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Local adaptation of the Hawaiian endemic tree (Metrosideros polymorpha) across a long elevation gradient
|Title:||Local adaptation of the Hawaiian endemic tree (Metrosideros polymorpha) across a long elevation gradient|
|Keywords:||Evolution & development|
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|Abstract:||Elevation gradients are important drivers of divergence in trees, yet little is known about the spatial scales over which divergence occurs, nor the abiotic factors that drive divergence. The endemic Hawaiian tree, ‘ōhi‘a lehua (Metrosideros polymorpha) spans a striking elevation gradient on Hawai‘i Island, from near sea level to 2,470 m, and comprises two pubescent varieties; M. polymorpha var. incana tends to be found at lower elevations, M. polymorpha var. polymorpha is limited to higher elevations, and purported hybrids occur at middle elevations. To better understand the scale and drivers of divergence in tree populations along elevation gradients, I conducted field, greenhouse, and growth-chamber experiments on open-pollinated seedlings from six populations of pubescent M. polymorpha spanning the full elevation range of this species on Hawai‘i Island. The reciprocal outplanting experiment revealed universally low survivorship at the extreme ends of the elevation gradient, suggesting these environments are the most challenging. Results of the 12-month UV-light experiment in the greenhouse revealed relatively lower survivorship under high-UV light of seedlings from the three highest-elevation populations (counter to expectations), contrasting relationships between anthocyanin concentration and survivorship between the two varieties, and possible heat sensitivity of high-elevation seedlings. Lastly, short-term stress response tests were done under extreme environmental conditions (i.e., high UV radiation and low temperature) in a growth chamber. No seedlings from the highest-elevation population died after exposure to -5°C for four nights, while seedlings from all other populations had lower survivorship. These results indicate local adaptation at both the variety level and suggest that both UV radiation and temperature are important drivers of local adaptation of trees across long elevation gradients.|
|Appears in Collections:||Tropical Conservation Biology and Environmental Science|
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