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

The evolution of costly chemical defenses in cryptic prey is puzzling, as
conspicuousness should be adaptive for defended prey by enhancing predator
avoidance learning. Here, we explore three hypotheses that may promote
weak visual signal strategies: (1) Low prey conspicuousness is favored in
diverse predator communities; (2) Conspicuousness is less critical if
color patterns or behavior allow defended prey to be distinguished from
cryptic prey; and (3) in gregarious prey species, aggregation itself could
act as a deterrent signal. We used chemically defended and gregarious
European pine sawfly (Neodiprion sertifer) larvae, exhibiting
green-black-grey coloration, as our study system. First, we manipulated
the conspicuousness of the larvae by placing them either solitarily or in
groups and marking them with either cryptic or conspicuous coloration,
then testing their survival against predators in the field. Second, we
analyzed how conspicuous the ventral side (which larvae reveal during a
defense display) of N. sertifer appears to avian predators and how its
conspicuousness correlates with the larvae's chemical defenses. Our
results indicate that increased conspicuousness was costly and decreased
larvae survival. The ventral side of larvae making the defense display was
more conspicuous (showed higher luminance) than that of larvae not
displaying; however, this was not associated with chemical defense traits.
The signaling function of synchronous displays involving defensive
secretions in sawflies presents a promising avenue for future studies on
the mechanisms by which weak visual signals operate in nature.