The evolution of plant response to herbivory: simultaneously considering resistance and tolerance in Brassica rapa

Pilson, D

D. Pilson, The evolution of plant response to herbivory: simultaneously considering resistance and tolerance in Brassica rapa, EVOL ECOL, 14(4-6), 2000, pp. 457-489

71

INGLESE

Article

Environment/Ecology

EVOLUTIONARY ECOLOGY

0269-7653 → ACNP

14

4-6

2000

457 - 489

ISI

0269-7653(2000)14:4-6<457:TEOPRT>2.0.ZU;2-P

Although the evolution of plant response to herbivory can involve either re sistance (a decrease in susceptibility to herbivore damage) or tolerance (a decrease in the per unit effect of herbivory on plant fitness), until rece ntly few studies have explicitly incorporated both of these characters. Mor eover, theory suggests these characters do not evolve independently, and al so that the pattern of natural selection acting on resistance and tolerance depends on their costs and benefits. In a genotypic selection analysis on an experimental population of Brassica rapa (Brassicaceae) I found a comple x set of correlational selection gradients acting on resistance and toleran ce of damage by flea beetles (Phyllotreta cruciferae: Chrysomelidae) and we evils (Ceutorhynchus assimilis: Curculionidae), as well as directional and stabilizing selection on resistance to attack by weevils. Evolution of resp onse to flea beetle attack is constrained by a strong allocation cost of to lerance, and this allocation cost may be caused by a complex correlation am ong weevil resistance, weevil tolerance, flea beetle resistance, and flea b eetle tolerance. Thus, one important conclusion of this study is that ecolo gical costs may involve complex correlations among multiple characters, and for this reason these costs may not be detectable by simple pairwise corre lations between characters. The evolution of response to weevil attack is p robably constrained by a series of correlations between weevil resistance, weevil tolerance, and fitness in the absence of weevil damage, and possibly by a cost of tolerance of weevil damage. However, the nature of these cons traints is complicated by apparent overcompensation for weevil damage. Beca use damage by both flea beetles and weevils had non-linear effects on plant fitness, standard measures of tolerance were not appropriate. Thus, a seco nd important contribution of this study is the use of the area under the cu rve defined by the regression of fitness on damage and damage-squared as a measure of tolerance.