Gene dispersion processes are key mechanisms that shape the genetic structure and diversity of forest stands. Gene dispersal occurs by means of both natural migration of pollen and seed as well as via the artificial transfer of seeds and plants. These processes affect the genetic structure of forest stands and thereby influence their ability to adapt to future changes in the environment. Thus, the success of natural regeneration may be influenced through effects of gene dispersal on genetic quality and diversity. Similarly, gene dispersal via artificial transfers of populations will alter the genetic composition of stands. Oaks are particularly susceptible to the effects of gene dispersal as they have the capacity for interspecific hybridisation. This hybridisation can occur between two temperate species as well as between a temperate and a Mediterranean species providing they come into contact by gene dispersal. Although gene flow may have beneficial effects by enlarging the genetic diversity of a species it may also act detrimentally by introducing undesirable genes into autochthonous populations.
Changes in population genetics due to gene flow and hybridisation are set to increase in the near future. The 20th Century has witnessed a huge modification to the genetic composition of forests due to the intensive use of plantations. These artificial changes will be reinforced by the natural colonization of abandoned farm land by forest trees and by the northward migration of species induced by the climatic changes. Out of all the European forest tree species, the genetic composition and future adaptation of oak species are likely to be the most affected by these changes. This is not only because they occupy a large proportion of European forests, but also because oaks are highly interfertile and interspecific hybridisation is common, not only amongst temperate species (e.g. Quercus robur and Q. petraea), but also between temperate and Mediterranean species (e.g. Q. pubescens and Q. faginea). Due to the influence of global climate change, Mediterranean oak species will probably be able to colonise more northerly latitudes giving opportunities for hybridisation with local temperate species and the possibility of generating new genetic combinations. Furthermore pioneer species quite rapidly colonise abandoned farm land through natural seed dispersal, and the availability of new niches for colonization by native and alien oak species is likely to provide a dynamic forum for such hybridisation events. Indeed, hybridisation events between alien and native species, due to introductions, range changes and the availability of new niches, are responsible for a large number speciation and introgression events (Anderson, 1949 ; Abbott, 1992). And the consequences of dynamic genomic recombinations following hybridisation to plant adaptation and evolution are only just being realised (Rieseberg, 1995).
Thus the future composition of European oak forests will be faced with new challenges due to the interaction between natural dispersal processes and human introductions of non-native material. Until recently the assessment of genetic diversity in populations has usually been addressed by monitoring levels and distribution of genetic variation. However, levels of diversity are usually not modified by human interference in the short term but delayed for a few generations. In contrast, changes to regeneration regimes and other silvicultural treatments have immediate impacts on dispersal mechanisms; and as a result, such modifications to gene flow processes are expected to cause more immediate change to the distribution of genetic diversity. Rather than focusing on the changes in the distribution and levels of diversity, this project will address key biological mechanisms that may interact with human interferences to generate and modify diversity in these scenarios.
The work outlined in this proposal builds on a sound foundation of information and techniques established in previous EU-funded projects. In the past the study of gene flow has been hindered by the lack of appropriate techniques but recent advances in molecular technology have provided powerful tools which enable questions regarding gene dispersal and hybridisation to be tackled. During the course of a previous FAIR project a set of highly variable microsatellite markers were used to fingerprint 200-400 trees in each of a range of European oak woods. This work will form the base from which it will be possible conduct parentage analysis on seed and plants derived from these woods which, in turn, will enable pollen and seed movements to be traced. In addition, a geographic map of highly differentiated chloroplast DNA markers was constructed during the FAIR project which was used to indicate paths of previous natural colonisation. This map will be used to indicate examples of past artificial transfers. Furthermore, a genetic linkage map is now available which will enable the genetic consequences of hybridisation to be identified. Past achievements in the form of molecular markers, geographic and genetic maps and experimental plots will be combined in this project to detect, quantify and evaluate the consequences of gene flow and hybridisation in oak.
The project aims at three major objectives:
- To trace and quantify gene flow and hybridisation in terms of distances and rates (workpackage 1 and 2)
Effective natural pollen and seed movements will be detected in 12 stands distributed throughout Europe from Scandinavia to Spain based on parentage analysis using microsatellite markers. Gene flow will be quantified as distances and rates of dispersal and will be delivered in the form of dispersal curves. Past artificial seed transfer will be detected at a local or national level by analysing the distribution of cpDNA.
- To evaluate genetic and ecological consequences of gene flow and hybridisation on the adaptation of oak stands (workpackage 3 and 4)
Genomic modifications due to the insertion of new genomic segments will be localised on genetic linkage maps, hence genomic regions that are "sensitive" to gene flow or hybridisation will be identified. The fitness of interspecific hybrids will be compared to their parents, both in situ and ex situ (in controlled environments).
- To evaluate impacts of gene flow on management rules and silvicultural regimes of oak stands (workpackage 5)
Detection and evaluation of gene flow will lead to practical decisions and silviculture recommendations concerning the management of seed and conservation stands. Furthermore computer simulation models will forecast short term and long term consequences of gene flow on the distribution of diversity in oak stands.
End-users of the project (Forest services, Conservation agencies) will be closely associated in testing various implications of gene flow in management and conservation issues.