jueves, julio 10, 2008

¿Búfalo o Buey?

Plasticity in the use of novel environments: Direct Internalization and Secondary isolation mechanisms.

Bufallo bull at Jackson Hole, WY, 2008

A premise of Natural Selection (NS) is that an organism can not avoid environmental pressures and, utterly succumb or succeed under nature’s phenotypic filter. As a consequence, those exaptative phenotypes that survive the filter will be conserved in evolutionary time, meanwhile others are eliminated. 

This selective operation has worked very well for centuries in the history of the relationship of humans and domesticated animals. The breeder can select the phenotypes that she/he wants, and eliminate the others. However, this operation may not apply as an historic explanation for life’s properties and diversity. 
Among several factors that may complicate the selective scenario, lets take a look at the use of novel habitats as a way for an organism to escape its elimination under selective pressures. 
Here I will review the role of phenotypic plasticity and learning, inner properties of organism, in accommodating organism ontogenetic niche for the use of novel habitats. The role of learning as a source of novelty had been largely discussed starting with Balwin’s seminal paper in 1886. Examples of plastic changes in the use of novel habitat or under habitat changes can be found in almost all the living groups. Interestingly, in some of these cases, the plastic changes not only help the organism to withstand NS, but also help to expand their niches and diversify. 
This natural drift can be originated, among other factors, by the direct internalization of novel habitat pressures on the inheritance system of the organism. For example by epigenetic processes, like DNA methylation induced by diet or stress. Other sources of internalization may include mutation induced under stress, like transposable elements activity or DNA polymerase activity among others. Under other category of internalization we can consider all kinds of symbiogenesis, described by DeBary in 1873, as the generation of “individuality by incorporation”. The use of a new host by a parasitic organism, cohabitation, or other kind of long-term living association, results in symbiogenesis: the appearance of new bodies, new organs, and new species. 
Alternatively the diversification in novel habitats can be a consequence of phenotypic canalization of the ontogenetic niche. Under this alternative, plastic changes related with the use of the novel habitat contribute to the sympatric or parapatric isolation of the organism experiencing it, and secondarily, these isolation mechanisms would affect inheritance processes. Evidences of this kid of processes can be found in many orders, many cases of these have been discussed in Nucleo Decenio.
Thus, under the pressures of a phenotypic filter like natural selection, the organism had at least some alternatives beside to be just eliminated, thanks to plasticity and the use of novel environment, leading a change in its ontogenetic niche.
The selective reductionism framework of the “Modern Synthesis” has been proven to be an incomplete picture for understanding evolution. An actualized view of evolutionary biology has to include in first place a theory of the organism, considering its properties as protagonist of its own ontogenetic and phylogenetic change. 

“..Although Charles Darwin’s theory of evolution laid the foundations of modern biology, it did not tell the whole story. Most remarkably, The Origin of Species said very little about, of all things, the origins of species. Darwin and his modern successors have shown very convincingly how inherited variations are naturally selected, but they leave unanswered how variant organisms come to be in the first place..”
Lynn Margulis, 1998.

     Cristian Villagra


Agrawal AA. (2001) Phenotypic Plasticity in the Interaction and Evolution of Species. Science, 294.

Beltman JB., P Haccou & CT Cate (2004) Learning and Colonization of New Niches, A first step towards speciation. Evolution, 58, pp. 35–46.

Donohue K. (2004) Niche construction through phenological plasticity: life history dynamics and ecological consequences. New Phytologist. Vol 166: 83-92.

Dre`s M & Mallet J (2002) Host races in plant-feeding insects and their importance in sympatric speciation. Phil. Trans. R. Soc. Lond. B. 357, 471–492.

Hegrenes S. (2001) Diet-induced phenotypic plasticity of feeding morphology in the orangespotted sunfish, Lepomis humilis. Ecology of Freshwater Fish.10: 35–42.

Jablonka E. & Lamb’ M. J. (1998) Epigenetic inheritance in evolution. J. evol. biol. 11 159-183.

Lozada-Chávez I, Janga S.Ch. & Collado-Vides J. (2006) Bacterial regulatory networks are extremely flexible in evolution. Nucleic Acids Research 2006 34(12):3434-3445.

Margulis L. (1998) Symbiotic Planet: A New Look at Evolution. Basic Books, 147pp.

Maturana-Romesin H & Mpodozis J (2000) The origin of species by means of natural drift. Rev. chil. hist. nat. v.73 n.2.

Stamps J. (2003) Behavioural processes affecting development: Tinbergen’s fourth
question comes of age. Behaviour. 66:1-13.

Trussell GC (2000) Phenotypic Clines, Plasticity, and Morphological Trade-offs in an intertidial Snail. Evolution, 54: 151–166.

11 comentarios:

Sanders dijo...

beautiful post!

Sanders dijo...

as von uexkull pointed out, more often it is the organism that selects its environment, rather than the environment selecting the organism. This is key to understanding the process of isolation

Sanders dijo...

nice bibliography!

Nucleo Decenio dijo...

si quieren algun paper avisenme que los puedo mandar

Sanders dijo...

me parece increíble qu el único blog donde se discuten estos adelantos así directo a la vena es...NUCLEODECENIO
A blog ahead of its time... wena diablete!

Anónimo dijo...

cristián, podes me mandar o

Stamps J. (2003) Behavioural processes affecting development: Tinbergen’s fourth
question comes of age. Behaviour. 66:1-13.


valeu, abração

Cristian dijo...

ya te lo mando al tiro!

Saludos desde NY!

Sanders dijo...
Este comentario ha sido eliminado por el autor.
Sanders dijo...

una salvedad que hay que hacer es que no todos los efectos fenotípicos internalizados son necesariamente adaptaciones

Cristian dijo...

Por supuesto, la idea de la internalizacion es sacar el acento adaptativo a las alteraciones que quedan en el ADN.

"Internalization of novel habitat pressures" on the inheritance system of the organism,

Estas presiones pueden ser bien literales en el caso de las alteraciones producto de estres!, no importando si estas alteraciones le confieren mayor "fitness" a los bichos o no.

Cristian dijo...

Otra cosa que es importante discurtir, es como la anteojera seleccionista ha pasado por alto el valor de la plasticidad y la conducta en la utilizacion de nuevos ambientes.

Para este fenomeno, los seleccionistas tienen el siguiente argumento mas o menos asi:

/ En vez de tener un fenotipo que sea "fit" en todos los ambientes /(seguro por lo del "tradeoff")/. la seleccion natural permite que exista diversidad fenotipica permitiendo que diferentes fenotipos sean "fit" en diferentes ambientes.../*

Esto muestra como si nos centramos en el proceso de filtro fenotipico de la SN, nos perdemos toda la diversion de COMO se origino la novedad asociada al uso de distintos ambientes, mutacion "random", tal vez no es suficente...

* (no es wbeo!, en el mismo paper de Stamps, que me pidio Gustavo, sale este argumento!)