Multiple modes of convergent adaptation in the spread of glyphosate-resistant Amaranthus tuberculatus
0301 basic medicine
2. Zero hunger
0303 health sciences
03 medical and health sciences
Biological Sciences
15. Life on land
DOI:
10.1073/pnas.1900870116
Publication Date:
2019-10-01T02:31:38Z
AUTHORS (12)
ABSTRACT
The selection pressure exerted by herbicides has led to the repeated evolution of herbicide resistance in weeds. The evolution of herbicide resistance on contemporary timescales in turn provides an outstanding opportunity to investigate key questions about the genetics of adaptation, in particular the relative importance of adaptation from new mutations, standing genetic variation, or geographic spread of adaptive alleles through gene flow. Glyphosate-resistant
Amaranthus tuberculatus
poses one of the most significant threats to crop yields in the Midwestern United States, with both agricultural populations and herbicide resistance only recently emerging in Canada. To understand the evolutionary mechanisms driving the spread of resistance, we sequenced and assembled the
A. tuberculatus
genome and investigated the origins and population genomics of 163 resequenced glyphosate-resistant and susceptible individuals from Canada and the United States. In Canada, we discovered multiple modes of convergent evolution: in one locality, resistance appears to have evolved through introductions of preadapted US genotypes, while in another, there is evidence for the independent evolution of resistance on genomic backgrounds that are historically nonagricultural. Moreover, resistance on these local, nonagricultural backgrounds appears to have occurred predominantly through the partial sweep of a single haplotype. In contrast, resistant haplotypes arising from the Midwestern United States show multiple amplification haplotypes segregating both between and within populations. Therefore, while the remarkable species-wide diversity of
A. tuberculatus
has facilitated geographic parallel adaptation of glyphosate resistance, more recently established agricultural populations are limited to adaptation in a more mutation-limited framework.
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