Tritrophic Interactions Flashcards
Plant defensive metabolites can impact parasitoid success via several mechanistic routes. Describe these routes.
(I) Developing parasitoid larvae are directly exposed when toxins infiltrate the host’s hemolymph, resulting in reduced growth and survival, for example.
(II) Defenses reduce herbivore developmental rate, resulting in smaller hosts with correspondingly fewer adult parasitoids emerging.
(III) Defensive chemistry affects the nature and/or magnitude of host immune responses to immature parasitoids.
Define a trophic level.
A trophic level is defined as a shared energy level of organisms with the same consumption modes within an ecosystem. The organisms between/within these levels are connected by food chains to produce food webs.
Explain the monarchs “self-medication”.
The protozoan parasite O.s elektroscirrha infects larvae of the monarch butterfly. In the absence of the parasite, cardenolides (a type of chemical plant defense in milkweeds) reduce monarch lifespan. However, cardenolides kill the parasites in the hemolymph, and in the presence of the parasite cardenolides increase the lifespan of monarch butterflies. Female monarchs lay more eggs on high-cardenolide species of milkweed if they are infected with the parasite, but show reduced preference for high-cardenolide milkweeds if they are not infected.
Describe the physiological process that created the ‘antispider’ signal in hornworms against wolf spiders.
In Manduca sexta, the enzyme MsCYP6B46 redirects a small amount of nicotine from ingested wild tobacco from the midgut into hemolymph, from which nicotine is exhaled through the spiracles as an ‘antispider’ signal. CYP6B46-silenced larvae were more susceptible to spider-attack because they exhaled less nicotine due to lower hemolymph concentrations.
How do extrafloral nectaries and emission of volatile compounds act as indirect defenses for plants?
Plants containing extrafloral nectaries had much less herbivores present and significantly higher percentage of larvae and pupae parasitized than those without extrafloral nectaries. When plants recognize herbivore-associated elicitors, they produce and release a blend of volatiles that can attract predators, parasites, and other natural enemies.
What is a “tritrophic interaction” and give two examples?
Tritrophic interactions, as they relate to plant defense against herbivory, describe the ecological impacts of three trophic levels on each other: the plant, the herbivore, and its natural enemies, predators/parasitoids of the herbivore. The parasite larvae of A. congregatus, an important enemy of hornworms, died due to the presence of nicotine on hornworms that feed upon dark-fired tobacco. Concentrations of nicotine also caused significant mortality on C. congregata, another parasitoid of horworms.
