Preadaptations

[Techne]

Preadaptations (aka exaptations) are features that perform a function but was not produced by natural selection for its current use. The word "preadaptation" was co-opted () into "exaptation", however Daniel Dennett denies exaptation differs from preadaptation. A simple example of a preadaptation is a feather that evolved (through natural selection) for warmth and was coopted into a new function, flight.

 

The genomes of various ancient organisms have been sequenced and it is interesting to view the presence of several preadaptations in the genomes of these creatures. The purpose of this thread is to highlight several of these interesting findings. If anyone come across any interesting findings, post it here .

 

Various trees of life exist. For example:

1

2

3

4

5

6

7

 

For the purpose of this thread, tree #2 (Dhushara, trevol.jpg) will be used as it is a nice representation of the evolution of animals (especially vertebrates). Horizontal gene transfer and endosymbiotic events are however not clear and tree #7 (Doolittle) is probably a better way of looking at evolution. Therefore keep #2 and #7 in mind and try and piece them together.

 

Preadaptations in the genome of the choanoflagellate, Monosiga brevicollis:

Choanoflagellates (link) are single-celled organisms thought to be most closely related to animals. The divergence time of this organism was about >600 million years ago (Link) (Blue circle in image).

 

Tyrosine Kinases are crucial for multicellular life to exist and play pivotal roles in diverse cellular activities including growth, differentiation, metabolism, adhesion, motility, death (link). More than 90 Protein Tyrosine Kinases (PTKs) have been found in the human genome. Interestingly Monosiga brevicollis has a tyrosine kinase signaling network more elaborate and diverse than found in any known metazoan.

 

Adherens junctions are also crucial components of multicellular life and function to communicate and adhere together in tissues. Even though Monosiga brevicollis are single-celled and do not form colonial assemblages, it is interesting to know they posses about 23 cadherins genes (Cadherins) usually associated with multicellular organisms.

 

Calcium signaling toolkits also play a crucial role in multicellular signaling. Calcium signaling plays a crucial part in contraction, metabolism, secretion, neuronal excitability, cell death, differentiation and proliferation. Thus, it is also interesting to note that Monosiga brevicollis has an extensive calcium signaling toolkit and emerged before the evolution of multicellular animals.

 

Tyrosine kinases, calcium signaling, and adherens junctions all play a part in neural signaling and other multecellular systems. Monosiga brevicollis does not have a nervous system. Thus it is also interesting to find the presence of the hedgehog gene in the genome of Monosiga brevicollis. Signaling by Sonic hedgehog (Shh) controls important

developmental processes, including neural stem cell proliferation. (Link).

Nice article:

Multigene Phylogeny of Choanozoa and the Origin of Animals

Compare the hedgehog gene of Monosiga brevicollis to that of humans.

 

Another interesting fact about the genome of the Monosiga brevicollis is noted in this article.

Interestingly, the choanoflagellate has nearly as many introns - non-coding regions once referred to as "junk" DNA - in its genes as humans do in their genes, and often in the same spots. Introns have to be snipped out before a gene can be used as a blueprint for a protein and have been associated mostly with higher organisms.

 

The choanoflagellate genome, like the genomes of many seemingly simple organisms sequenced in recent years, shows a surprising degree of complexity, King said. Many genes involved in the central nervous system of higher organisms, for example, have been found in simple organisms that lack a centralized nervous system.

 

Likewise, choanoflagellates have five immunoglobulin domains, though they have no immune system; collagen, integrin and cadherin domains, though they have no skeleton or matrix binding cells together; and proteins called tyrosine kinases that are a key part of signaling between cells, even though Monosiga is not known to communicate, or at least does not form colonies.

 

Fascinating multicellular preadaptations very early on in the evolution of single-celled organisms.

 

Next a look at sponges.

Edited September 30, 2008 by Techne

[pioneer]

One way to look at this is evolution, in part, has a goal in mind, since preparations are being made to create the precursors for what will eventually be used for natural selection. Let me give a hypothetical example. We have a herd of deer living in good times with nice weather. Part of the herd suddenly develops this thick coat and part of the herd retains a thin coat. During good times, the thin coat deer have the selective advantage due to body cooling. Next year, the weather changes and it gets very cold, now selective advantage switches, without any change in genetics. The genetics that pre-adapted to the future may be useless for the present but was useful for the future.

 

As a human analogy, if we had two equivalent people, one stores money for retirement and the other lives in the present. During the younger years, the one living in the now will have selective advantage since they can afford the boat. But 40 years later in the future, this switches with the one with the retirement fund now having the selective advantage. We assume all else equal except this singular behavior. Relative to their offspring, the one living in the now might have an advantage relative to their children, being able to provide them more stuff. The one who saved for retirement may skip a generation but may be able to do the same for their grandchildren. This slight change of adaptation is not geared to the present but future.

 

Relative to evolution, life needs a template material like DNA or RNA, that can replicate to work. This might be replaced by other types of templates but the future of life required a template that can replicate, even before it got started. It was the anticipated step for a bunch of random chemicals even before it got started. If this goal was all random than replicators would not be needed for life and we should be able to think up endless ways to do make life without it. Even in the lab we have this goal in mind and expect that life has to follow this milestone.

[iNow]

One way to look at this is evolution, in part, has a goal in mind...

 

You've been told at least three times by me directly and several times by numerous others that this IS NOT TRUE. Simply repeating it adds no validity to your assertion, pioneer.

 

I plead with you to never again post on the subject of evolution. You truly don't get it, despite all of our best efforts to help you improve your understanding.

 

 

</me> Notes to self that Pioneer won't heed the request, will continue spouting inaccurate nonsense, and will never once supply references in support of his posts.

[Techne]

Hi pioneer,

 

Perhaps these "illusions" of foresight and preadaptations are due to our biomolecular machines ?

 

More preadaptations:

Sponges (wiki):

Sponges are among the simplest animals. They lack gastrulated embryos, extracellular digestive cavities, nerves, muscles, tissues, and obvious sensory structures, features possessed by all other animals.

Nice site about sponges,

Evolutionary history of sponges (Sponges = light blue, Divergence time = yellow)

 

Choanoflagellates had a lot of the toolkits necessary to develop a nervous system as well as multi-cellularity, even though they are simple uni-cellular organisms that do not form colonial assemblages.

 

Now the Origin of Nerves are Traced to Sponges

Sponges are very primitive animals. They don't have nerves cells (nor muscles nor eyes nor a lot of other things we commonly associate with animals). So scientists figured sponges split from the tree of life before nerves evolved.

A new study has surprised researchers, however.

 

"We are pretty confident it was after the sponges split from trunk of the tree of life and sponges went one way and animals developed from the other, that nerves started to form," said Bernie Degnan of the University of Queensland. "What we found in sponges though were the building blocks for nerves, something we never expected to find."

 

In humans and other animals, nerves deliver messages to and from the brain and all the parts of a body.

 

Degnan and colleagues studied a sea sponge called Amphimedon queenslandica. "What we have done is try to find the molecular building blocks of nerves, or what may be called the nerve's ancestor the proto-neuron," Degnan said. They found sets of these genes in sponges.

Awesome .

Free, online peer-reviewed article:

A Post-Synaptic Scaffold at the Origin of the Animal Kingdom

 

There are even more fascinating findings from the genome of the sponge.

"But what was really cool," he said, "is we took some of these genes and expressed them in frogs and flies and the sponge gene became functional — the sponge gene directed the formation of nerves in these more complex animals.

 

The research, announced this month, was published in the journal Current Biology.

 

Article with the details:

Article abstract:

Sponge Genes Provide New Insight into the Evolutionary Origin of the Neurogenic Circuit

The nerve cell is a eumetazoan (cnidarians and bilaterians) synapomorphy [1]; this cell type is absent in sponges, a more ancient phyletic lineage. Here, we demonstrate that despite lacking neurons, the sponge Amphimedon queenslandica expresses the Notch-Delta signaling system and a proneural basic helix loop helix (bHLH) gene in a manner that resembles the conserved molecular mechanisms of primary neurogenesis in bilaterians. During Amphimedon development, a field of subepithelial cells expresses the Notch receptor, its ligand Delta, and a sponge bHLH gene, AmqbHLH1. Cells that migrate out of this field express AmqDelta1 and give rise to putative sensory cells that populate the larval epithelium. Phylogenetic analysis suggests that AmqbHLH1 is descendent from a single ancestral bHLH gene that later duplicated to produce the atonal/neurogenin-related bHLH gene families, which include most bilaterian proneural genes [2]. By way of functional studies in Xenopus and Drosophila, we demonstrate that AmqbHLH1 has a strong proneural activity in both species with properties displayed by both neurogenin and atonal genes. From these results, we infer that the bilaterian neurogenic circuit, comprising proneural atonal-related bHLH genes coupled with Notch-Delta signaling, was functional in the very first metazoans and was used to generate an ancient sensory cell type.

 

Whole parts of the nervous system were present in animals that do not have a nervous system, yet these parts are interchangeable and function just like they should in animals that do have a nervous system.