miércoles, mayo 28, 2008

Parental Care Usurpation as a model for thinking about Developmental Systems

Parental Care usurpators exploit the social behavior of their hosts, this “modo de vida,” it is present in numerous taxa and involve the partial sequestration of the ontogenetic niche of the host species. In this commentary I will mention two cases of parental care usurpation: the avian brood parasites (e.g. cuckoos) and the ant nest usurpations (often called slave-maker ants or pirate ants).
Due to the very emergent properties involved in the evolution of these life styles; these cases are interesting models for thinking about the value of Developmental System Theory or Evolution by Means of Natural Drift as explanatory backgrounds.

Previously in this blog, we have seen comments about the relevance of the “incomplete isolation” of the multicellulars systems processes as a way to understand certain kinds of dynamic changes in the ontogenetic niche. This “epigenetic permeability”, could be suggested as a property that may help to understand why it is not always necessarily an “Internalization” (i.e incorporation of adaptative traits in the genome of the evolving species) for the development of new life styles or lineage changes in order to get an idea of the points when this “epigenetic permeability” may help to explain the establishment and conservation of these life styles, lets compare the steps of the parasite-host interactions.

In avian brood parasites, the female lays the egg in the host nest, which has been recognized by some authors as the only interaction between the parasite and host species. I would suggest to add a second step that is performed by the parasite chick: the expulsion from the nest of the host offspring (this does not always happen though). For the realization of step one of the interaction, the parasite mother had to find the appropriate host nest and the host parents have to be fooled to keep believing that the extra egg belongs to them. Some parasites species present similar egg pigmentation with their main host, but it is not clear, as far as I´ve read, that this is genetically determined and that this trait can vary inter and intraspecies. The second step is very similar to other kind of parasitic interaction where the allocation of resources is diverted to feed the growing parasite (See Sacculina barnacles post in this blog as an example).
In ant nest usurpation species, the first step involves the usurpation of the queen host throne by the parasite ant. The female searching for nest, sneaking in the nest without being detected as alien by the colony, and (as similar as the avian parasite chick) the diversion towards the reproducing parasite.
In the second step, the parasite queen offspring will search for new host colonies, raid them and kidnap host worker’s larvae. Experiments have demonstrated that when two alternative host are available for the queen and she picks one of them in the first step, the parasite sons will also choose that one for collecting more workers.

This two examples suggest to me that the Developmental System is more than the niche variables and the inheritable organism material, and cannot be reduced to the somatic and germinal part as a satisfactory explanatory background but also the construction of these parasitic life styles due to epigenetic permeability are possible thanks to crucial behavioral operations (“conducta” in Maturana’s approach) that allow the emergence of these very externalized and dependent systems.

Cristian Villagra

martes, mayo 27, 2008

Más condenas mortales en cladística

Dénme una mezquita y un altoparlante: Su ayatola de la cladística les tiene listas un par de ricas nuevas condenas a muerte, que se cumplirán sin piedad.
¿Los desdichados en esta ocasión?

1)Pegasoferae: Este clado agrupa murciélagos con perisodáctilos. Se ha justificado por medio de inserciones de trasposones en lugares específicos del genoma (Nishihara et al. 2006) y ha aparecido en algunos otros arbolitos desde entonces (Murphy et al. 2008) pero lo cierto es que hasta el momento ningún estudio formal de secuencias típicas ni de la morfología ha confirmado la existencia de Pegasoferae. Más bien, por el lado de la morfología, esto implicaría asumir que los ungulados no existen, ya que perisodáctilos serían más cercanos a quirópteros que a artiodáctilos; si miramos los datos paleontológicos, no quedaría otra, según Pegasoferae, que concluir que los murciélagos evolucionaron a partir de algo como este lindo Condylarto (ungulado basal)

Qué les parece?

La otra condena de muerte es para este arbolito muy publicado en Nature:

La historia de la evolución del veneno que vende ese paper se ve muy linda, pero nótese: la iguana les salió entremedio de un montón de escleroglossae...es una infracción flagrante de todo lo que sabemos de evolución de lagartos... de hecho la distinción más básica de los lagartos, es entre iguania y scleroglossae. Este modelo implica la reversión de varios ragsos escleroglosos (como la misma lengua queratinizada y mayor desarrollo del órgano de Jacobson).


Nishihara, H., Hasegawa, M., and Okada, N. 2006. Pegasoferae, an unexpected mammalian clade revealed by tracking ancient retroposon insertions. Proc. Natl. Acad. Sci. 103: 9929–9934

William J. Murphy, Thomas H. Pringle, Tess A. Crider, Mark S. Springer and Webb Miller 2007 Using genomic data to unravel the root of the placental mammal phylogeny Genome Res.17: 413-421

Fry BG, Vidal N, Norman JA, Vonk FJ, Scheib H, Ramjan SF, Kuruppu S, Fung K, Hedges SB, Richardson MK, Hodgson WC, Ignjatovic V, Summerhayes R, Kochva E. 2006. Early evolution of the venom system in lizards and snakes. Nature.439(7076):584-8.

jueves, mayo 22, 2008

O presente ubíquo das simbioses em esponjas

A origem simbiótica de certos tipos celulares em filos animais basais - discutida em post anteriores (aqui, acá e nos comentários aqui) - recebe um bom apoio com os dados publicados em Science sobre a ubiquidade, abundância e diversidade de simbiontes em esponjas. Alguns trechos do artigo:

"One of evolution's more ancient animals, sponges at first glance seem quite simple--little more than loose consortiums of semiautonomous cells, stuck in one place filtering food from the water column. But a closer look reveals a surprising twist. "With many species, under the microscope you see almost exclusively bacteria" among the cells, says Piel, an organic chemist at the University of Bonn in Germany"

"These genetic studies uncovered a distinctive and extensive community, identifying more than 100 species of microbes that are found in sponges but not in the surrounding water. This distribution indicates that these bugs are long-term residents rather than passersby. An individual sponge might host dozens of different species, and overall, the molecular analyses have found an impressive variety: 14 bacterial phyla, two phyla of archaea, and several types of eukaryotic microbes."

"Microbes might have colonized a sponge early in the group's evolutionary history and acquired characteristics that enabled them to live in sponges full-time, Taylor proposes. Those sponge-loving microbes could have then spread to other sponges--and other oceans. And such a scenario could explain what may be a new phylum called Poribacteria, after Porifera, Latin for "sponge." Poribacteria have been found throughout the world, albeit exclusively in sponges."

"Whatever their function, the microbes seem important enough for sponges to pass on to future generations. In the female sponge, nurse cells, which provide the "yolk" for developing eggs, also ferry blue-green algae from the sponge's outer layers to the developing oocytes located deeper in the sponge matrix. In 2005, Kayley Usher and her colleagues at the University of Western Australia in Perth even found blue-green algae in the sperm of the sponge Chondrilla australiensis. A year later, Julie Enticknap, a postdoctoral fellow in Hill's lab, was able to culture a sponge-dwelling alphaproteobacterium from the larvae of a sponge collected off the coast of Florida, another indication of possible parent-to-offspring transmission."

"But that study highlights what may be the most baffling mystery in sponge microbiology. Usually when symbionts are passed from parent to offspring, the partners undergo what is called cospeciation, and the microbes develop a unique genetic signature and become confined to that particular host. "But that doesn't happen here," says Hentschel. The bacteria in the larvae proved closely related to those cultured from unrelated sponges growing in Jamaica, Indonesia, and the Chesapeake Bay in the United States. The best explanation for the broad distribution of this bacterium--and for many other species found across the globe--she says, is that sponges acquire their resident bacteria both from their parents and from the environment."

O trabalho termina falando em "sea-based drugs"... O que fica absolutamente claro é que a incorporação de simbiontes em organismos marinhos filtradores como esponja e hidrozooários não deve ser visto como um fenômeno raro.

The Inner Lives of Sponges. Gretchen Vogel (23 May 2008) Science 320 (5879), 1028.

viernes, mayo 16, 2008

Conditions of Evolution and Adaptation in Organisms as Autopoietic Systems

Del capítulo de Gerhard Roth en el libro "Environmental Adaptation and Evolution". El artículo entero pueden bajarlo desde los archivos del grupoyahoo de decenio (Roth1982) Provecho!

jueves, mayo 08, 2008

Myxozoa: Reductio ad absurdum

Seguindo a discussão do post anteiror sobre a origem simbiótica dos cnidócitos, publico a imagem de Myxozoa retirada de Eiras et al. Reparem os cnidócitos. Repito: Incrível os meandros que pode seguir a deriva de uma estrutura. Primeiro a simbiose com protistas; depois a redução do corpo a pouco mais do que um par destes simbiontes!

Myxobolus insignis sp. n. (Myxozoa, Myxosporea, Myxobolidae), a parasite of the Amazonian teleost fish Semaprochilodus insignis (Osteichthyes, Prochilodontidae)
JC Eiras; JCO Malta; AMB Varella; GC Pavanelli
Mem. Inst. Oswaldo Cruz vol.100 no.3 Rio de Janeiro May 2005

On real birds

Creio que não é surpreende para os milhares de leitores deste blog que seres vivos ativamente se adaptem ao seu nicho modificando sua fisiologia e sua conduta. Na última edição da revista Science há um largo estudo mostrando que mudanças climáticas foram compensadas por plasticidade fenotípica em uma população de passariformes. Sim, os passarinhos não se comportaram como passarinhos preformados esperando a guilhotina da seleção natural. Mudou o clima, mudaram a fisiologia e a conduta.

Adaptive Phenotypic Plasticity in Response to Climate Change in a Wild Bird Population
Anne Charmantier,1,2 Robin H. McCleery,1 Lionel R. Cole,1 Chris Perrins,1 Loeske E. B. Kruuk,3 Ben C. Sheldon1*

Rapid climate change has been implicated as a cause of evolution in poorly adapted populations. However, phenotypic plasticity provides the potential for organisms to respond rapidly and effectively to environmental change. Using a 47-year population study of the great tit (Parus major) in the United Kingdom, we show that individual adjustment of behavior in response to the environment has enabled the population to track a rapidly changing environment very closely. Individuals were markedly invariant in their response to environmental variation, suggesting that the current response may be fixed in this population. Phenotypic plasticity can thus play a central role in tracking environmental change; understanding the limits of plasticity is an important goal for future research.

martes, mayo 06, 2008

Acoplamento Estrutural


Duas possibilidades de encontro com o meio, e vejam o que passa quando duas dinâmicas estruturais e cruzam.

via Nelson Vaz

Gustavo Ramos

sábado, mayo 03, 2008

Origen simbiótico de un tipo celular: Los cnidocystos de cnidarios

Shostak S. 1993. A symbiogenetic theory for the origins of cnidocysts in Cnidaria. Biosystems 29(1):49-58


Did cnidarian cnidocysts originate from cnidocyst-bearing protoctistans living as symbiotic partners with an epithelial placula? If an increase in the fitness of symbiotic partners was "locked in" by an evolutionary stable strategy, co-evolution and compartmentalization could have led phyletically separate, eukaryotic symbionts to fuse and undergo nuclear merger. Traits originating in the symbiotic partners would have been brought to the "synthetic" organism and reworked through evolution into the development of an integrated organism. Support for the theory of symbiogenetic origins of Cnidaria rests on traces of symbiosis detected in the relationship of cnidarian epithelium to interstitial cells (I-cells), the precursors of cnidocyst-producing cnidoblasts: (1) epithelium and I-cell are autonomous and differ in morphology, cellular dynamics, the relationship of differentiation to proliferation and the variety of cell types formed; (2) hydras and planulas can be "cured" of I-cells and their derivatives, thereby creating "epithelial" animals which lack responsiveness but retain vegetative properties. (3) The reintroduction of I-cells into "epithelial" animals which lack responsiveness but retain vegetative properties. (3) The reintroduction of I-cells into "epithelial" animals restores missing differentiated cell and organismic characteristics. Symbiogenesis as a source of metazoan species has consequences for concepts of development, from the origins of cell lines to the evolution of differentiation.

Aún no lo leo pero desde ya recuerdo el caso de que hay babosas de mar (moluscos nudibranquios) que habiéndose comido un cnidario antozoo recuperaban los cnidocystos creciéndolos en "cnidosacos" en el dorso...este hecho tan sorprendente puede hacer más sentido si consideramos que los cnidocystos de alguna forma son un linaje distinto que puede vivir tanto en el molusco como el cnidario. Digo nomás! Véase además este link

Post-Scriptum: He comenzado a leer apenas la introducción y ya me convencí. El abstract no menciona el "detalle" de la evidencia morfológica. Es contundente. Resulta que el cnidocisto ya existe en varios protoctistas por ej. dinoflagelados depredadores y myxosporidios donde se les conoce como tricocysto o cápsula polar (ver imagen a la derecha). Las semejazas entre cnidocistos, especialmente en proceso de desarrollo, son muchas a nivel de microsocpia electrónica, mecanismo de eyección (la presión hidrostática en la cápsula polar expulsa el filamento). En protoctistas myxosporideos o microsporideos puede haber división celular incompleta , compartiendo 2 o más nucleos o cápsulas polares; los cnidocystos forman "nidos" de células interconectadas (esta falta de respeto por los límites celulares también nos sugiere un posible mecanismo conducente a la eventual fusión al genoma del cnidario). Otro dato: hay dos grupos fundamentales de cnidoscystos en cnidarios, sólo un grupo en antozoarios, y ambos en medusas, que sugieren que pueden tratrase de simbiosis con dos distintos linajes de protoctistas.

Cnidocysto de Hydra formando su tubo externo. Engel et al. The EMBO Journal (2001) 20, 3063–3073