New home, new life: Tolerance to herbivores in Datura stramonium in a novel environment

Background/Question/Methods

To defend themselves from herbivores, plants rely on resistance and tolerance mechanisms. Both strategies imply allocation costs and may trade-off if redundant. Plant species that colonize new environments where their enemies are absent may reduce investments in resistance and rely on tolerance if damaged. In this study we assessed whether a plant species introduced into a different country where its specialist herbivores are absent is more tolerant than in its native range, and if genotype with higher relative growth rate (RGR) are more tolerant to damage. Our study system is Datura stramonium (jimsonweed), a plant species native to America (México) that is preyed upon by specialist chrysomelid beetles and a weevil. The Conquerors of Mexico brought Datura stramonium into Spain during the 16^th century, where it has no specialist herbivores. We assessed the tolerance response to damage in ten genotypes of four populations: Two native populations (Mexico) and two from Spain (introduced). Half the plants of each family were allocated to the damage or control treatments. At the onset of flowering, artificial damage (50% of total leaf area) was applied to plants in the experimental group. Damage was made of holes in the leaf blade as to mimic damage by the beetles. Growth measurements were taken from each plant (height, leaf area) periodically. At reproduction we obtained the total seed number per plant as an estimator of individual fitness. 

Results/Conclusions

Preliminary results show that plants from Spain have an average level of tolerance higher than plants from the native environment. Also, RGR of population introduced to Spain was higher than that from Mexican populations of D. stramonium. Plants from population La Zubia (Spain) had the highest tolerance, whereas plants from Teotihuacan (Mexico) had the lowest level. We did not detect genetic variance for the measured characters within populations. Results suggest that investment in tolerance could be less expensive than investment in resistance when the natural enemies are absent.