Journal Article

Evolution and ecology meet molecular genetics: adaptive phenotypic plasticity in two isolated Negev desert populations of <i>Acacia raddiana</i> at either end of a rainfall gradient

David Ward, Madan K. Shrestha and Avi Golan-Goldhirsh

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 109, issue 1, pages 247-255
Published in print January 2012 | ISSN: 0305-7364
Published online October 2011 | e-ISSN: 1095-8290 | DOI: https://dx.doi.org/10.1093/aob/mcr276
Evolution and ecology meet molecular genetics: adaptive phenotypic plasticity in two isolated Negev desert populations of Acacia raddiana at either end of a rainfall gradient

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Background and Aims

The ecological, evolutionary and genetic bases of population differentiation in a variable environment are often related to the selection pressures that plants experience. We compared differences in several growth- and defence-related traits in two isolated populations of Acacia raddiana trees from sites at either end of an extreme environmental gradient in the Negev desert.

Methods

We used random amplified polymorphic DNA (RAPD) to determine the molecular differences between populations. We grew plants under two levels of water, three levels of nutrients and three levels of herbivory to test for phenotypic plasticity and adaptive phenotypic plasticity.

Key Results

The RAPD analyses showed that these populations are highly genetically differentiated. Phenotypic plasticity in various morphological traits in A. raddiana was related to patterns of population genetic differentiation between the two study sites. Although we did not test for maternal effects in these long-lived trees, significant genotype × environment (G × E) interactions in some of these traits indicated that such plasticity may be adaptive.

Conclusions

The main selection pressure in this desert environment, perhaps unsurprisingly, is water. Increased water availability resulted in greater growth in the southern population, which normally receives far less rain than the northern population. Even under the conditions that we defined as low water and/or nutrients, the performance of the seedlings from the southern population was significantly better, perhaps reflecting selection for these traits. Consistent with previous studies of this genus, there was no evidence of trade-offs between physical and chemical defences and plant growth parameters in this study. Rather, there appeared to be positive correlations between plant size and defence parameters. The great variation in several traits in both populations may result in a diverse potential for responding to selection pressures in different environments.

Keywords: Phenotypic plasticity; genotype × environment interactions; reaction norms; trade-off; anti-herbivore defence; resource availability hypothesis; local adaptation; Negev desert; Acacia raddiana; rainfall gradient

Journal Article.  6396 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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