Un mundo conectado brinda a los virus la ventaja

Esta es una de las conclusiones de un nuevo estudio que evaluó cómo evoluciona la virulencia en los parásitos. La investigación examinó si los parásitos evolucionan para ser más o menos agresivos dependiendo de si están más o menos cercanamente conectados a sus huéspedes o dispersos entre grupos aislados de huéspedes.
La investigación fue conducida por Geoff Wild, un matemático fundador del NSERC en la University of Western Ontario, con colegas de la University of Edinburgh. Su trabajo será publicado en en el sitio web de Nature el 27 de mayo.
«Nuestro estudio da seguimiento a algunos hallazgos recientes que sugieren que la dispersión reducida de parásitos a través de grupos dispersos de hospederos favorece la evolución de parásitos con menor virulencia – en el caso de la gripe, por ejemplo, una suave, posiblemente menos mortal, tipo de Influenza”, dijo el Dr. Wild.
Fuente: A connected world gives viruses the edge. Disponible en: http://www.eurekalert.org/pub_releases/2009-05/nsae-acw052509.php [Accedido Mayo 29, 2009]

” Some researchers had contended from this that the parasites were evolving to support the overall fitness of the group,” he added. “The argument for adaptation at the group level is that the parasites become more prudent to prevent overexploitation and hence to avoid causing the extinction of the local host population.”
However, Dr. Wild and his colleagues were not convinced that Darwinian theory – so successful in providing explanations based on the notion that adaptation maximizes individual fitness – was ready for such a major makeover.
The researchers decided to move the arguments from words to harder science. Together they developed a formal mathematical model that incorporated variable patch sizes and the host parasite population dynamics. It was then run to determine the underlying evolutionary mechanisms, the results of which were published in the Nature paper.
“The model revealed solid reasons why lowered virulence enhanced individual fitness,” said Dr. Wild.
The researchers used an “inclusive” notion of individual fitness that has been used by biologists in other situations since the 1960’s. This “inclusive” approach recognizes that an individual has a vested interest not only in its own success, but also the success of its relatives (not the group as a whole, per se).
“Basically, we replace the notion of self-interest – an idea that underlies much early evolutionary theory – with the notion of self-and-family interest,” he said. “The difference between self-and-family interest versus group interests is subtle, but important.”
“There are several reasons why lowered virulence enhances the success of genetic lineages of parasites,” he said. For one thing, he explained, it means lower host-to-host disease transmission.
“While the more virulent strain of parasite can move among hosts readily, it does so to the detriment not of the group, but rather certain members of the group (namely individuals of the same strain – its relatives),” said Dr. Wild.
“Besides settling an argument over adaptation, we now understand better the importance of dispersal to the evolution of parasites.”
“The findings also suggest that as human activity makes the world more connected, natural selection will favour more virulent and dangerous parasites.”
Dr. Wild said the modeling approach the group took makes it possible to expand virulence theory to examine a range of potentially important biological factors.