Dr. Halos [31 August] raises many good points, I can address some of the issues, perhaps others can fill in where I leave off.
Dr. Halos states that the criteria we suggested should apply to introduction of new species. I agree with that statement. Introduction of transgenics is similar to introducing a new species. We all recognize the damage that has been caused in nearly every country by the introduction of new species. Exotics disrupt natural habitats and displace local species from their niches.
Basically, I agree that introduction of domesticated fish in native ecosystems is not good and should be avoided if possible, but for different reasons. Release of domesticated strains causes ecological problems by the sheer numbers that are released. Domesticated fish can swamp the local gene pool with genes that are poorly fit to natural conditions and, in turn, cause extinction of the native species (as with the catfish Dr. Halos mentions). If one tested domesticated fish (or transgenic fish) with our models and found no risk, this does not imply there is no risk if the fish are introduced in such numbers as to swamp the local gene pool or break up coadapted gene complexes. The risk that we are talking about with our model is due to introduction of a small number of escaped fish and the probability that they will self propagate and take over or eliminate the natural population due to natural selection, not stochastic events caused by finite population sizes.
Dr. Halos raises an interesting question regarding genetic diversity. If a domesticated population displaces a native population, what is lost ? Is it just alleles and allelic frequencies ? I think it is much more than that. There are unique co-adapted gene complexes (epistatic effects) that took millions of generations to develop. With epistasis, the whole is greater than the sum of the parts. Once these complexes are disrupted, it is difficult or impossible to reestablish.
However, the extension to call a transgene another allele and that by adding the allele we are simply adding diversity is like saying introducing an exotic species is good for the local ecosystem because it adds diversity. Remember, in the short term, exotics may add diversity but in the long term they decrease it by eliminating competitors. There is a similar analogy to transgenic fish. A transgenic animal can retain all the benefits of the native species while at the same time the enhancements of the transgene. As such, they can invade new habitats, spawn at different times, prey on animals that are not normally their food, and not be preyed on by their normal predators. In short, a transgene is not simply a new allele, it is a megamutation. Such megamutations are often the cause for the evolution of new species. This gets into Sewall Wright's shifting balance theory of evolution which would take more space than I have to explain. I guess one could argue that evolution is good, and hence megamutations are good, but then we are speaking in evolutionary time, where millions of years is a flash in time. Given such time, it would be possible to reestablish new niches etc. necessary to reestablish balance. But, I think we need to restrict our time horizon to the present and near future.
Professor of Genetics
Department of Animal Sciences
W. Lafayette, IN 47907-1151, USA
E-mail [email protected]
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