High detectability costs select weak warning signals in chemically defended gregarious prey

Area of Science:

• Ecology
• Evolutionary Biology
• Animal Behavior

Background:

• The evolution of costly chemical defenses in prey is counterintuitive, as conspicuousness typically aids predator learning and avoidance.
• This study investigates why prey with chemical defenses might evolve weak visual signaling strategies.

Purpose of the Study:

• To test hypotheses explaining weak visual signaling in chemically defended prey.
• To examine the role of predator community diversity, prey distinguishability, and gregariousness in signaling strategies.
• To investigate the survival costs of conspicuousness in European pine sawfly larvae.

Main Methods:

• Manipulated conspicuousness (solitary/grouped, cryptic/conspicuous coloration) of European pine sawfly larvae (Neodiprion sertifer).
• Assessed larval survival against predators in field experiments.
• Analyzed the conspicuousness of the larvae's ventral side during defense displays and its correlation with chemical defenses.

Main Results:

• Increased conspicuousness significantly decreased larval survival.
• The ventral side displayed during defense was more conspicuous (higher luminance) than when not displayed.
• Ventral side conspicuousness was not correlated with chemical defense levels.

Conclusions:

• Weak visual signaling strategies, despite chemical defenses, may be adaptive due to survival costs associated with conspicuousness.
• Gregariousness and synchronous displays involving defensive secretions may function as deterrent signals.
• Further research is needed to understand the mechanisms of weak visual signals in nature.