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: 7.67). 04/2011; 190(1). DOI: 10.1111/j.1469-8137.2010.03603.x
Source: PubMed


• 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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Available from: Steven Joseph Franks, Mar 17, 2014
    • "Disproportionately large flowers therefore might further raise water costs. Under drought, plants produce smaller flowers and smaller reproductive structures in general (Mal and Lovett-Doust 2005; Caruso 2006), and were also found to advance flowering phenology as a plastic as well as an evolutionary response (Dunne et al. 2003; Franks 2011). Precipitation is very variable across the European Alps as a result of the interplay of climatic patterns with the obstructing effect of mountain ranges. "
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    ABSTRACT: The timing of and relative investment in reproductive events are crucial fitness determinants for alpine plants, which have limited opportunities for reproduction in the cold and short growing seasons at high elevations. We use the alpine Anthyllis vulneraria to study whether flowering phenology and reproductive allocation have been under diversifying selection, and to assess genetic diversity and plastic responses to drought in these traits. Open-pollinated maternal families from three populations in each of two regions from the Swiss Alps with contrasting precipitation were grown in low and high soil moisture in a common garden. We measured onset, peak, and end of flowering, as well as vegetative and reproductive aboveground biomass. Population differentiation for each character (QST) was compared to differentiation at neutral microsatellite loci (FST) to test for past selection. We found population differentiation in onset and peak of flowering which results from natural selection according to QST–FST. End of flowering and biomass were not significantly differentiated among populations. Reduced soil moisture had no consistent effect on mean onset of flowering, and advanced peak and end of flowering by less than 1 week. Reproductive biomass was strongly decreased by lowered soil moisture. No genetic variation within or among populations was found for plasticity in any trait measured. The results suggest past heterogeneous selection on onset and peak of flowering in alpine Anthyllis vulneraria and potentially indicate local adaptation to differences in snowmelt date over distances <5 km. Limited variation in plastic responses to reduced soil moisture suggests that soil moisture might not vary between populations.
    Alpine Botany 09/2015; 125(2):113-124. DOI:10.1007/s00035-015-0157-z · 1.46 Impact Factor
    • "plant and organ growth rate and phenology (Eckhart et al. 2004). For some annual species, arid environments favor early maturity as a drought escape mechanism (e.g., Donovan et al. 2007; Franks 2011). In our system, the subspecies in the more arid part of the range (parviflora) flowers earlier and has shorter flower development time, as might be expected, yet the subspecies in the wetter portion of the range (xantiana) tends to exhibit faster rates of leaf growth (Eckhart et al. 2004). "
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    Evolution 08/2015; 69(9). DOI:10.1111/evo.12745 · 4.61 Impact Factor
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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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