Plant ontogeny and species interactions: chemical defense and herbivore preference and performance depend on host-plant age

QUINTERO C

Galveston, TX

Conferencia; Gordon Conference in Plant-Herbivore Interactions; 2010

Gordon Research Conferences

Resource allocation constraints throughout plant ontogeny have been shown to affect the expression of numerous plant traits relevant to herbivores, such as nutritional content and physical and chemical defenses. However, we know little about how these plant traits changes across multiple developmental stages of a plant species or how herbivore species respond to those changes. In order to evaluate how oviposition preferences and caterpillar performance vary among multiple developmental stages of the same host plant, Buckeye butterflies (Junonia coenia Hubner, Nymphalidae) were exposed to greenhouse Plantago lanceolata L. (Plantaginaceae) plants of five distinct ontogenetic stages. Two choice tests were performed: 6 vs. 8 vs. 10 wks-old plants and 10 vs. 14 vs. 18 wks-old plants. After 72hrs, total number of eggs on each of the three plants was recorded. To evaluate caterpillar performance, one newly-hatched larva was placed on each of 20 plants per ontogenetic stage. Larvae were monitored and weighed every five days from 2nd instar to pupation, and survival rate, growth rate, developmental time, and pupa weight determined. Plant age significantly influenced both butterfly oviposition choice and caterpillar performance. Buckeye butterflies greatly prefer younger developmental stages of P. lanceolata over older plant stages. In accordance with the "mother knows best" hypothesis, caterpillars also performed better on younger developmental stages. Mortality rate significantly varied depending on host-plant age, ranging from 5% to 100% for caterpillars reared on seedlings to post-reproductive stages. In addition, surviving caterpillars developing on seedling plants developed significantly faster, achieved higher growth rates, and reached higher pupal weights than caterpillars on older plant stages. Decreases in caterpillar performance was significantly related to increases in plant physical and chemical defenses as well as decreases in plant quality as host-plants aged. These results demonstrate that changes in plant traits throughout plant development can greatly influence insect herbivores by directly altering herbivore preference and performance. Because Buckeye caterpillars sequester iridoid glycosides from their host plants, changes in plant traits associated with plant ontogeny may also indirectly alter herbivore predation risk. Thus, my findings suggest that plant ontogeny may play a more critical role in mediating multitrophic interactions than previously thought.