not survive long enough to mate.  White animals are often easy prey.

14 hours ago, MacMe said:

If so, do they have issues with cross breeding?  To my human eyes, white morphs look similar enough to Great Egrets and to Snowy Egrets to merit this idea.

I don't know what factors beyond appearance attract mates.  It may be that potential mates attracted initially by appearance are then deterred by scent, behavior, or other characteristics.

Interesting topic, even if all I can contribute is my ignorance.  It may be better suited for the 'General Birding Topics' forum.

Edited by Charlie Spencer
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2 hours ago, Charlie Spencer said:

Depending on the species and morph, the bird may not survive long enough to mate.  White animals are often easy prey.

Good point.  Though there are many all white bird species and they seem to do well.  The differenece would be that those all white species are adapted to being all white, where as the Reddish Egret White Morph is not.  Being white probably makes it harder to get food as well.  Perhaps the strategies they use in their Reddish morph does not translate as well to the white morph

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3 minutes ago, MacMe said:

Though there are many all white bird species and they seem to do well.

Let's downsize.  While we started with relatively large wading birds, there are plenty of smaller creatures that are easier to capture.  White alligator hatchlings aren't that uncommon but few to none survive in the wild to adulthood.

Although birds' eyes see colors ours don't, so maybe what looks like plain white to us has added subtleties for birds?

Edited by Charlie Spencer
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5 minutes ago, Charlie Spencer said:

White alligator hatchlings aren't that uncommon but few to none survive in the wild to adulthood.

I suppose albino individuals would have similar results, but albinoism is more than just being white.  I don't think the reddish egret's white morph is albinoism.  I did a quick check on all-white bird chicks, American White Pelican, and Snowy and Great Egrets, and those all have white chicks. White Ibis juveniles are not mostly white.  Gator hatchlings after leaving mom have more time to spend getting to adulthood, whereas all-white bird chicks have a relatively shorter time.  This may allow all white bird chick to exist.  Anyone know of an all, or mostly-white adult bird with non-white chicks?  How long does it take these to reach adulthood?

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3 hours ago, Charlie Spencer said:

White animals are often easy prey.

Another though about this is animals often make themselves easier prey to show how fit they are. Bright and obvious coloring, loud or overt behavior, and ornate features that inhibit motion are some examples

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I don't have any answers but I can add to the confusion with a few more questions. If a white morph Reddish Egret is said to be at a higher risk of being preyed upon than a regular morph, would that translate to say that white herons and egrets are generally preyed upon more than their colourful cousins in the heron/egret family? As an example, are Great Egrets at more risk of predation because they're white than Great Blue Herons are? 

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Not a biologist, but... if the polymorphism is stable, I think neither morph could cause a significant disadvantage on the whole.  You might be interested in https://en.wikipedia.org/wiki/Polymorphism_(biology) and https://en.wikipedia.org/wiki/List_of_polymorphisms.  The latter discusses what's known about what keeps each polymorphism going.  Usually in polymorphic species, the morphs mate with each other freely.  (The White-throated Sparrow is an exception; the polymorphism is stable because birds prefer to mate with the other morph.)

Western Reef Herons and Little Egrets have a dark morph as well as a white one.  (In Little Egrets the dark morph is rare.)  Great Blue Herons have a white(ish) subspecies, and Snow Geese have a mostly white and a mostly dark morph.  In Ross's Geese the dark morph is rare.

In addition to White Ibises, Little Blue Herons are dark as juveniles and white as adults.

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25 minutes ago, Jerry Friedman said:

Usually in polymorphic species, the morphs mate with each other freely

Going back to the original question, being white probably doesn't affect sexual preference, and if it does, it is selected for.  But hunting success and predator avoidance could still have significant effects.  Could we include temperature regulation as well?

 

2 hours ago, Charlie Spencer said:

Although birds' eyes see colors ours don't, so maybe what looks like plain white to us has added subtleties for birds?

1 hour ago, lonestranger said:

If a white morph Reddish Egret is said to be at a higher risk of being preyed upon than a regular morph, would that translate to say that white herons and egrets are generally preyed upon more than their colourful cousins in the heron/egret family?

Both of these quoted questions are very interesting

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3 hours ago, MacMe said:

Going back to the original question, being white probably doesn't affect sexual preference, and if it does, it is selected for.  But hunting success and predator avoidance could still have significant effects.  Could we include temperature regulation as well?

Here's an article on hunting success suggesting that for Reddish Egret, white plumage improves success in hunting for prey in deep water.  https://www.jstor.org/stable/4132635

On temperature regulation, now that you mention it, it is interesting that the species that stick around in winter tend to have dark plumage (at least here in New Mexico).

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3 minutes ago, Jerry Friedman said:

Here's an article on hunting success suggesting that for Reddish Egret, white plumage improves success in hunting for prey in deep water.  https://www.jstor.org/stable/4132635

This abstract is very interesting. The dark-plumaged birds foraging in shallow water (1-5cm) tend to use active tactics.  Allaboutbirds describes Reddish Egrets as active hunters, so that seems to fit.  The abstract also says the white morphs spent more time in intermediate depths (5-10cm) then their reddish counterparts while actively foraging.  I didn't know white was a better color for deeper water.

Its likely this trend fits to other white shorebirds.  Allaboutbirds' description of Snowy Egrets sound like it use active tactics while its description of the Great Egret sounds more passive.  Now it makes me think about Great Blue Herons.  How deep do they forage?  If they follow this hypothesis, they would stay fairly shallow, despite their long legs.  

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What I gather from everyone's contribution is polymorphism is a trait that helps the success of the species. 

1) It keeps the species from dying out from a slow or sudden change in their niche, because the other morph may be better in this new situation.  The morph ratio may shift but the species will survive.  An example of this are those white moths in the UK that were no longer camouflaged when the soot from the coal factories turned the white-trunked trees grey.  The population shifted to the grey morph moths.  Then, when environmental laws were placed and the trees became white again, the grey morph wasn't cutting it anymore and the moth population shifted back to white. 

2) It helps the species gain the maximum population range.  When the environment shifts from one type to another it may favor the other morph extending the range of suitable habitat.  It makes me wonder which niche white alligators fill and if there was ever a time where that morph was the more successful.

3) It makes me wonder about species without apparent polymorphism. However, polymorphism also effects traits that aren't readily noticeable.  So, a species with only one color morph may not be as vulnerable to changes as it may seem.  With this said, it sounds like the more morphs the better.  I assume this isn't true, that there is a detrimental effect with having multiple morphs that get compounded the more a species has.  I wonder what the 'happy medium' is and if all stable species is at this value.

4) These below questions merit further exploration

On 1/13/2022 at 10:39 AM, Charlie Spencer said:

Although birds' eyes see colors ours don't, so maybe what looks like plain white to us has added subtleties for birds?

On 1/13/2022 at 11:02 AM, lonestranger said:

If a white morph Reddish Egret is said to be at a higher risk of being preyed upon than a regular morph, would that translate to say that white herons and egrets are generally preyed upon more than their colourful cousins in the heron/egret family?

Have any of you come to any other conclusions?

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13 minutes ago, MacMe said:

What I gather from everyone's contribution is polymorphism is a trait that helps the success of the species. 

I'm not sure how you got that from my comments, but I disagree.

13 minutes ago, MacMe said:

1) It keeps the species from dying out from a slow or sudden change in their niche, because the other morph may be better in this new situation.

Or it's a genetic leftover from when the morph was better suited, but has been abandoned under current circumstances in favor of the dominant trait.  Or the morph never was or will be preferable. Ma Nature doesn't need reasons to toss some oddball genes in the mix.

Edited by Charlie Spencer
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@Charlie Spencer please expound on why you disagree.  You can't just dangle an carrot and walk away!

Ma Nature can put some weird things in the mix but she also is good and getting rid of unnecessary things.  A rare polymorphic trait lingers because the organism with the gene is successful enough to pass it on to the next generation.  Either the trait helps in some way, or it isn't 'bad' enough to be fully removed

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54 minutes ago, MacMe said:

@Charlie Spencer please expound on why you disagree.  You can't just dangle an carrot and walk away!

I'm sorry, I thought my next paragraph explained my disagreement.  I don't see anything in your statements that support morphs being favorable, at least, nothing that can't also support the reverse.

54 minutes ago, MacMe said:

Ma Nature can put some weird things in the mix but she also is good and getting rid of unnecessary things. 

Again, I disagree.  Nature is good at getting rid of UNSUCCESSFUL things.  Unnecessary ones that aren't detrimental to survival and breeding are often ignored and retained.  Look at male nipples, for example.

Edited by Charlie Spencer
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My apologies too, I thought those were two different thoughts

For favorable: The article about the Reddish Egret morph hunting.  The white morph allows the species a broader foraging range. I would assume other species, such as house cats, will exhibit varying hunting success and strategies due to coat color/pattern. The article listing different types of polymorphism implied to me that the variety (such as human blood type) will help prevent a species wide disaster in case one morph is no longer successful (I agree with you 'unsuccessful' is a more appropriate word than 'unnecessary').  In my moth example, the dark morph kept the species from going extinct in the industrial age, and again with the white morph when the air cleaned up.  Sexual dimorphism is another example found all over the world: one gender larger, or more colorful, or drab, etc. than the other.

Unfavorable: the morph leads to less success, like with the white alligator.  If the trait is completely removed and the environment changes enough to now favor that missing trait, that species essentially lost one of its tools.  Getting it back may take a very long time.  However, I am curious to postulate potential scenarios where a white gator would have better success.

It's possible that these benefits are indirect, happy little accidents, so to speak, only available because having those traits did not scientifically reduce the owner's reproductive success rate.  Although, I wouldn't discount 'unnecessary' completely, especially when comparing vestigial organs with organs that are completely absent.  One example would be those blind and transparent cave salamanders.  Eyes and skin tone are quite unnecessary in those caves.  To my knowledge, having them wouldn't not impact their success.  The unnecessary was removed to free up energy and resources.

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