Mating system consequences on resistance to herbivory and life history traits in Datura stramonium

The consequences of selfing and outcrossing in Datura stramonium, a colonizing annual species, were experimentally assessed in terms of the fecundity of maternal plants and the performance of their progeny. Selfed and cross-pollinated plants were produced through controlled crosses and were then planted in their native environment. We recorded size at establishment, final height, number of branches, fruits, total biomass, and resistance to herbivores for each plant. Natural selection was measured for plant size and resistance to herbivores in both types of plants. Seed production (fecundity) was higher for fruits developed from outcrossing than for fruits derived from selfing. Among-family differences were detected for seed mass, but these were not related to mating system. No differences in germination, plant size, and fruit number were found between the two mating systems. Damage produced by two herbivores, Epitrix parvula and Sphenarium purpurascens, ranged from 0 to 95% of total leaf area; however, there were no differences in resistance to both herbivorous insects either among families or between mating systems. Plant survival through the whole season was similar for plants of both types of crossing. The direction and magnitude of phenotypic selection for each trait were similar for both types of progeny. Directional selection to increase plant size and reduce resistance to E. parvula was detected, while no selection was detected for resistance to S. purpurascens. Curvilinear (stabilizing/disruptive) and correlational selection modes were not detected for any trait. Inbreeding depression coefficients were all statistically indistinguishable from zero, except for seed number per fruit. The inbreeding depression coefficient for seed number was high and close to 40%, suggesting that evolution toward complete selfing may be prevented in this population of Datura stramonium.