local adaptation

Hall MC, Lowry DB & Willis JH 2010 Is local adaptation in Mimulus guttatus caused by trade-offs at individual loci? Mol Ecol 19:2739-2753.

  • local adaptation is largely controlled by non-overlapping loci
  • reduced gene flow prevents the evolution of individuals adapted to multiple environments
  • local adaptation could theoretically arise from allelic trade-offs at individual loci (i.e. antagonistic pleiotropy), with alleles in their native habitat having higher fitness than foreign alleles
  • alternatively, local adaptation could be caused by multiple independent loci, where native alleles at some loci are favoured over non-native alleles in one habitat and these alleles are selectively equivalent in the alternate habitat (i.e. conditional neutrality)
  • this latter pattern might only be expected to occur between populations linked by little or no migration
  • even modest rates of gene flow and recombination would be expected to facilitate the homogenization of the populations, with fixation of the conditionally beneficial alleles
  • our study is the first that we are aware of where there appears to be a genetic trade-off at an individual locus (DIV2) contributing to local adaptation
  • our study also provided many more potential examples of conditional neutrality where native alleles are favoured at one site and selectively neutral at another site
  • to date, there has been evidence of QTL by environment interactions due to conditional neutrality
  • all of these previous studies focused on selfing organisms, where limited recombination between populations could favour the maintenance of allelic variation at separate loci involved in local adaptation
  • in an outcrosser such as M. guttatus, however, even limited gene flow or recombination would facilitate the fixation of conditionally beneficial alleles
  • it is therefore striking that we also found evidence for conditional neutrality at several individual traits
  • trade-offs at individual loci across habitats is an implicit assumption of genomic scans for adaptive loci