Saturday, February 25, 2006

 

[evomech] Genetic assimilation of an acquired character (Classic Paper)

Genetic assimilation of an acquired character

[Waddington, Evolution, Jun '53]

Introduction

Under the influence of natural selection development tends to become canalized so that more or less normal organs and tissues are produced even in the face of slight abnormalities of the genotype or of the external environment (Waddington, 1940).

It has been suggested that if an animal is subjected to unusual circumstances to which it can react in an adaptive manner, the development of the adaptive character might itself become so far canalised that it continued to appear even when the conditions returned to the previous norm (Waddington, 1942). This mechanism would provide a means by which an "acquired character" in the conventional sense could be "assimilated" by the genotype, and eventually appear comparitively independent of any specific environmental influence.

Schmalhausen (1947) has independently suggested a very similar process, which he has discussed at some length under the name "stabilising selection"; a phrase which, however, he uses in a number of different senses, as Simpson (1947) has pointed out.

Full text at:

http://wwworm.biology.uh.edu/evodevo/lecture3/waddington53.pdf

John Latter

Model of an Internal Evolutionary Mechanism:
http://members.aol.com/jorolat/index.html

technorati tags: , , , , , ,

Please Note: If you are reading this in a Blog then replying directly to this message (as opposed to making a 'blog comment') requires membership of the 'Evolution: Where Darwin meets Lamarck?' Egroup at:
http://groups.yahoo.com/group/evomech/


Add to: CiteUlike | Connotea | Del.icio.us | Digg | Furl | Newsvine | Reddit | Yahoo


Friday, February 24, 2006

 

[evomech] Dollo's law and the re-evolution of shell coiling (Royal Society of London)

[Collin & Cipriani, Proceedings of the Royal Society of London B , Dec '03]

Abstract:

Gastropods have lost the quintessential snail feature, the coiled shell, numerous times in evolution. In many cases these animals have developed a limpet morphology with a cap-shaped shell and a large foot. Limpets thrive in marginal habitats such as hydrothermal vents, the high-energy rocky intertidal areas and fresh water, but they are considered to be evolutionary dead-ends, unable to re-evolve a coiled shell and therefore unable to give rise to the diversity seen among coiled snails. The re-evolution of a coiled shell, or any complex character, is considered unlikely or impossible (Dollo's law) because the loss of the character is followed by the loss of the genetic architecture and developmental mechanisms that underlie that character. Here, we quantify the level of coiling in calyptraeids, a family of mostly uncoiled limpets, and show that coiled shells have re-evolved at least once within this family. These results are the first demonstration, to our knowledge, of the re-evolution of coiling in a gastropod, and show that the developmental features underlying coiling have not been lost during 20-100 Myr of uncoiled evolutionary history.This is the first example of the re-evolution of a complex character via a change in developmental timing (heterochrony) rather than a change in location of gene expression (heterotopy).

Full text at:

http://striweb.si.edu/publications/PDFs/Collin_Dollo's%20Law%20Print%20version.pdf

John Latter

Model of an Internal Evolutionary Mechanism
http://members.aol.com/jorolat/index.html

technorati tags: , , , , , , , , , , , , , ,

Please Note: If you are reading this in a Blog then replying directly to this message (as opposed to making a 'blog comment') requires membership of the 'Evolution: Where Darwin meets Lamarck?' Egroup at:
http://groups.yahoo.com/group/evomech/


Add to: CiteUlike | Connotea | Del.icio.us | Digg | Furl | Newsvine | Reddit | Yahoo


Thursday, February 23, 2006

 

[evomech] Re: Birds that make teeth (Press Release + Summary)

>http://www.current-biology.com/content/article/abstract?uid=PIIS0960982206000649
>I'll post when I have more info on obtaining the full paper.


One of the authors (John F. Fallon) sent me a copy yesterday. His email address is at the link above or contact me here

John Latter

-- 
Model of an Internal Evolutionary Mechanism:
http://members.aol.com/jorolat/index.html

Please Note: If you are reading this in a Blog then replying directly to this message (as opposed to making a 'blog comment') requires membership of the 'Evolution: Where Darwin meets Lamarck?' Egroup at:
http://groups.yahoo.com/group/evomech/


Add to: CiteUlike | Connotea | Del.icio.us | Digg | Furl | Newsvine | Reddit | Yahoo


Wednesday, February 22, 2006

 

[evomech] Birds that make teeth (Press Release + Summary)

Contents:

1) Birds that make teeth
(Press Release)

Gone does not necessarily mean forgotten, especially in biology. A recent finding by researchers at the University of Wisconsin, Madison, and colleagues from the University of Manchester have found new evidence that the ability to form previously lost organs--in this case, teeth--can be maintained millions of years after the last known ancestor possessed them.

Birds do not have teeth. However, their ancestors did--about 70 - 80 million years ago. The evolutionary loss of teeth corresponded to the formation of the beak that is present in all living birds. Nonetheless, it has been known that if mouse tooth-forming tissue is in contact with bird jaw tissue, the bird tissue is able to follow the instructions given by the mouse tissue and participate in making teeth, and that these teeth look very much like those of mammals. However, Drs. Matthew Harris and John F. Fallon and colleagues have found that modern birds retain the ability to make teeth even without instruction from their tooth-bearing cousins.

Full text at:

http://www.eurekalert.org/pub_releases/2006-02/cp-btm021506.php


2) The Development of Archosaurian First-Generation Teeth in a Chicken Mutant

[Harris et al., Current Biology, Feb '06]

Summary:

Modern birds do not have teeth. Rather, they develop a specialized keratinized structure, called the rhamphotheca, that covers the mandible, maxillae, and premaxillae. Although recombination studies have shown that the avian epidermis can respond to tooth-inductive cues from mouse or lizard oral mesenchyme and participate in tooth formation 1; 2, attempts to initiate tooth development de novo in birds have failed. Here, we describe the formation of teeth in the talpid2 chicken mutant, including the developmental processes and early molecular changes associated with the formation of teeth. Additionally, we show recapitulation of the early events seen in talpid2 after in vivo activation of β-catenin in wild-type embryos. We compare the formation of teeth in the talpid2 mutant with that in the alligator and show the formation of decidedly archosaurian (crocodilian) first-generation teeth in an avian embryo. The formation of teeth in the mutant is coupled with alterations in the specification of the oral/aboral boundary of the jaw. We propose an epigenetic model of the developmental modification of dentition in avian evolution; in this model, changes in the relative position of a lateral signaling center over competent odontogenic mesenchyme led to loss of teeth in avians while maintaining tooth developmental potential.

Summary available at:

http://www.current-biology.com/content/article/abstract?uid=PIIS0960982206000649

I'll post when I have more info on obtaining the full paper.

John Latter

Model of an Internal Evolutionary Mechanism
http://members.aol.com/jorolat/index.html

(Evolution)

technorati tags: , , , , , , , , , , , , , , , , , , , , , , , , ,

Please Note: If you are reading this in a Blog then replying directly to this message (as opposed to making a 'blog comment') requires membership of the 'Evolution: Where Darwin meets Lamarck?' Egroup at:
http://groups.yahoo.com/group/evomech/


Add to: CiteUlike | Connotea | Del.icio.us | Digg | Furl | Newsvine | Reddit | Yahoo


Tuesday, February 21, 2006

 

[evomech] Genetic analysis of cavefish reveals molecular convergence in the evolution of albinism

Genetic analysis of cavefish reveals molecular convergence in the evolution of albinism
[Jeffery et al., Nature Genetics, Dec '05]

Letter:

The genetic basis of vertebrate morphological evolution has traditionally been very difficult to examine in naturally occurring populations. Here we describe the generation of a genome-wide linkage map to allow quantitative trait analysis of evolutionarily derived morphologies in the Mexican cave tetra, a species that has, in a series of independent caves, repeatedly evolved specialized characteristics adapted to a unique and well-studied ecological environment. We focused on the trait of albinism and discovered that it is linked to Oca2, a known pigmentation gene, in two cave populations. We found different deletions in Oca2 in each population and, using a cell-based assay, showed that both cause loss of function of the corresponding protein, OCA2. Thus, the two cave populations evolved albinism independently, through similar mutational events.

Full text at:

http://www.nature.com/ng/journal/v38/n1/full/ng1700.html

PDF version:

http://www-biology.ucsd.edu/labs/hoekstra/EvoDevo%20pdfs/Tabin2005.pdf

(NB I thought I had already posted this but it didn't show up in a search of the group's archives)

John Latter
-- 
Model of an Internal Evolutionary Mechanism:
http://members.aol.com/jorolat/index.html

technorati tags: , , , , , , , , , , , , , , ,

Please Note: If you are reading this in a Blog then replying directly to this message (as opposed to making a 'blog comment') requires membership of the 'Evolution: Where Darwin meets Lamarck?' Egroup at:
http://groups.yahoo.com/group/evomech/


Add to: CiteUlike | Connotea | Del.icio.us | Digg | Furl | Newsvine | Reddit | Yahoo


Monday, February 20, 2006

 

[evomech] Research points to new theory driving evolutionary changes ('04 PR + Article)

Contents:

1) Research points to new theory driving evolutionary changes (Press Release)

DALLAS - Dec. 13, 2004 - Researchers at UT Southwestern Medical Center at Dallas have used canine DNA to identify a genetic mutation mechanism they believe is responsible for rapid evolutionary changes in the physical appearance of many species.

The findings, based on data gathered from hundreds of museum specimens of dogs and from blood samples of volunteered live dogs, offer a new explanation for the sudden, rapid rise of new species found in the fossil record. They also help explain the variability in appearance among individual members of a species, such as the length of the nose in different breeds of domestic dogs.

"We're offering an explanation for a lot of different components of evolution, one that goes against the central dogma that currently explains how certain aspects of evolution take place," said Dr. Harold "Skip" Garner.

Full article at:

http://www8.utsouthwestern.edu/utsw/cda/dept37389/files/198556.html


2) Molecular origins of rapid and continuous morphological evolution

[Garner & Fondon, PNAS, Dec '04]

Abstract:

Mutations in cis-regulatory sequences have been implicated asbeing the predominant source of variation in morphologicalevolution. We offer a hypothesis that gene-associated tandem repeat expansions and contractions are a major source of phenotypic variation in evolution. Here, we describe a comparative genomic study of repetitive elements in developmental genes of 92 breeds of dogs. We find evidence for selection for divergence at coding repeat loci in the form of both elevated purity and extensive length polymorphism among different breeds. Variations in the number of repeats in the coding regions of the Alx-4 (aristaless-like4) and Runx-2 (runt-related transcription factor 2) genes were quantitatively associated with significant differences in limb and skull morphology. We identified similar repeat length variation in the coding repeats ofRunx-2, Twist, and Dlx-2 in several other species. The high frequency and incremental effects of repeat length mutations provide molecular explanations for swift, yet topologically conservative morphological evolution.

Full text at:

http://www.pnas.org/cgi/content/full/101/52/18058

PDF version:

http://www.pnas.org/cgi/reprint/101/52/18058


John Latter

Model of an Internal Evolutionary Mechanism
http://members.aol.com/jorolat/index.html

technorati tags: , , , , , , , , , , ,

Please Note: If you are reading this in a Blog then replying directly to this message (as opposed to making a 'blog comment') requires membership of the 'Evolution: Where Darwin meets Lamarck?' Egroup at:
http://groups.yahoo.com/group/evomech/


Add to: CiteUlike | Connotea | Del.icio.us | Digg | Furl | Newsvine | Reddit | Yahoo


Sunday, February 19, 2006

 

[evomech] Unintelligent Design: A monstrous discovery suggests that viruses..

[Siebert, Discover Magazine, Mar '06]

A monstrous discovery suggests that viruses, long regarded as lowly evolutionary latecomers, may have been the precursors of all life on Earth

Extracts:

Few things on Earth are spookier than viruses. The very name virus, from the Latin word for "poisonous slime," speaks to our lowly regard for them...

...Now, with the recent discovery of a truly monstrous virus, scientists are again casting about for how best to characterize these spectral life-forms. The new virus, officially known as Mimivirus (because it mimics a bacterium), is a creature "so bizarre," as The London Telegraph described it, "and unlike anything else seen by scientists . . . that . . . it could qualify for a new domain in the tree of life." Indeed, Mimivirus is so much more genetically complex than all previously known viruses, not to mention a number of bacteria, that it seems to call for a dramatic redrawing of the tree of life...

...Viruses, long thought to be biology's hitchhikers, turn out to have been biology's formative force. This is striking news, especially at a moment when the basic facts of origins and evolution seem to have fallen under a shroud. In the discussions of intelligent design, one hears a yearning for an old-fashioned creation story, in which some singular, inchoate entity stepped in to give rise to complex life-forms - humans in particular. Now the viruses appear to present a creation story of their own: a stirring, topsy-turvy, and decidedly unintelligent design wherein life arose more by reckless accident than original intent...

...The discovery of Mimivirus lends weight to one of the more compelling theories discussed at Les Treilles. Back when the three domains of life were emerging, a large DNA virus very much like Mimi may have made its way inside a bacterium or an archaean and, rather than killing it, harmlessly persisted there. The eukaryotic cell nucleus and large, complex DNA viruses like Mimi share a compelling number of biological traits. They both replicate in the cell cytoplasm, and on doing so, each uses the same machinery within the cytoplasm to form a new membrane around itself. They both have certain enzymes for capping messenger RNA, and they both have linear chromosomes rather than the circular ones typically found in a bacterium. "If this is true," Forterre has said of the viral-nucleus hypothesis, "then we are all basically descended from viruses."...

...We have been looking for our designer in all the wrong places. It seems we owe our existence to viruses, the least of semiliving forms, and about the only thing they have in common with any sort of theological prime mover is their omnipresence and invisibility. Once again, viruses have altered the way that we view them and, by extension, ourselves. As it turns out, they are not the little breakaway shards of our biology - we are, of theirs.

Full text at:

http://www.discover.com/issues/mar-06/cover/?page=1

See also: The Animal Self (New York Times)

John Latter

Model of an Internal Evolutionary Mechanism:
http://members.aol.com/jorolat/index.html

technorati tags: , , , , , , , , , , , , , , , ,


Please Note: If you are reading this in a Blog then replying directly to this message (as opposed to making a 'blog comment') requires membership of the 'Evolution: Where Darwin meets Lamarck?' Egroup at:
http://groups.yahoo.com/group/evomech/


Add to: CiteUlike | Connotea | Del.icio.us | Digg | Furl | Newsvine | Reddit | Yahoo