Consequences of the overproduction of methyl jasmonate on seed production, tolerance to defoliation and competitive effect and response of Arabidopsis thaliana.

* Accumulation of methyl jasmonate (MeJA) after herbivore attack in plants is associated with the induction of defenses that can benefit fitness, but are costly to express; effects often explored using exogenous application of jasmonates. * Here I explored the consequences of the overexpression of MeJA on seed production, tolerance to defoliation and competitive effect and response, using a genotype of Arabidopsis thaliana that overexpresses jasmonic acid carboxyl methyltransferase (JMT) and contains threefold higher levels of MeJA than wild-type plants. * Without competition, JMT plants produced 37-40% less total seed mass than vector controls or wild-type plants, and had reduced seed germination. Defoliation reduced height more strongly in wild-type than in JMT plants, but reduced total seed production equally. In a competition experiment, the presence of a neighbor reduced fitness more strongly in wild-type than in JMT plants, but JMT plants exhibited dampened opportunity costs and benefits of induction with jasmonic acid of itself or its neighbor. This may have related to the higher constitutive expression but reduced inducibility of jasmonate-mediated defenses, including trypsin inhibitors, exhibited by JMT plants. * In natural plant populations, overexpression of MeJA-mediated responses should be beneficial to resistance to herbivores, pathogens and competitors, but is directly costly to fitness and probably constrains plasticity in response to changing environmental conditions.