Abstract
Serpentine soil, which is naturally high in heavy metal content and has low calcium to magnesium ratios, comprises a difficult environment for most plants. An impressive number of species are endemic to serpentine, and a wide range of non-endemic plant taxa have been shown to be locally adapted to these soils. Locating genomic polymorphisms which are differentiated between serpentine and non-serpentine populations would provide candidate loci for serpentine adaptation. We have used the Arabidopsis thaliana tiling array, which has 2.85 million probes throughout the genome, to measure genetic differentiation between populations of Arabidopsis lyrata growing on granitic soils and those growing on serpentinic soils. The significant overrepresentation of genes involved in ion transport and other functions provides a starting point for investigating the molecular basis of adaptation to soil ion content, water retention, and other ecologically and economically important variables. One gene in particular, calcium-exchanger 7, appears to be an excellent candidate gene for adaptation to low Ca∶Mg ratio in A. lyrata.
Highlights
Serpentine soil mosaics are a classic context for ecological adaptation [1,2]
These widespread soils occur in small patches along fault lines where igneous rocks such as serpentinite are exposed. This environment is characterized by a suite of challenging abiotic factors such as low calcium-to-magnesium ratios, increased heavy metal concentrations, nutrient deficiency, and low moisture retention [3], leading to sharp transitions in abiotic conditions at the boundaries of serpentine patches [4]
The ecological community is differentiated along these boundaries as well: serpentine soils support an considerable array of endemic plant species, with serpentine specialists comprising 12.5% of native California plants, despite these soils comprising only 1% of the land area in the region [5]
Summary
Serpentine soil mosaics are a classic context for ecological adaptation [1,2] These widespread soils occur in small patches along fault lines where igneous rocks such as serpentinite are exposed. Though information regarding local adaptation is lacking for A. lyrata, its proximity to the genetic model organism A. thaliana provides an opportunity to locate polymorphisms which are associated with the serpentine soil habitat. The role of these polymorphisms in serpentine adaptation, if any, can be experimentally investigated
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