title: The Conservation of Climatically Adaptive Genetic Variation
Creators: name: Irving, Toby
Publisher: name: University of Liverpool Repository
Year: 2023

description: Anthropogenic climate change poses a significant threat to plant populations and communities because the resulting environmental changes are expected to exceed the capacity of the individuals comprising many populations to reproduce or survive. Evolutionary adaptation can provide plant populations with the capacity to alter their climate tolerance, buffering them against the adverse effects of climate change, but requires the presence of climatically-adaptive standing genetic variation. Microclimatic variation—variability in climatic conditions over fine spatial scales—represents one potential source of such genetic variation, because locally prevailing climatic conditions differ from those in the surrounding areas, and have the potential to drive selection for variant genotypes that confer fitness advantages under those specific conditions, supporting diversity at larger spatial scales. Little is known about the capacity of microclimatic variation in landscapes to support climatically adaptive genetic variation and provide a buffer against future climate change. Furthermore, the success of ecological restoration projects that create new populations and habitats from seed might depend upon the inclusion of relevant climatically adaptive variation, yet we know almost nothing regarding the impacts of seed production techniques on the maintenance of these variants within seed stocks used in restoration. In this thesis I investigate the extent to which microclimatic conditions drive selection for distinct phenotypes and genotypes that may be climatically adaptive, in the ecological model forage grass Festuca ovina. I use two different study systems to address these issues, one based on naturally-occurring microclimatic variation across a landscape, and one in which climate conditions have been experimentally manipulated for almost 30 years. Additionally, I investigate the effects of commercial seed production on genetic diversity within F. ovina, with the aim of assessing the maintenance of climatically adaptive genetic variation in ecological restoration projects. I found that microclimatic variation linked to north- and south-facing valley slopes in the Peak District (UK ) is consistently associated with a suite of plant phenotypes and genotypes that are likely to be adaptive in the distinct conditions of different microclimates. F. ovina populations from cooler/ wetter microclimates tend to prioritise vegetative growth over reproduction, potentially increasing their ability to compete in these environments, whereas those from warmer drier microclimates prioritise sexual reproduction, which may increase the capacity of populations to persist through stressful abiotic conditions. Gene loci that are carry a signature of climatically adaptive genetic differentiation had functions linked to stress tolerance, reproductive timing and disease resistance. I documented similar genomic differentiation between experimental climate treatments at the Buxton Climate Change Impacts Laboratory, and furthermore provide evidence that the evolutionary changes there are functionally equivalent to those seen in naturally occurring microclimate populations in the wider Peak District. Finally, I compared the genetic structure of a wild F. ovina source population to later generation artificial populations derived from the source for commercial seed production and ecological restoration at Emorsgate Seeds (Norfolk, UK). Here I found that there was no signal of artificial selection during the process of raising seed commercially, between the wild source population and the fourth and sixth generation of cultivated stock. The results presented here demonstrate that microclimatic heterogeneity provides an important source of naturally occurring, climatically-adaptive genetic variation, with the potential to buffer populations against the effects of climate change by enabling adaptive evolutionary responses. Furthermore, the facts that F. ovina is obligately outcrossing, long-lived and wind pollinated appears to encourage retention of genetic variation within populations, including under long term cultivation for ecological restoration. On the basis of my results, I recommend that microclimatic heterogeneity and associated climatically adaptive variation should be carefully considered in conservation projects and in projections of species’ responses to climate change. Furthermore, the existence of climatically relevant variation in plant phenotypes and genotypes suggests that seed sourcing and commercial propagation should be undertaken to capture and retain as much of this variation as possible.