domingo, julio 27, 2008

Phyloepigenetics IV: Lagartija y nemátodo

Herrel et al 2008. Rapid large-scale evolutionary divergence in morphology and performance associated with exploitation of a different dietary resource. Proc Natl Acad Sci U S A. Mar 25;105(12):4792-5.


"In 1971 five adult pairs of this species were moved from the small islet of Pod Kopiste (0.09 km2) to the nearby Pod Mrcaru (0.03 km2) by Nevo and coworkers (...). Although the islet of Pod Mrcaru was originally inhabited by another lacertid lizard species (Podarcis melisellensis), repeated visits (twice yearly over the past three years, beginning in 2004) show that this species has become extinct on Pod Mrcaru. Genetic mitochondrial DNA analyses indicate that the lizards currently on Pod Mrcaru are indeed P. sicula and are genetically indistinguishable from lizards from the source population"

"Differences in head size and shape also translate into significant dif ferences in bite force bet ween populations. Our data show that P. sicula lizards consume more plant material on Pod Mrcaru compared with the ancestral population on Pod Kopiste"

"This shift to a predominantly plant-based diet has resulted in the dramatic evolution of intestinal morpholog y. Morphological analysis of preserved specimens shows the presence of cecal valves (Fig. 4) in all individuals, including a hatchling (26.4-mm snout-vent length, umbilical scar present) and a very young juvenile (33.11-mm snout-vent length) examined from Pod Mrcaru."

"The fact that 1% of all currently known species of squamates have cecal valves (13, 14) illustrates the unusual nature of these structures in this population"

"Cecal valves slow down food passage and provide for fermenting chambers, allowing commensal microorganisms to convert cellulose to volatile fatt y acids (15, 16). Indeed, in the lizards f rom Pod Mrcaru, nematodes were common in the hindgut but absent from individuals f rom PodKopiste"

"Because of the larger food base available and the increase in the predict abilit y of the food source, lizard densities on Pod Mrcaru are much greater (..) lizards on Pod Mrcaru do no longer appear to defend territories. Moreover, changes in foraging style (browsing versus active pursuit of mobile prey) and social structure may also have resulted in the dramatic changes in limb proportions and maximal sprint speed previously documented for this population"

"Although the presence of cecal valves and large heads in hatchlings and juveniles suggests a genetic basis for these differences, further studies investigating the potential role of phenotypic plasticity and/or maternal effects in the divergence bet ween populations are needed"

Herrell no discute mucho qué tan relevante puede ser la simbiosis con un nemátodo. Veamos un ejemplo de anfibios

Effects of the nematode Gyrinicola batrachiensis on development, gut morphology, and fermentation in bullfrog tadpoles (Rana catesbeiana): a novel mutualism

Gregory S. Pryor *, Karen A. Bjorndal J. Exp. Zool. 303A:704-712, 2005.


We describe a novel mutualism between bullfrog tadpoles (Rana catesbeiana) and a tadpole-specific gastrointestinal nematode (Gyrinicola batrachiensis). Groups of tadpoles were inoculated with viable or nonviable nematode eggs, and development, morphology, and gut fermentation activity were compared between nematode-infected and uninfected tadpoles. Nematode infection accelerated tadpole development; the mean time to metamorphosis was 16 d shorter and the range of times to metamorphosis was narrower in nematode-infected tadpoles than in uninfected tadpoles. At metamorphosis, infected and uninfected bullfrogs did not differ in body size or condition. Colon width, wet mass of colon contents, and concentrations of most fermentation byproducts (short-chain fatty acids: SCFAs) in the hindgut were greater in infected tadpoles. Furthermore, in vitro fermentation yields for all SCFAs combined were over twice as high in infected tadpoles than in uninfected tadpoles. One explanation for accelerated development in infected tadpoles is the altered hindgut fermentation associated with the nematodes. Energetic contributions of fermentation were estimated to be 20% and 9% of the total daily energy requirement for infected and uninfected tadpoles, respectively. Infection by G. batrachiensis nematodes potentially confers major ecological and evolutionary advantages to R. catesbeiana tadpoles. The mutualism between these species broadens our understanding of the taxonomic diversity and physiological contributions of fermentative gut symbionts and suggests that nematodes inhabiting the gut regions of other ectothermic herbivores might have beneficial effects in those hosts.

Si bien algunos nemátodos son parásitos en reptiles, otros no lo son:

Oecologia. 2006 Dec;150(3):355-61. Epub 2006

O'Grady SP, Dearing MD. Isotopic insight into host-endosymbiont relationships in Liolaemid lizards

Nitrogen isotopes have been widely used to investigate trophic levels in ecological systems. Isotopic enrichment of 2-5 per thousand occurs with trophic level increases in food webs. Host-parasite relationships deviate from traditional food webs in that parasites are minimally enriched relative to their hosts. Although this host-parasite enrichment pattern has been shown in multiple systems, few studies have used isotopic relationships to examine other potential symbioses. We examined the relationship between two gut-nematodes and their lizard hosts. One species, Physaloptera retusa, is a documented parasite in the stomach, whereas the relationship of the other species, Parapharyngodon riojensis (pinworms), to the host is putatively commensalistic or mutualistic. Based on the established trophic enrichments, we predicted that, relative to host tissue, parasitic nematodes would be minimally enriched (0-1 per thousand), whereas pinworms, either as commensals or mutualists, would be significantly enriched by 2-5 per thousand. We measured the (15)N values of food, digesta, gut tissue, and nematodes of eight lizard species in the family Liolaemidae. Parasitic worms were enriched 1+/-0.2 per thousand relative to host tissue, while the average enrichment value for pinworms relative to gut tissue was 6.7+/-0.2 per thousand. The results support previous findings that isotopic fractionation in a host-parasite system is lower than traditional food webs. Additionally, the larger enrichment of pinworms relative to known parasites suggests that they are not parasitic and may be several trophic levels beyond the host.

Correlating diet and digestive tract specialization: Examples from the lizard family Liolaemidae

Shannon P. O’Gradya, Mariana Morandob, Luciano Avilab and M. Denise Dearinga
Zoology 2005, 108 : 201-210


A range of digestive tract specializations were compared among dietary categories in the family Liolaemidae to test the hypothesis that herbivores require greater gut complexity to process plant matter. Additionally, the hypothesis that herbivory favors the evolution of larger body size was tested. Lastly, the association between diet and hindgut nematodes was explored. Herbivorous liolaemids were larger relative to omnivorous and insectivorous congeners and consequently had larger guts. In addition, small intestine length of herbivorous liolaemids was disproportionately longer than that of congeners. Significant interaction effects between diet and body size among organ dimensions indicate that increases in organ size occur to a greater extent in herbivores than other diet categories. For species with plant matter in their guts, there was a significant positive correlation between the percentage of plant matter consumed and small intestine length. Herbivorous liolaemids examined in this study lacked the gross morphological specializations (cecum and colonic valves) found in herbivores in the families Iguanidae and Agamidae. A significantly greater percentage of herbivorous species had nematodes in their gut. Of the species with nematodes, over 95% of herbivores had nematodes only in the hindgut. Prevalence of nematodes in the hindgut of herbivores was 2× that of omnivores and 4× that of insectivores.

Los dichosos nemátodos se encuentran en todas las especies de reptil que tienen válvulas cecales


Todo este cambio, en sólo 34 años.... es acaso una acumulación por selección direccional de varios genes? Grano fino, o grano grueso?

Cuánto de este cambios fenotípico drástico se debe más bien al efecto inmediato de diferentes condiciones epigenéticas, como la mentada asociación con el nemátodo?

jueves, julio 24, 2008

Natural drifting is not a crime

En dos publicaciones académicas, Nespolo (2003) y Medel (2008) han citado el trabajo de Maturana y Mpodozis (1992, 2000 "El origen de las especies por medio de la deriva natural" ) como una fuente de daño a la biología evolutiva en Chile. Es una discusión de ideas, pero el tema moral-acusatorio nos lleva a la vez a una discusión sobre personas (Sorpresa! esos señores Maturana y Mpodozis). La propuesta de Nespolo y Medel es simple: sencillamente no hay lugar para la deriva natural en la ciencia (y por esto, es dañina, sobre todo si la enseñan en pregrado).

Sin embargo, la idea de esta "mala influencia" está refutada por los hechos. Somos varios los que hemos pasado por el lab de biología del conocer y que desarrollamos investigación en journals de evolución. ¿Cómo es que se llega a ese tipo de acusaciones, entonces?
Algunos se dejan confundir por las apariencias. Para catalogarlo de "no-ciencia", les basta considerar que lo de M&M es medio filosófico, que está publicado en una humilde revistilla local, y que ha sido escrita por investigadores cuyos trabajos de investigación más técnicos son predominantemente en la neurobiología de las aves (y no así en ecología evolutiva, por ejemplo). Pero nada de esto tendría que ver con el contenido de la propuesta de la "deriva natural". No requiere haberla siquiera leído. Cuidado con las brumas del chauvinismo.

La deriva no es un trabajo altamente técnico como el que pueda publicar Nespolo en Evolution. Todos tenemos un "esquema" complejo que inspira nuestra investigación, compuesto de varias ideas conectadas y el cual conviene mucho discutir y reinventar. Esto por lo general no es posible por medio de un sólo trabajo o review técnico, y muchas veces se hace en libros, publicaciones ocasionales y revistillas humildes. Es lo que se llama "inspirational writing" y hacerlo no constituye una abominable práctica anticientífica. Más bien, es una de las tradiciones más queridas de la biología evolutiva (sea del color que sea!).

Tampoco es que necesitemos de la venia académica especial de Medel o Nespolo. Las nociones evolutivas de la deriva natural (Maturana y Varela 1973, 1984, Maturana y Mpodozis 1992) no son ajenas a la discusión teórica de la biología evolutiva (Balon 2003, Roth 1982). También se cita el aporte de Maturana y Varela en temáticas tan importantes para la comprensión de la evolución como lo es la discusión sobre el rol de los genes (Neuman-Held 2000) y la auto-organización en los seres vivos (Kauffman 1996). Los escritos de Maturana y coautores han sido traducidos a distintos idiomas (incluyendo la deriva natural) y han producido discusión en varias ramas de la biología, una de las cuales es la biología evolutiva. Otra es el campo de la abiogénesis (origen de la vida; Luigi Luisi 2006, Margulis 2000).

Medel y Nespolo se concentran en la acusación central de que M&M es un repudiable trabajo no-científico. Como es un trabajo que supuestamente no vale la pena, la discusión del contenido es notablemente rudimentaria y selectiva. Sólo dan a entender dos cosas 1) lo encuentran confuso y mal escrito, que no se entiende y/o 2) no perdonan el destronamiento de la selección natural como principal mecanismo evolutivo o "fuerza" detrás de la adaptación.

Ni una palabra sobre autopoiesis, genotipo total, el campo epigénico, la noción sistémica de herencia, el nicho ontogénico...todos temas recurrentes en M&M y en este blog. No dan la menor luz de comprender el "core" de la propuesta de M&M.

Como el epicentro de la acción es la facultad de ciencias de la universidad de chile, resulta que tenemos muchos amigos en común algunos de los cuales sufren cuando corren estas discrepancias y que desean, correctamente, que seamos todos amigos. Pero tengan en cuenta que nadie les ha hecho a ellos jamás acusaciones públicas (y menos en medios académicos) de tener ideas no científicas y de dañar a la ciencia en Chile. Al acusar de estas cosas, no es como que ellos se dejen a sí mismos mucha opción que no sea el rechazo absoluto

Onde Está o organismo?

A discussão do post anterior tratava dessa metáfora informacionista da Biologia oficial, e coincidentemente agora recebi do professor Nelson Vaz esse artigo publicado hoje na revista Nature. Essa é a figura que, segunda eles, representa um organismo. Está tão preciosa que julguei merecer um post.

É muito interessante essa figura porque além de um emaranhado de fios transportando a informação e de um painel de controle central desta informação, o organismo aí é uma Caixa (não preta, mas cinza, neste desenho).

Não somos nós que estamos dizendo que esta abordagem da Biologia exclui o organismo, são eles mesmos.
abraços Gustavo

Ref: Nurse, P. Life, logic and information. Nature 454: 424-426

martes, julio 22, 2008

What is so informative about information?

What is so informative about information?
Carlos M. Hamame, Diego Cosmelli, and Francisco Aboitiz (2007) . Comentario sobre: "Précis of Evolution in Four Dimensions" Eva Jablonka and Marion J lamb
Behavioral and Brain Sciences 30: 371 – 372

Abstract: Understanding evolution beyond a gene-centered vision is a fertile ground for new questions and approaches. However, in this systemic perspective, we take issue with the necessity of the concept of information. Through the example of brain and language evolution, we propose the autonomous systems theory as a more biologically relevant framework for the evolutionary perspective offered by Jablonka & Lamb

Hablando del tremendo daño a Chile con que según Medel (2008) carga el legado de Maturana, ya mencionaba anteriormente que por aquel fatídico templo de endoctrinamiento que era el lab "el rayo" había pasado Francisco Aboitiz. Ahora, entiéndase bien: Aboitiz tiene "ADN" darwinista. Al menos donde quedamos la última vez, la cuestión era la selección natural, y le molestaba el manejo de M&M de ese tema.

En realidad, pasar por el lab de Maturana no es un lavado de cerebro. Cada cual termina recogiendo lo que le guste, aunque no esté de acuerdo con otra cosa. Por lo general, se quedan con algo. Es por eso que fue grato leer el artículo arriba citado, donde estos autores producen una elegante crítica de Jablonka y Lamb muy en sintonía con nuestra forma de pensar:

"However, while the authors dispute the gene-centered notion and consider evolution as a systemic multilayered phenomenon, we believe they fall short in one critical aspect: J&L rely heavily on the notion of “information transmission” in a rather loose manner. Their approach is liable to the argument that in order to have any such thing, one needs a transmitter, a message, and a receiver – something that is not easily found when dealing with biological phenomena"

"One influential hypothesis states that living systems are those that maintain organizational closure: they are constituted by networks of self-sustaining processes, regardless of the materials used to instantiate such loops; that is, they are autonomous systems (Maturana & Varela 1973; Varela 1979). When one understands organisms this way, the notion of information transmission becomes less appealing: a closed system cannot “have” information in itself"

El artículo de Hamame et al 2007 está en el grupoyahoo bajo el nombre "Précis of Evolution in Four Dimensions" Muy recomendado

Sobre las Malas Influencias de la Deriva Natural

“Although this doctrine stimulated an interesting debate among
Chilean naturalists it had a strong detrimental impact on several
cohorts of students, ultimately retarding the advance of
evolutionary biology research in Chile”….

Queridos Amigos,

Después de muchas batallas editoriales, por fin ha salido en papel el quinto artículo y final de mi tesis acerca del aprendizaje olfativo en la búsqueda de pareja en avispas parasitoides (en la base de datos).
Estos trabajos exploran el valor del aprendizaje en diferentes estados de la ontogenia del insecto y como estas instancias están relacionadas con la preferencia de hábitat reproductivo y la fidelidad al hospedero.
En el caso de insectos que viven con fuerte dependencia a otro organismo, como por ejemplo una planta huésped, este tipo de aprendizaje podria estar relacionado con del origen de razas especializadas a hospederos y especiación simpátrica. Esto ha comenzado a reconocerse por varios autores contemporaneos trabajando en interacción insecto-planta (ver referencias en post
¿Búfalo o Buey? por ejemplo).

Estos experimentitos fueron enriquecido por las interesantes conversaciones sobre evolución y comportamiento con Jompoma y Marín en la Chile, las discusiones sobre especiación simpatrica en insectos con el querido Profesor Frías en la UMCE, y esas agradables tardes de viernes del Decenio en el Rayo.
Tal como ha sido el caso de muchos otros investigadores jovenes de Chile y Brasil (estudiantes de esas "cohortes mal influenciadas") este trabajo fué inspirado por el marco teórico de la biología sistémico-histórica.

¡Viva la Revolution!

Cristian Villagra, PhD
Postdoctoral Associate
Dept. Neurobiology and Behavior
Cornell University, Ithaca, NY

lunes, julio 14, 2008

Fisiologia (Cardíaca) Desenvolvimental

Um dos maiores problemas da biologia pré-formacionista e adultocêntrica é o desprezo óbvio pela história. Foca-se nos genes do ovo e então se pula direto para se mirar dois adultos competindo por sexo e comida. Bom, esse hiato que nos esconde a história do organismo, um ponto cego na biologia neo-Darwinista, é justamente um dos pontos de interesse de Teorias realmente epigenéticas, como a Deriva Natural.

Curiosamente, ao ser pré-formacionista e adultocêntrica, esta biologia é também finalista. Por esta razão, mesmo no momento em que o desenvolvimento retorna a ser uma disciplina relevante para a Biologia, vemos também surgir o Bad e o Ugly (termos colocados pelo Vargas em outro post), enquanto a história continua ausente do foco no mainstream. E nesta developmental fashion week, continua-se a mirar um embrião como um adulto incompleto, como um simples trânsito para o estágio final – finalismo velado!

Lembro-me que quando o Mpodozis esteve aqui em Florianópolis ele comentou que deveríamos entender um fígado embrionário no contexto da dinâmica do embrião, e não pensando no que ele deverá estar fazendo enquanto um fígado no animal adulto. Por este motivo, me agradou muito encontrar esse artigo que fala de uma “Fisiologia cardíaca desenvolvimental” – termo criado pelo autor, que explicita sua preocupação em compreender o que faz o coração no embrião, no contexto do desenvolvimento, não como um órgão se preparando para bombear sangue no futuro! Isso é muito relevante, pois quase todas as descrições do desenvolvimento cardíaco têm esse viés de explicar a formação de um órgão para bombear sangue. É explicação baseada nas expectativas do observador, que remete ao futuro, e que desreipeita uma lógica de construção histórica.

Agora falando de fato sobre o assunto, vejam vocês, que curioso: nos períodos mais iniciais do desenvolvimento embrionário, o embrião realiza suas trocas gasosas através de uma simples difusão; até que a partir de um certo tamanho isso não é mais possível e então se observa que há ali agora uma circulação sanguínea e um coração batendo! Então isso basta para se dizer que o coração surgiu para manter a oxigenação. Mas vejam neste gráfico. Ao contrário do que se esperava desde uma perspectiva funcionalista (painel superior da figura), o coração começa a bater ANTES do embrião atingir esse tamanho que impossibilita a difusão (figura do painel inferior).

Quer dizer, nos períodos iniciais está lá o animalzinho fazendo difusão e batendo seu coração... Tira-se fora o coração aí e o que se passa? O embrião continua vivendo e oxigenando seus tecidos. O coração surge num contexto independente desta função de nutrição de oxigênio. Não surge para realizar esta função, que atribuímos ao coração no adulto. O que faz o coração aí? Para entender isso, precisamos entender seu contexto de relações e sua história, não sua finalidade (sua função), por isso a explicação funcionalista não nos serve.

Então encontrei este elegante manuscrito de Waddington (1937): “THE DEPENDENCE OF HEAD CURVATURE ON THE DEVELOPMENT OF THE HEART IN THE CHICK EMBRYO”, em que ele remove o coração do embrião para observar as conseqüências disso no resto desenvolvimento. Os principais achados dele eu reproduzo aqui:

"1. The heart was removed from chick embryos of seven to twelve somites, and the embryos cultivated in vitro. The operation abolished the normal twisting of the anterior part of the embryo on to its left side and the general bending of the brain region into an arc. These two processes therefore seem to be dependent on the normal development of the heart.

2. The embryos showed a bending of the forebrain relative to the midbrain, which is therefore independent of the development of the heart.

3. The embryonic blood system, including the aortic arches, developed normally in many cases, but the blood vessels became enormously dilated.

4. The lateral evaginations of the foregut and the visceral arch mesenchyme underwent the first stages of differentiation in atypical positions, seemingly independently of each other or of any other structures

Enfim, compartilho com vocês este raro momento em que se mira a construção de um órgão sem se preocupar com a sua finalidade, sem vê-lo como um trânsito para sua futura função.



Burggren, W., Crossley, D. A. Comparative cardiovascular development: improving the conceptual framework. Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology. Volume 132, Issue 4, August 2002, Pages 661-674.

Waddington C_1937.The dependence of head curvature on the development of the heart in the chick embryo. J Exp Biol

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.

martes, julio 08, 2008


Inverted Dobzhansky (in Chilean Andes)

This phrase was recently uttered at an evo-devo symposium by MQ Martindale. By turning Dobzhansky's dictum on its head, Martindale was referring to how the study of the development of marine invertebrates is crucial to reconstruct the evolutionary history of metazoa (1). However, this phrase can find unsuspected depths in its resonance, quite beyond the reconstruction of natural history. It reminds us of the big crime that was the elimination of developmental biology from the neodarwinian synthesis (buried in the name of population genetics).
In fact, the actual priority that should be given to organismal biology, including development, continues to evade much mainstream evolutionary biology, which continues to show too much adaptationist-reduccionist nonsense as a result of a doctrinary enthronization of population genetics.
Take the case of Richard Lewontin. He gets close to the truth on many counts but does not acknowledge the centrality of having a theory of organism. Without this, placing the focus on population genetics (his field) will always be misleading: the organism is collapsed between the gene level and the population level. In other words, to get a correct view of evolution Lewontin would have to renounce to population genetics as the basic framework and thus be willing to erase the blackboard for a new starting point. Notice that by erasing the blackboard I do not mean to destroy the achievements of population genetics, denying any of its utility for answering specific questions. It is merely not to consider it as starting point of all evolutionary understanding.
In fact, biology is a larger topic than population genetics, even larger than evolution itself. Yet the absence of a generally accepted theory of organism has led to confuse the branch with the root: thus the vaccum at the roots is not properly acknowledged.
This, however, did not happen to Humberto Maturana upon being asked by a medicine student "what happened at the origin of life, such that we can say that life began?". Suddenly realizing he did not have a theory of organism, Maturana blushed and was only capable of promising the student he would think it over and answer his question next year.
The result, as many chilean and brazilian biologists already know, was the theory of autopoiesis, a theory of the basic organization of the living. A systems perpective providing minimal theoretical terms for understanding exactly what is goig on in organisms, such that they exhibit the properties we observe. This is not a definiton made for evolutionary biology; it is a definition for life, and as such, universal to all biology. This is why the notion of auotopoiesis has proven fruitful in the theoretical discussion of fields of biology that would appear completely dispar, for instance, the study of abiogenesis; inmunology; and neurobiology (not to mention a somewhat distorted use of the term that has become very popular in the social sciences).
And it so happens that the systems perspective of autopoiesis, focused on the organism, has implications for the understanding of evolution, too...

(1): Like myself, Martindale proposes a ctenophore-like ancestor of bilateria: See Vargas and Aboitiz 2005.

lunes, julio 07, 2008

¿Qué es una adaptación?

Desde la perspectiva seleccionista, una adaptación es un rasgo que confiere una ventaja selectiva, es decir, algo que tiende a imponerse en la población. Un problema evidente de esta definición es que existen muchas adaptaciones que evidentemente no confieren ninguna ventaja competitiva, ya que estan presentes en todos los miembros de una población, por ejemplo, los ojos.

Desde una perspectiva sistémica, podría argumentarse que un rasgo adpatativo es un rasgo cuya modificación tiene el efecto de que el sistema pierde su organizacion y las propiedades que resultan de esta (generalmente, la desintegración de un ser vivo). Sacamos una parte de la máquina; si sigue funcionando, no era una adaptación, sino un rasgo neutro. Un rasgo estructural concreto, pero de ninguna relevancia sistémica inmediata.

El darwinista reclamará que esta perspectiva no incluye la reproducción: por ejemplo, si le corto un cuerno a un ciervo, puede argumentarse que éste tendrá menor "éxito reproductivo", pero no se morirá. Ya que el ciervo aún conserva su autopoiesis tras perder sus cuernos, ¿podemos afirmar que los cuernos no son una adaptación?

En este punto es interesante priorizar a la autopoiesis sobre la reproducción como condición de lo viviente. La noción sistémica de adaptación no contempla la reproducción. Hay buenos argumentos teóricos y empíricos para justificar esta exclusión. De partida, pese a tener cuernos muchos ciervos no se reproducen, y en muchos agregados sociales de organismos (partiendo por la comunidad celular que consitituyen nuestros cuerpos) se diferencian linajes que no son capaces de reproducirse: en tanto se reúnan las condiciones para que se repita un fenotipo que no se reproduce, este fenotipo se continuará repitiendo y podrá constituir un linaje.

El hacer estas distinciones no implica desconocer el hecho de que los organismos generalmente se generan por algún tipo de reproducción en vez de abiogénesis (nótese que la autoreproducción no es un requisito: puede ser aloreproducción, también). Lo que sucede es que la adaptación se constata a un nivel organísmico más básico. La constitución de un linaje es un fenómeno diferente, que requiere de la previa conservación de la adaptación. Quizás es legítimo decir que para la constitución de un linaje, la reproduccion es una condición adicional. Pero no lo es para constatar la adaptación. ¿Es esta la distinción apropiada? ¿Es necesario agregar algo más?

Nótese que según la noción sistémica, en la constitución de un nuevo linaje, la adaptación se conserva, pero no puede decirse de ninguna manera significativa que la adaptación aumenta. La noción de Fisher, de que un aumento de la adaptación es un requisito para que ocurra evolucion, no reviste ninguna utilidad científica.