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Genetic diversity, population structure, mating system and pollen flow in arbutus (arbutus menziesh pursh) Beland, Jaclyn Darlene

Abstract

Arbutus (Arbutus menziesii Pursh) is the only broadleaved evergreen tree native to Canada. It is a member of four natural plant communities in British Columbia (BC) considered to be at risk as identified by the BC Conservation Data Centre, the main contributing factors being urban encroachment, fire suppression, grazing and exotic invasive species. Very few studies have been conducted on this species, and no data is available on pollination biology or population genetics. Amplified fragment length polymorphisms (AFLPs) were used to conduct the first genetic examination of A. menziesii in BC. The study included 10 populations spread throughout the geographic range of arbutus in BC as well as one population from Washington State. Genetic diversity estimates were low (mean H within populations = 0.094) relative to long-lived perennials on average (0.25); there were no significant differences among populations. Significant partitioning of genetic variation among populations was detected (FST = 0.15, ΦST = 0.16). This estimate was comparable to the average in long-lived perennials and frugivores-dispersed species (FST = 0.19 and 0.16, respectively). Jackknifed estimates of FST , a dendrogram of Reynolds' coancestry coefficient for all populations and a principal components analysis all suggested that the Gold River, BC population seemed to differ more from other populations, although this trend was not statistically significant. Isolation by distance was significant based on kinship coefficients (p < 0.01): half-sibs were approximately three metres apart. Mating system analysis of the Amelia Island, BC population revealed a high outcrossing rate (0.97), although 10-20% of mating events were attributed to biparental inbreeding. Pollen flow in this population was also investigated using a paternity analysis. Due to the low genetic variability detected in this species as well as the significant biparental inbreeding, the ability to confidently assign paternity was limited. Comparison of paternity assignment at LOD score threshold values of 4 and 5 revealed the characteristic leptokurtic distribution of pollen in many other plant species. The information generated from this investigation is discussed with respect to conservation strategies, and future directions in the study of the genetics of arbutus are suggested.

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