Contents - Faperta

436 Biotechnological Approaches for Pest Management and Ecological Sustainability
Probability of Horizontal and Vertical Gene Flow
Long-term ecological risk can be determined from the probability that an initially rare
transgene might spread into the ecosystem, resulting in vertical gene transfer as a result
of gene introgression into feral populations, invasion of new territories as a result of introduction
of an exotic species, and horizontal gene transfer mediated by microbial agents,
or a combination of these. The relative importance of each factor depends on the species,
transgene, and the method used to insert the transgene. Vertical gene transfer depends
on the species modifi ed. If feral populations are locally available, then adaptation is not a
major barrier to gene spread, as the introgression of the transgene may take place into
highly adapted native populations. Although feral populations do not exist locally for
every domesticated species, if the transgenic plant has an economic advantage, we must
assume that human intervention will transport such organisms to area(s) of the world
where native populations exist. Another mechanism is the spread of the transgene into
new territories, depending on the functionality of the transgene. The anthropogenic
introduction of any exotic organisms into natural communities is a serious ecological
concern because exotics may adversely affect the local communities, including eliminating
populations of other species. Transgenic individuals retain most of the characteristics
of their wild-type counterparts, but also possess some novel advantages. A transgene for
enhanced environmental adaptation, such as heat tolerance, would allow the species to
invade cool and warm environments, while maintaining populations in current habitats
(Tzotzos, 1995). They may reproduce at a faster rate and their populations may increase
unchecked and thus adversely affect the other species. As a consequence, transgenic
organisms might threaten the survival of wild-type conspecifi cs as well as other species
in the community. The third mechanism of spread involves horizontal gene transfer, which
occurs through viruses and transposons (Tefper, 2002). However, horizontal gene transfer
may occur at such low rates that it would not normally be an additional concern. If a
virus or transposon is used to insert the transgene, then even if the virus is disabled, it
may be possible for the transposon element to recombine with other naturally occurring
viruses and spread into new hosts.
Regardless of the mechanism of gene spread, the ultimate fate of a transgene will be
determined by the same forces that direct evolution, that is, natural selection acting on fi tness.
Thus, risk assessment can be accomplished by determining the outcome of natural
selection for increased fi tness. This conclusion assumes that the natural populations are
large enough to recover from such introductions, that is, natural selection will have time
to readjust the population to its previous state. Fitness is not simply survival, but all aspects
of the organism that result in spread of the transgene.
Risk Management
A comprehensive strategy for risk management is necessary once a plant has to be released
for small-scale experiments and commercial production (NAS, 1989; CEC, 1990a, 1990b;
UNIDO, 1991; OECD, 1992, 1993a, 1993b; Sharma et al., 2002b). The scientists concerned, the
biosafety committee, and national and international regulatory authorities should determine
whether it is acceptable to release the specifi c transgenic plants and, if needed, restrictions
to be imposed. Field containment should be in place to limit the possible environmental