Ex situ conservation of wild plant species: time to reassess the genetic assumptions and implications of seed banks

Ex situ conservation of wild plant species through seed banking is currently being recommended as a conservation strategy to help preserve the biological and genetic diversity of wild plants. Here I argue that ex situ collections may be ineffective at preserving genetic diversity and the evolutionary potential of populations for adaptive or neutral evolution. Treating the collection of genetic variation for seed banks as simply a problem in efficient sampling of neutral, allelic genetic polymorphism is a limited view of the types and organization of genetic variation present in wild plant species. Perspectives on genetic variation from neutral alleles to quantitative variation are necessary when considering evolutionary change. Quantitative genetic variation and genetic correlations determine the degree and form of response to natural selection on polygenic traits. Population variation in the amount of quantitative genetic variation or structure of genetic correlations argues that different populations will respond differently to the action of natural selection and are therefore unique evolutionary entities. Unavoidable selection on single traits will cause indirect selection on genetically correlated traits, possibly resulting in phenotypic changes and a reduction of genetic variation. Genotype-by-environment interactions demonstrate that the success of releasing seed bank genotypes in natural populations is dependent on the likelihood that seed bank material contains genotypes of high relative fitness in introduction habitats. Such actions can cause introduction of nonadaptive genotypes that will depress population fitness. Because not all types of genetic variation are highly positively correlated, sampling methods based on the neutral theory of alleles or allelic data will not necessarily capture representative quantitative genetic variation. More research on the relationship and evolutionary significance of allelic and quantitative genetic variation in collections and wild populations is needed. Initial and ongoing data on the fate of different types of genetic variation are required to determine the relative success or failure of ex situ conservation methods and to test assumptions of current programs. In situ conservation of ecosystems may offer distinct advantages for many plant species by preserving both genetic and ecological information.