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Plant Focus

Quercus peninsularis
A Red Oak (Section Lobatae) endemic to inland ranges of northern Baja California, Mexico

Landscape and Conservation Genetics of the Island Oak, Quercus tomentella

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Mary V. Ashley, Janet R. Backs, and Saji T. Abraham

Published May 2016 International Oaks No. 27: 83–90


The island oak, Quercus tomentella Englem., is a rare island endemic, found only on five California Channel Islands and Guadalupe Island, Mexico. Quercus tomentella is a member of Section Protobalanus that until recently had uncertain evolutionary origins and affinities. The most widespread species of Protobalanus, Q. chrysolepis Liebmann, is found on the mainland but also on some of the islands and may hybridize with Q. tomentella. Here we present the first population genetic survey of Q. tomentella using DNA microsatellites analysis. A total of 378 trees were sampled from several sites on each of the islands where Q. tomentella occurs to assess levels of genetic diversity and to determine how that diversity is partitioned within and among islands. Genotypes were also used to quantify the extent of clonal versus sexual reproduction in Q. tomentella. Cryptic clonal growth was extensive at some sites. We found that Q. tomentella maintains moderate levels of genetic diversity despite having small, isolated populations. Populations on each island are genetically distinct, and significant population differentiation also occurs within islands. Such strong local population structure is in contrast to other studies of oaks, where high gene flow through pollen generally keeps populations homogeneous over large areas.


microsatellites, California Islands, conservation genetics, clonal reproduction, island endemic, population structure, Protobalanus


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