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Clonality, fine scale genetic diversity and genetic structure in natural populations of Chamaecyparis nootkatensis revealed by microsatellite markers Berube, Yanik Jonathan

Abstract

Layering, a form of clonal propagation, has been documented to occur in Chamaecyperis nootkatensis (D. Don) Spach (Cupressaceae), but little is known about the frequency and spatial extent of this phenomenon. Clonal reproduction has the potential to greatly affect population genetics parameters such as fine scale genetic variation and genetic structure, and, ultimately, how populations evolve. C. nootkatensis is an economically important coniferous tree species in the forests of the Pacific Northwest. Five microsatellite loci were developed from an enriched genomic library of C. nootkatensis. The developed microsatellite loci showed significant inbreeding in the three natural populations of C. nootkatensis surveyed. A segregation analysis and a test for deviations from Hardy Weinberg equilibrium revealed that one of the five loci was affected by null alleles in high frequency. Interspecific amplifications showed support for a close relationship of C. nootkatensis with members of the genera Cupressus and Juniperus. These microsatellite markers were utilized to infer the frequency and spatial extent of clonally derived individuals in three natural populations of C. nootkatensis and investigate the potential effects of clonal reproduction on fine scale genetic diversity and genetic structure in this species. Clonal extent was found to vary greatly between populations and no clear relationship between clonal extent and specific habitats was detected. Clonal diversity showed that on average -23% of the trees sampled were clonally derived. Fine scale genetic structure, as detected by genetic spatial autocorrelation, and the coefficient of inbreeding increased with clonal extent. The greatest effect of clonality on fine scale genetic structure was detected between trees separated by approximately five meters or less (the average size of clonal patches). Surprisingly, no relationship was observed between clonal extent and genetic variation. Clonality may play a crucial role by propagating this species, when the effect of purging genetic load in the inbred C. nootkatensis results in extremely low sexual recruitment. Clonality may also be conserving very fit gene combinations from recombination. Key Words: Chamaecyparis nootkatensis, clonality, Cupressaceae, genetic diversity, genetic structure, microsatellite, population genetics, simple sequence repeat (SSR), yellow cedar.

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