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Epigenetics and Neoteny

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Epigenetics and Neoteny

Postby jpenhall » Thu Jun 17, 2010 9:11 am

am very interested in the taxonomy of birds, with particular reference to albatrosses.

I was struck by the fact that two related taxa have a cytochrome-b distance of 0.0000% between them, indicating that they diverged very recently.

They are Diomedea epomophora epomophora the “Southern” Royal Albatross and Diomedia epomophora sanfordi the “Northern” Royal Albatross.

In their juvenile plumage stage, the two birds are virtually identical, with upperwings black with very few traces of white. Thye differ slightly in terms of the extent of black flecking in their otherwise white mantle,sanfordi having slightly more.

In their adult plumage, nominate epomophora has largely white upperwings with a black trailing edge and black primaries. Sanfordi has largely black upperwings.

It struck me that the difference between them might be due to an epigenetic change: namely, that in the case of sanfordi, an epigenetic change has prevented or modified the development of the full adult plumage. And it is striking that the neotenous plumage is retained in the more northerly taxon.



This has wider application, because the of the 7 taxa involved in the Wandering Albatross Diomedea exulans complex, 6 of them show the preservation of neotenous features into adult plumage. The juvenile stage of nominate exulans shows the entire body and wings chocolate-brown. The immature stage of exulans shows some whitening on the rump, and white flecking on the mantle. The fully adult birds of exulans are very similar to the adult stage of nominate epomophora: namely wings white except for a black trailing edge and black primaries.

All colonies of nominate exulans breed on islands close to the Antarctic Convergence: Kerguelen Is, Crozet Is, Prince Edward I. with tiny populations on Heard I and Macquarie I.

All of the other taxa in the complex breed further north, and all show to a greater or lesser degree the preservation of part of the dark juvenile and intermediate plumages into adulthood. In the southern most of them, dabbenena,males have a plumage very like nominate exulans, retaining some brown colouring in the cap. Females retain much more of the dark plumage. The further north you go, the more both sexes retain dark plumages. It strikes me that these differences might well reflect epigenetics changes triggered by the different environments in which the birds live.

Does this sound plausible?

Many thanks for your thoughts.



Dr John Penhallurick

86 Bingley Cres

Fraser A.C.T. 2615

Australia

email:jpenhall@bigpond.net.au

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Please visit my website:http://www.worldbirdinfo.net
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Postby JackBean » Thu Jun 17, 2010 9:51 pm

the Cyt C is highly conserved. Even we share high percentage of homology with like pea's Cyt C. You can't say that just from one gene. You need the check the whole genome.
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Re: Epigenetics and Neoteny

Postby kolean » Fri Jun 18, 2010 7:39 pm

When you look at the whole genome, and notice that it is very highly conserved, and that the parts of the genome that varies is not for known coding genes, then you can speculate that is epigenetics.

Your idea does seem plausible, since epigenetics is used for regulation of timing in development. I would go on to speculate that the development of the plumage was halted, while the rest of the development into adulthood (sexual maturity) continued. And as you stipulated, that plumage was naturally selected to continue in the different environment (dominate epigenetic mutation?).
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Postby jpenhall » Sat Jun 19, 2010 12:16 am

Re Jack Bean's comment: I referred to the cytochrome-b gene, not to to cytochrome-c gene. The rate of mutation in the cytochrome-b gene is estimated to be ten times faster than that of nuclear genes. Thus it is particularly useful for sorting out closely related birds.
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Re: Epigenetics and Neoteny

Postby jpenhall » Sun Jun 20, 2010 11:52 pm

Dear Friends,
I have continued to reserach further the issue of genetics and albatrosses. I found a paper by Burg and Croxall (2004) "Global population structure and taxonomy of the Wandering Albatross species complex" Molecular Ecology 13: 2345–2355. This paper examines alleles in the mitochondrial control region. They found that some alleles were shared among certain taxa, while others were not. Based on the degree of sharing, they proposed to recognise all taxa in the compelx as "good" species, except for the pair Diomedea antipodensis and Diomedea gibsoni.
It occurred to me to wonder how common alleles were in the human genome. After all, humans are one species, no? Researching this with Google, I found a paper with the title “Allelic Variation in Gene Expression is Common in the Human Genome.” In other words, allelic variation does not prevent interbreeding. The fact there there were different rates of sharing for various alleles in taxa within the Diomedea exulans complex presumably means that they have diverged more or less recently, which is eactly what is shown in the phylogenetic tree. But this surely does not mean that we can equate allelic variation in a control region with inability to interbreed.

I also searched with “rates of evolution in mitochondrial control regions”. I found a website http://www.detectingdesign.com/dnamutat ... ochondrial
which stated: “Some of the mtDNA does not code for anything (thought to make these sections immune from "natural selection pressure"), and are known as the "control regions". One particular region appears to mutate faster than any other region (1.8 times faster), because the variation among humans is greatest here.

Thus I conclude that Burg and Croxall's paper does not demonstrate anything in relation to the species staus of Albatrosses.
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Postby JackBean » Mon Jun 21, 2010 4:11 pm

Sorry, my bad.
But still I think you need to look to more than just one gene ;)
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