Ecological, genetic and metabolic variation in populations of Tilia cordata

• Main Author: Barker, Carl
• Format: Dissertation
• Language: English
• Published: Edge Hill University 2017
• Subjects: QH301 Biology

Predicting the responses of tree species to rapid environmental change requires an understanding of their ecology, reproductive strategy, population connectivity and levels of adaptive variation. This project examines these aspects for an understudied UK native tree genus Tilia L. Comparison of edaphic and physiographic variables indicated that Tilia cordata Mill. is more generalist than T. platyphyllos Scop., as well as preferring locations with higher potential incident solar radiation and greater levels of organic carbon content. Examination of fine-scale spatial genetic structure indicates that T. cordata has a mixed reproductive system with approximately half of all individuals within sampled populations being of clonal origin. The incidence of clonality was weakly negatively correlated to historic summer temperatures and positively so to the proportion of canopy trees within samples, suggesting both fertility limitations and time since disturbance affect vegetative growth in the species. Clonal reproduction is not expected to impact future outcrossing success due to the fine scale of its effects on spatial genetic structure, being much smaller than typical pollen movements associated with outcrossing. T. cordata populations exhibited weak clinal spatial genetic structure at coarser scales (tens of kilometres) across two locations, which likely reflect historic dispersal limitations across a contiguous landscape and effective pollen movement at scales less than two kilometres. Fragmentation has not yet eroded genetic variation except in the demes with the smallest size (not necessarily the most isolated), suggesting that larger fragments may ultimately suffer the same fate. Finally, low metabolic variation between UK populations of T. cordata despite contrasting environmental conditions during sampling indicates high levels of phenotypic plasticity, while variation in a functional trait and a group of unidentified metabolite concentrations suggest avenues for examining local adaptation in the future.