Friday, June 6, 2008

Fitness of symbiont strategists

Since SpringerLink is having technical difficulties, I have not yet been able to read a paper that directly corrects Dean's, so I kept myself busy with this paper instead: Evolution of Marine Symbiosis--A Simple Cost-Benefit Model written by Jonathan Roughgarden and published in Ecology in 1975. 

Roughgarden took a completely different approach to modeling an example of symbiosis; he studied the fitness of the organisms by using the following parameters:
  • Wss: fitness of an individual who has not yet attempted to colonize a host and is surviving as a free-living individual
  • P: probability that an individual of symbiont phenotype successfully finds a host
  • L: probability that the host survives while the symbiont is associated with it
  • Wa: fitness of the symbiotic individual who has successfully found a host and is associated with it
  • Wsg: fitness of the symbiotic individual who has failed to find a host or whose host has died
He then assumed that the search for a host involves some cost such as "passing up suitable sites for a solitary dwelling, devoting energy for the search which would otherwise be used in nest construction, and increased exposure to predation hazard." He determined relationships between the fitness of an individual and the cost of finding a host and decided that the expected fitness of a symbiont strategist (or potentially clownfish) was PLW+ (1-PL)Wsg

Roughgarden pointed out that for symbiosis to evolve, three factors must occur:
  1. the host should be easy to find
  2. the host should survive well with the symbiont
  3. the host should provide substantial benefit to the symbiont
At this point, it seems as though there are many very different approaches I could take to modeling the relationship between clownfish and anemones, and it will be interesting to see how I end up utilizing and possibly combining some of the models I have encountered.

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