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Plasticity and evolution in drought avoidance and escape in the annual plant Brassica rapa

Department of Biology, Fordham University, 160 Larkin Hall, 441 E. Fordham Road, Bronx, NY 10458, USA.
New Phytologist (Impact Factor: 6.55). 04/2011; 190(1). DOI: 10.1111/j.1469-8137.2010.03603.x
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ABSTRACT • A key question in ecological genetics is to what extent do plants adapt to changes in climatic conditions, such as drought, through plasticity or evolution. • To address this question, seeds of 140 maternal families of Brassica rapa were generated from collections made before (1997) and after (2004) a natural drought. These seeds were planted in the glasshouse and grown under low-water and high-water conditions. • Post-drought lines flowered earlier than pre-drought lines, showing an evolutionary shift to earlier flowering. There was significant genetic variation and genotype by environment (G × E) interactions in flowering time, indicating genetic variation in plasticity in this trait. Plants that flowered earlier had fewer leaf nodes and lower instantaneous (A/g) and integrated (δ(13) C) water use efficiency than late-flowering plants. • These results suggest that B. rapa plants escape drought through early flowering rather than avoid drought through increased water use efficiency. The mechanism of this response appears to be high transpiration and inefficient water use, leading to rapid development. These findings demonstrate a trade-off between drought avoidance and escape, and indicate that, in this system, where drought acts to shorten the growing season, selection for drought escape through earlier flowering is more important than phenotypic plasticity.

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    • "Smaller and thicker leaves could be an adaptation to reduce water loss during warm and dry spells (Scheepens et al., 2010b) at the continental sites. Early flowering could be an adaptation to avoid heat or drought periods (Latta and Gardner, 2009; Franks, 2011), which may be exacerbated by the dark rock faces or screes in S. sponhemica habitats that strongly absorb solar radiation. The earlier timing of reproduction and the harsher climate may have led to the observed lower reproduction and reduced petal size (Obeso, 2002) at the more "
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    • "Consistent with drought escape, water-limited conditions often favor earlier flowering (e.g., Bennington and McGraw 1995; Heschel and Riginos 2005; Franks et al. 2007; Franks 2011; Ivey and Carr 2012; but see Sherrard and Maherali 2006). Plant species and populations often show genetically based phenotypic differentiation consistent with patterns of differential selection and/or predictions of climatic adaptation (e.g., Dudley 1996a,b; McKay et al. 2001; Heschel et al. 2002; Franks et al. 2007; Lowry et al. 2008; Wu et al. 2010; Franks 2011). Additionally, WUE and flowering time are often positively correlated (e.g., McKay et al. 2003; Sherrard and Maherali 2006); however, this is not always the case (Ivey and Carr 2012) and may depend on the scale of comparison (Wu et al. 2010) or developmental stage (Sherrard and Maherali 2006). "
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    • "Research of drought (Ludlow, 1989; McKay et al., 2003; Franks, 2011). Further, plants adapted to drier habitats typically have larger seeds than those adapted to wetter habitats, which reflects a trade-off between offspring provisioning and total reproductive output (Baker, 1972). "
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