Atypical acorn traits, such as multiseeded acorns, have frequently been reported in oaks (Genus: Quercus), yet there is disagreement over whether such traits are advantageous or selectively neutral. Squirrel embryo-excision behavior is one factor that has not previously been considered in discussions of these traits. Several tree squirrels are known to remove acorn embryos before caching them by notching acorns apically using their incisors. We hypothesized that atypical acorns could potentially be advantageous in environments where such embryo excision occurs. To test this, we conducted germination tests on whole acorns, squirrel-notched acorns and artificially-notched acorns for Quercus alba trees that produced either single-seeded or atypical acorns. Atypical acorns included both multiseeded acorns and acorns with non-apical embryos. Atypical acorns appear to confer a survival advantage following either squirrel or artificial notching. Trees producing such acorns had higher successful acorn germination following notching when compared to trees that produced only single-seeded acorns. For acorns that had been either notched by squirrels in the field or artificially-notched apically in the lab, only acorns from trees producing atypical acorns successfully produced shoots with plumules. These acorns were planted and developed into healthy single seedlings. We review the literature for reports of atypical acorn traits, specifically multiseeded acorns, and find that this trait has been reported for 14 species of oaks, across both oak subgenera in temperate and tropical regions. We argue that atypical acorns are advantageous for oaks, allowing escape from both insect and mammalian seed predators.
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Vol. 154 • No. 2