Genetic Variation Amongst and Within the Native Provenances of Pinus radiata D. Don in South-eastern Australia. 3. Molecular and Quantitative Structure

Patterns of differentiation between populations within a species can be examined using both molecular and quantitative data, with observed differences indicative of adaptation to local conditions. Pinus radiata D. Don (radiata pine) is a species of commercial importance in many countries but also listed as conservation dependent in its native range on the Californian coast and two off shore islands. This paper presents a comparative analysis of existing molecular data with new quantitative data from a large provenance/progeny trial in southeastern Australia. Microsatellite data was reanalysed using a Bayesian model to test whether the a priori assumption of five natural occurrences was valid. With the validity of the geographic structure confirmed, two further approaches were used to examine genetic structure 1. a comparative study of F_st and Q_st estimates to investigate the role of drift and selection in shaping the differentiation between the populations for breeding traits and 2. population clustering based on both quantitative and molecular data. Results strongly support the hypothesis that the island provenances of Pinus radiata are distinctly different to the mainland provenances. The molecular evidence also indicates the island provenances are different to each other. However, these differences were not apparent for the quantitative traits related to tree growth and form. The two island populations were however, strongly differentiated from each other for wood density and acoustic velocity. The patterns of phenotypic differentiation of the island provenances for these wood traits are both consistent with, and greater than, that observed for the molecular data, providing some evidence for directional selection on these traits. This study provides a background for the interpretation of molecular studies aimed at detecting molecular signatures of selection and associating genetic variation within genes with these traits.