Stacy, Elizabeth , DeBoer, Nicholas , Johansen, Jennifer , Sakishima, Tomoko .
Analysis of population structure reveals dispersal limitation and significant differentiation of extreme-habitat varieties of the dominant Metrosideros polymorpha on east Hawaii Island.
The drivers of population divergence and speciation in woody plants are poorly understood. The highly variable tree, Metrosideros polymorpha, dominates Hawaii’s forests and comprises eight varieties with divergent but overlapping morphologies and ecologies. Given the high potential dispersability of Metrosideros seeds by wind, connectivity among distant populations is often assumed to be high, and expected genetic differentiation among populations low. Recent studies of cross-fertility between two of Hawaii Island’s six varieties revealed partial, late-acting reproductive barriers consistent with a model of negative epistasis that is usually attributed to reproductive isolation above the species level. The current study examined neutral genetic structuring among 14 populations of M. polymorpha, representing four varieties on east Hawaii Island to elucidate associations between genetic structure and each of variety, elevation, and distance between populations. Variation at 6-10 microsatellite loci revealed low to significant structuring among populations with geographic distance between populations more influential than elevation. Two varieties associated with extreme habitats (high elevation and stream banks) were significantly differentiated from all other varieties/populations. The two most abundant varieties, representing early- and late-successional forms at low and middle elevations, were only weakly differentiated at neutral loci. The latter finding is consistent with earlier observations of partial reproductive isolation and frequent hybridization between these varieties on aging lava flows. Findings of this study stress the power of fine-scale studies for uncovering genetic structure within variable tree species and indicate that dispersal of this abundant tree is more limited than previously reported. Lastly, significant isolation of high-elevation and stream-bank varieties may reflect differentiation by strong selection acting in habitats with restricted distributions.
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1 - University of Hawaii at Hilo , Biology and TCBES, 200 West Kawili Street, Hilo, HI, 96720, USA
2 - University of Hawaii at Hilo, TCBES, 200 West Kawili Street, Hilo, HI, 96720, USA
Presentation Type: Oral Paper:Papers for Topics
Location: 556A/Convention Center
Date: Tuesday, August 3rd, 2010
Time: 11:00 AM