Testing prerequisites to adaptation in Quercus agrifolia: Are leaf domatia a heritable trait?

On Quercus agrifolia Née, Fagaceae, (Coast Live Oak) trees in California, small clusters of branched trichomes on the abaxial leaf surface serve as domatia, protective structures for mites. These structures are a distinguishing characteristic of Q. agrifolia and we hypothesize may be shaped by natural selection. Here we test the first two of three prerequisites for adaptation via natural selection: (1) the trait must vary among individuals, and (2) the trait must be heritable. Trait variance across 20 trees in a natural stand was assessed by collecting 20 leaves per tree and determining the proportion of leaf vein axils with domatia. From the same trees, acorns were collected, germinated, and the proportion of leaf vein axils with domatia was recorded for 12- and 18-month-old saplings. Heritability was then assessed by comparing the resemblance between maternal trees and offspring. We find that both prerequisites are met: maternal trees exhibit substantial variation in the proportion of leaf vein axils with domatia, ranging from an average of 0–0.85 per leaf, and heritability estimates for 12- and 18-month-old saplings were 0.33 ± 0.10SD and 0.53 ± 0.10SD respectively. A follow up study is needed to assess the third prerequisite for adaptation via natural selection, that survival and reproduction of oaks varies based on the proportion of leaf vein axils with domatia. We hope future researchers will pursue this line of study.