Landscape genetics of Alnus glutinosa across contrasting spatial scales in a natural river system

Abstract

The genetic diversity and genetic structure of populations, and the processes shaping gene flow within and between populations, are influenced by the landscapes they occur within. Within terrestrial landscapes, rivers and their riparian habitat are among the most dynamic, diverse and complex of landscapes and their linear structure appears as an interlinking feature across large landscapes.

This thesis took a landscape genetics approach to examine the influence of river landscape features on Alnus glutinosa populations, a widespread keystone tree species of European riparian ecosystems. By accounting for the differing dispersal mechanisms of A. glutinosa (wind and water), landscape effects on seed- and pollen-mediated gene flow, genetic diversity, demographic and genetic structure were identified at different spatial scales of a large UK river catchment.

Widespread gene flow within and between A. glutinosa populations was identified with no apparent limitation of wind-mediated pollen dispersal. Hydrochorous dispersal of seed between populations was evident, and found to increase genetic connectivity between riparian populations; however an isolation by distance effect was identified between populations located further apart from each other. No pattern of genetic diversity was found, with high levels of genetic diversity identified at all spatial and temporal scales. At the river-catchment scale no genetic clustering was observed, either within or between the six rivers studied. Demographic structuring within A. glutinosa populations was evident, and correlated with distance from the main river channel. Interactions between seed dispersal, hydrological disturbance, colonisation, and historical influences are discussed in relation to fine-scale spatial genetic structure between A. glutinosa sapling and adult generations.

Central to the landscape genetics approach taken in this thesis was the incorporation of key A. glutinosa life history attributes. By incorporating gene flow analyses, species ecology and landscape features, the research presented here furthers our understanding of riverine landscape influences on their riparian populations at different spatial scales and can be used to inform management principles.