Genetic variation in defensive chemistry in Plantago lanceolata (Plantaginaceae) and its effect on the specialist herbivore Junonia coenia (Nymphalidae)

Abstract

To examine genetic variation in defensive chemistry within and between natural populations of Plantago lanceolata, we performed a greenhouse experiment using clonal replicates of 15 genotypes from each of two populations, from a mowed lawn and an abandoned hayfield. Replicates of each genotype were harvested for determinations of aboveground biomass and leaf chemical content either at the beginning of the experiment (initial controls), after exposure to herbivory by larvae of Junonia coenia, a specialist on P. lanceolata (herbivory treatment), or at the end of the experiment without exposure to herbivory (final controls). Allocation to the iridoid glycosides aucubin and catalpol and the phenylpropanoid glycoside verbascoside displayed significant genetic variation within and between populations, and differed with leaf age. Significant genotypextreatment interactions indicated genetic variation in response of leaf chemistry to the treatments. There was no evidence for a cost of allocation to chemical defense: genetic correlations within and between chemical pathways and between defensive chemicals and aboveground growth were positive or nonsignificant. Although iridoid glycosides are known to be qualitative feeding stimulants for J. coenia, multiple regression of larval survivorship on leaf chemical content and shoot biomass indicated that larvae had lower survivorship on P. lanceolata ge-notypes with higher concentrations of aucubin in the leaves. Larval survivorship was unaffected by levels of catalpol and verbascoside. Thus, although specialist herbivores may respond to defensive chemicals as qualitative feeding stimulants, they do not necessarily have higher fitness on plant genotypes containing higher concentrations of these chemicals.

Fitness Costs of Chemical Defense in Plantago Lanceolata L.: Effects of Nutrient and Competition Stress

“…Our results are at variance with those of previous studies in P. lanceolata, in which no costs of IGs were detected in terms of a reduction in aboveground biomass or plant relative growth rate using phenotypic (Bowers and Stamp 1992;Darrow and Bowers 1997) or among-genotype correlations (Adler et al 1995) of plants that were grown outdoors. The reason for this discrepancy is unclear.…”

“…The reason for this discrepancy is unclear. The range of genotype means (about fivefold variation in IGs) among the 30 genotypes used in the study of Adler et al (1995) was roughly similar to the range among our 24 families. Possibly, the differential results reflect differences in genetic background of the material, their use of a field study (in contrast to our greenhouse study) that potentially results in higher variances in both biomass and defense levels, or their lower overall extent of reproduction, the stage in which costs in our study were most clearly expressed.…”

“…The biosynthetic costs of these IGs are high (Gershenzon 1994). However, in previous studies of P. lanceolata no costs of IGs could be detected in terms of negative among-genotype correlations between the level of IGs and aboveground biomass or plant growth (Adler et al 1995).…”

“…In The Netherlands, it is a common plant of roadsides and moist and dry grassland (Haeck 1992). Among the secondary plant compounds produced by P. lanceolata are the two IGs aucubin and catalpol (Duff et al 1965;Bowers and Stamp 1992;Adler et al 1995).…”

Intraspecific Variation in Plant Defense Alters Effects of Root Herbivores on Leaf Chemistry and Aboveground Herbivore Damage

“…As in previous studies (Marak et al 2003), plants from the "high-IG line" produced fewer flower stalks, but produced more root and leaf biomass than plants from the "low-IG line." Former studies also did not detect costs in terms of vegetative biomass for plants producing high levels of IG (Bowers and Stamp 1992;Adler et al 1995;Marak et al 2003). After placing half of the experimental plants for more than 3 months in the field, the root and remaining leaf biomass of the plant lines did not differ and were not affected by the wireworm treatment anymore.…”