Genomic and chemical evidence for local adaptation in resistance to different herbivores in Datura stramonium

Since most species are collections of genetically variable populations
distributed to habitats differing in their abiotic/biotic environmental
factors and community composition, the pattern and strength of natural
selection imposed by species on each others' traits are also expected
to be highly spatially variable. Here, we used genomic and quantitative
genetic approaches to understand how spatially variable selection operates
on the genetic basis of plant defenses to herbivores. To this end, an F2
progeny was generated by crossing Datura stramonium (Solanaceae) parents
from two populations differing in their level of chemical defense. This F2
progeny was reciprocally transplanted into the parental plants’ habitats
and by measuring the Identity by Descent (IBD) relationship of each F2
plant to each parent, we were able to elucidate how spatially variable
selection imposed by herbivores operated on the genetic background (IBD)
of resistance to herbivory, promoting local adaptation. The results
highlight that plants possessing the highest total alkaloid concentrations
(sum of all alkaloid classes) were not the most well-defended or fit.
Instead, specific alkaloids and their linked loci/alleles were favored by
selection imposed by different herbivores. This has led to population
differentiation in plant defenses and thus, to local adaptation driven by
plant-herbivore interactions.