Local adaptation mosaic to leaf herbivores in the annual herb Datura stramonium

Local adaptation is a central evolutionary process for creating/maintaining variation of traits mediating antagonistic interactions. However, few studies have evaluated the local adaptation of plants to their biological counterparts such as herbivores across the plants' distribution. Most studies evaluating local adaptation to herbivores have focused on specialist systems, where local adaptation is likely to occur. However, there is less evidence regarding the existence of local adaptation on generalist systems, where local adaptation is not theoretically expected. We conducted a reciprocal transplant experiment involving four local populations aimed to detect whether local adaptation in the annual herb Datura stramonium to its specialist herbivore Lema daturaphila and the generalist herbivore Sphenarium purpurascens occur. We also explored whether leaf trichome density, a putative defensive trait of D. stramonium, is mediating local adaptation to herbivores through its association with plant fitness. We found that certain D. stramonium populations were locally adapted to both herbivores but others were not, regardless of whether these are preyed upon by generalist or specialist herbivores. Leaf trichome density had a significant effect on individual fruit production, although this effect was variable across locations (origin × site interaction) and unrelated to the observed local adaptation pattern. The results support a view of a local adaptation mosaic of D. stramonium to generalist and specialist herbivores in central Mexico.