Tritrophic interactions follow phylogenetic escalation and climatic adaptation

Area of Science:

• Plant evolutionary ecology
• Chemical ecology
• Ecosystem interactions

Background:

• Tritrophic interactions, involving plants, herbivores, and predators, are shaped by plant defenses.
• Phytochemicals and volatile organic compounds mediate these interactions, influencing ecosystem dynamics.
• Understanding variation in plant defenses across environments is crucial for evolutionary ecology.

Purpose of the Study:

• To test the resource-availability, altitudinal gradient, and defense escalation hypotheses in plant defense evolution.
• To investigate how environmental factors and phylogenetic history influence plant volatile production.
• To examine the role of belowground indirect plant defenses in alpine ecosystems.

Main Methods:

• Studied 18 Alpine Festuca grass species across a 2000-meter elevation gradient.
• Assessed predatory soil nematode attraction to root volatiles from damaged and intact roots.
• Analyzed volatile blends in relation to species' climatic niches and phylogenetic divergence.

Main Results:

• Adaptation to nutrient-limited alpine environments correlated with attractive volatile blends for nematodes.
• Recently diverged Festuca taxa released more volatiles when exposed to herbivores than ancestral species.
• Phylogenetic drivers supported the defense escalation hypothesis, while local adaptation supported the resource availability hypothesis.

Conclusions:

• Belowground indirect plant defenses in Festuca grasses have evolved under resource availability and defense escalation pressures.
• Environmental harshness and phylogenetic relatedness significantly influence the evolution of plant volatile-mediated defenses.
• This study provides evidence for the adaptive evolution of plant indirect defenses in response to ecological pressures.