TSA 2008
Evolutionary and Genetic Trade-offs in Desert Tortoise (Gopherus agassizi) Headstarting and Restoration
1 Biodiversity Futures Consulting, 5550 Redtop Pl. Corvallis, OR 97333
(rkiester@gmail.com)
Abstract
In some cases we may not be able to reintroduce tortoises that are of the same genetic composition as the population that was previously endemic. In these cases the genetic composition of populations of tortoises to be potentially released must be set to balance conflicting evolutionary pressures. In particular, there is a trade-off between the adaptedness of a population and the adaptability of the population. On the one hand, natural selection will tend to cause populations to become adapted to their local environment. On the other hand, greater genetic variability provides greater opportunity for adapting to changing environments. Recent work on the desert tortoise (Gopherus agassizi) has demonstrated genetic differentiation within the Mojave Desert and has hypothesized that these genetic differences may be adaptive. This perspective emphasizes the idea of local adaptation and argues the case that reintroduced populations should genetically match the local wild populations. It assumes that the environment in the Mojave Desert has not changed significantly during the recent evolutionary history of the tortoise. Our perspective follows from Fisher’s Fundamental Theorem of Natural Selection and assumes that the environment of the tortoise has changed in the recent past and will continue to change in the future, due both to local anthropogenic effects and to global climate change. We therefore argue that the best reintroduction strategy is to create populations with high genetic variability to provide the greatest opportunity for evolutionary response to change. At the scale of the entire Mojave Desert we do believe that the population of tortoises to be reintroduced should be descended from parents from the Mojave Desert but that constraining genetic diversity to micro-localities within the Mojave Desert may limit evolution.