Unravelling the evolutionary history of Eucalyptus cordata (Myrtaceae) using molecular markers
Harrison, PA and Jones, RC and Vaillancourt, RE and Wiltshire, RJE and Potts, BM, Unravelling the evolutionary history of Eucalyptus cordata (Myrtaceae) using molecular markers, Australian Journal of Botany, 62, (2) pp. 114-131. ISSN 0067-1924 (2014) [Refereed Article]
We studied the evolutionary processes shaping the genetic diversity in the naturally fragmented Eucalyptus cordata, a rare homoblastic tree endemic to the island of Tasmania. A genome-wide scan showed that E. cordata and the endangered heteroblastic E. morrisbyi were closely related, suggesting a neotenous origin of E. cordata from an endemic heteroblastic ancestor. Bayesian cluster analysis based on nuclear microsatellites assayed in 567 E. cordata and E. morrisbyi individuals revealed five genetic clusters. Two clusters comprised populations that correspond to putative ancestral gene pools linking E. cordata and E. morrisbyi. Another cluster included populations that transgressed the drowned Derwent River valley, suggestive of a wider glacial distribution. However, the majority of individuals occurred in the two genetic clusters distributed in the south-west and north-east of the range of E. cordata. The elevated genetic diversity in populations comprising these clusters suggests that they represent two recently fragmented cores of the distribution. Genetic evidence suggests that the newly described, localised E. cordata subspecies quadrangulosa has been recently selected from within the morphologically diverse, south-western cluster. We argue that multiple phases of isolation and drift have led to the contemporary pattern of molecular variation and the scattering of relictual and more recently derived populations across the species distribution.