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Local climatic heterogeneity predicts differences in phenotypic plasticity across populations of a widely-distributed California oak species

  • Author(s): MacDonald, Brandon William Selbie
  • Advisor(s): Sork, Victoria L
  • et al.
Abstract

In variable environments, phenotypic plasticity-- the ability of a genotype to produce different phenotypes in different environments -- may play a critical role in survival of an organism. It has been proposed that populations living in more climatically variable environments may evolve greater phenotypic plasticity than populations in more stable environments, which may be particularly beneficial for sessile long-lived organisms, such as trees, which once established will live in one location for a long time. We test this hypothesis by examining leaf traits in Quercus lobata, a wide-spread California oak, which were planted into two common gardens. Common gardens were established with 6000 seedlings grown from acorns harvested from trees across the species range. We measure leaf traits that are likely to demonstrate plasticity, and are known to be associated with plant response to climate. In support of our hypothesis, we find that leaf thickness, leaf lobedness, and trichome density show clines in plasticity in their response to the environments of the two gardens that are correlated with two measures of environmental heterogeneity—temperature seasonality and precipitation seasonality. Seedlings from climates which are more seasonal in temperature and precipitation tend to display higher levels of plasticity in the common gardens. We also find geographic structure in patterns of plasticity and identify leaf lobedness as the most plastic leaf trait in the common gardens. More plastic maternal families tend to display lower levels of fitness in the common gardens suggesting a cost associated with plasticity. We conclude that there is local adaptation for plasticity in some leaf traits, and that there is a fitness cost to that plasticity outside of the native environment.

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