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Author Topic:   Two species of crow evolving ...
RAZD
Member (Idle past 1633 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 1 of 14 (850359)
04-06-2019 3:56 PM


quote:
Two Species of Crow Are Evolving Before Our Eyes in Europe
MICHELLE STARR
29 MAR 2019
Two European crows that look quite different from each other are actually diverging from a single species, right before our eyes. In Western Europe, it's the inky-black carrion crow (Corvus corone). In the east, the grey hooded crow (C. cornix).
They overlap in a very narrow zone running along the River Elbe in Germany, where they sometimes mate with each other to produce fertile hybrids - a strange result, since many species hybrids are infertile.
Now, genomic analysis has revealed that C. corone and C. cornix are actually almost indistinguishable from a genetic standpoint. The only significant genetic difference between them can be found in the gene responsible for colouration.
"Defining speciation as the buildup of reproductive isolation, carrion crows and hooded crows are in the process of speciation," said evolutionary biologist Jochen Wolf of Ludwig-Maximilians-Universitt in Munich.
Exactly what was keeping the two populations apart was unclear - so Wolf and his colleagues performed genetic analyses of around 400 birds. These were selected from within the hybrid zone, as well as the zones on either side, where the species' territories don't overlap.
"Only two major effect genes which together encode the feather colour differ sharply on either side of the hybrid zone - the gray alleles are not found to the west of the zone and the black allele is absent in the eastern region," Wolf said.
"That's a very strong indication that there is rigorous selection on the basis of colour."
This suggests the crows are choosing mates based on colour. Birds of a feather literally, in this instance, flock together - carrion crows prefer black mates and hooded crows prefer grey ones.
Sexual selection.
Enjoy

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Replies to this message:
 Message 3 by Tanypteryx, posted 04-06-2019 6:33 PM RAZD has replied
 Message 4 by Faith, posted 04-06-2019 6:38 PM RAZD has seen this message but not replied

  
RAZD
Member (Idle past 1633 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


(1)
Message 10 of 14 (850398)
04-07-2019 6:58 AM
Reply to: Message 3 by Tanypteryx
04-06-2019 6:33 PM


I didn't come to appreciate sexual selection as a mechanism of evolution separate from natural selection until I read The Evolution of Beauty: How Darwin's Forgotten Theory of Mate Choice Shapes the Animal World”And Us by Richard O. Prum.
My pet theory is that sex is what has lead to increased intelligence in humans via more and more complex mating displays/rituals/song and dance.
I also see sexual selection as a mechanism for creating stasis in a breeding population in a stable ecology.
Mate selection operates at every mating opportunity, and thus can operate at a faster rate than other forms of natural selection in causing or suppressing changes to the breeding population.
See Sexual Selection, Stasis, Runaway Selection, Dimorphism, & Human Evolution
Enjoy

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Replies to this message:
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RAZD
Member (Idle past 1633 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 12 of 14 (857056)
07-05-2019 8:29 AM
Reply to: Message 10 by RAZD
04-07-2019 6:58 AM


More information on the "speciation in progress"
From A test for claimed knowledge of how macroevolution occurs, Message 705:
quote:
Defining a species
... Hooded crows and carrion crows look different, and largely mate within their own groups ” but in some areas, they hybridize. Should they be considered the same species or separate species?
If two lineages of oak look quite different, but occasionally form hybrids with each other, should we count them as different species? There are lots of other places where the boundary of a species is blurred. It's not so surprising that these blurry places exist ” after all, the idea of a species is something that we humans invented for our own convenience!
Classification is for our use in discussions, and they are subject to change when information provides new insights.
quote:
Carrion Crow: Distribution and genetic relationship to hooded crows
The carrion crow (Corvus corone) and hooded crow (Corvus cornix, including its slightly larger allied form or race C. c. orientalis) are two very closely related species[7] whose geographic distributions across Europe are illustrated in the accompanying diagram. It is believed that this distribution might have resulted from the glaciation cycles during the Pleistocene, which caused the parent population to split into isolates which subsequently re-expanded their ranges when the climate warmed causing secondary contact.[8][9]
A map of Europe indicating the distribution of the carrion and hooded
crows on either side of a contact zone (white line) separating the two species
Poelstra and coworkers sequenced almost the entire genomes of both species in populations at varying distances from the contact zone to find that the two species were genetically identical, both in their DNA and in its expression (in the form of mRNA), except for the lack of expression of a small portion (<0.28%) of the genome (situated on avian chromosome 18) in the hooded crow, which imparts the lighter plumage colouration on its torso.[8] Thus the two species can viably hybridize, and occasionally do so at the contact zone, but the all-black carrion crows on the one side of the contact zone mate almost exclusively with other all-black carrion crows, while the same occurs among the hooded crows on the other side of the contact zone.
It is therefore clear that it is only the outward appearance of the two species that inhibits hybridization.[8][9] The authors attribute this to assortative mating (rather than to ecological selection), the advantage of which is not clear, and it would lead to the rapid appearance of streams of new lineages, and possibly even species, through mutual attraction between mutants. Unnikrishnan and Akhila propose, instead, that koinophilia is a more parsimonious explanation for the resistance to hybridization across the contact zone, despite the absence of physiological, anatomical or genetic barriers to such hybridization.[8]
Also see Two species of crow evolving ... on this possible crow speciation in process, apparently due to coloration:
quote:
"Only two major effect genes which together encode the feather colour differ sharply on either side of the hybrid zone - the gray alleles are not found to the west of the zone and the black allele is absent in the eastern region," Wolf said.
Breeding populations apparently separated by sexual/mate selection.
quote:
Koinophilia is an evolutionary hypothesis proposing that during sexual selection, animals preferentially seek mates with a minimum of unusual or mutant features, including functionality, appearance and behavior.[1][2][3][4][5][6] Koinophilia intends to explain the clustering of sexual organisms into species and other issues described by Darwin's Dilemma.[3][4][5] The term derives from the Greek, koinos, "common", "that which is shared", and philia, "fondness".
Natural selection causes beneficial inherited features to become more common at the expense of their disadvantageous counterparts. The koinophilia hypothesis proposes that a sexually-reproducing animal would therefore be expected to avoid individuals with rare or unusual features, and to prefer to mate with individuals displaying a predominance of common or average features. ...
This Koinophilia is similar to what I proposed for sexual selection in Sexual Selection, Stasis, Runaway Selection, Dimorphism, & Human Evolution and my discussion on the causes of stasis in breeding populations living in stable ecological habitats.
This Crow mate selection is similar to the overlap of the end of ring species like the Greenish Warbler, another place where the definition of species is problematic.

we are limited in our ability to understand
by our ability to understand
RebelAmerican☆Zen☯Deist
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This message is a reply to:
 Message 10 by RAZD, posted 04-07-2019 6:58 AM RAZD has seen this message but not replied

  
RAZD
Member (Idle past 1633 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 13 of 14 (857059)
07-05-2019 8:45 AM
Reply to: Message 7 by Faith
04-06-2019 10:55 PM


observations vs "evo theory"
Of course. The black feathered population has more alleles for black feathers, and probably lots of homozygosity for black feathers at the feather loci too, while the grey population has more alleles for grey feathers and the same genetic situation. The black feathered population has correspondingly fewer alleles for grey feathers, which will eventually decrease to zero as reproductive isolation continues, and the grey population for black feathers. This ought to be elementary my dear Watson, but evo theory manages to complicate the simplest things.
What is complicated in this by "evo theory" when they are saying the same thing?
And of course it makes sense to categorize sexual selection as a type of natural selection, just as I've argued that geographic isolation is a form of natural selection too, as it isolates some particular collection of alleles and breeds them together to produce a new phenotype, which is all any selective process does.
Indeed, but sexual/mate selection explains observations that seem to be at odds with survival (peacocks) and why populations tend towards stasis in stable ecological environments/habitats.
And again, all this is within microevolution, it's ridiculous to make the arbitrary fact that the two populations don't interbreed into "speciation." It's nothing but two variations that happen to separate, and may possibly have a genetic barrier to interbreeding although that is not necessary. ...
Of course it is microevolution -- that's where all evolutionary change occurs, within the breeding population/s. Macroevolution is just microevolution over many generations with the accumulation of changes making descendant populations different from ancestral populations.
Speciation is one of the observed elements of macroevolution when two daughter populations are isolated over generations, allowing different microevolutionary paths to be taken by the daughter populations until they differ from one another. The crows are evidence of this difference in results of microevolution over generations.
Lack of interbreeding is the definition of species, so when this happens it is logical to call that a speciation event.
... If it does it could be because of the greater homozygosity of the characteristic feather color in each population and the more fixed loci each has the less ability to combine the two.
Indeed, the two populations have diverged from one another genetically, and this has resulted in the apparent speciation event in progress.
Whether you like it or not, this is how biology defines species and speciation events.
Enjoy

we are limited in our ability to understand
by our ability to understand
RebelAmerican☆Zen☯Deist
... to learn ... to think ... to live ... to laugh ...
to share.


Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)

This message is a reply to:
 Message 7 by Faith, posted 04-06-2019 10:55 PM Faith has not replied

  
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