The effectiveness of eyespots and masquerade in protecting artificial prey across ontogenetic and seasonal shifts

Abstract

When constraints on antipredator coloration shift over the course of development, it can be advantageous for animals to adopt different color strategies for each life stage. Many caterpillars in the genus Papilio exhibit unique ontogenetic color sequences: e.g., early instars that masquerade as bird feces, with later instars possessing eyespots. I hypothesize that larvae abandon feces masquerade in lieu of eyespots due to ontogenetic changes in signaler size. This ontogenetic pattern also occurs within broader seasonal shifts in background color and predator activity. I conducted predation experiments with artificial prey to determine how potential signaling constraints (specifically size and season) shape predation risk, and consequently the expression of ontogenetic color change in Papilio larvae. Seasonally, both predation and background greenness declined significantly from July to September, though there was little evidence that these patterns impacted the effectiveness of either color strategy. Caterpillar size and color strongly affected the attack rate of avian predators: attacks increased with prey size regardless of color, and eyespotted prey were attacked more than masquerading prey overall. These results may reflect a key size-mediated tradeoff between conspicuousness and intimidation in eyespotted prey, and raise questions about how interwoven aspects of behavior and signal environment might maintain the prevalence of large, eyespotted larvae in nature.

Attack rates on artificial caterpillars in urban areas are higher than in suburban areas in Colombia

“…One possibility is that the size of the model may favour attacks by birds. It has been observed that birds respond positively to increased prey size (Postema 2021), having a strong impact at the end of the larval period; whilst, the effect is the opposite in arthropods since these mainly attack small individuals (Feeny et al 1985, Lövei & Ferrante 2017, Remmel & Tammaru 2009, Remmel et al 2011). Barton (1986) observed that ants attack eggs and small larvae of P. sennae , while avoiding lepidopteran larvae larger than 10 mm.…”

“…These results are in agreement with those reported by Ferrante et al (2022) and Sam et al (2015) in other experiments using artificial larvae. Despite that, the general trend is for arthropods to be the main predators (Ferrante et al 2014, 2017a, 2021, Magagnoli et al 2018, Molleman et al 2016, Pena et al 2021. The fact that the most common markings found on models fitted those of birds does not mean that these are the main predators in urban environments.…”

Resolving the paradox of local warning signal diversity with predator learning

“…Field learning experiments present artificial prey to all potential predators in the community instead of targeting specific predator individuals or species (e.g., refs. [67][68][69][70][71][72][73][74]. Final attack probabilities, forgetting rates, and the strength of generalization can be derived from attack rates in the same way as the laboratory experiments.…”

Eyespot peek-a-boo: false eyes improve the survival of caterpillars in leaf rolls

“…This effect would fulfill the definition of a "momentary, transient signal" that startles a predator enough to slow or halt its attack (Umbers & Mappes 2016). Additionally, leaf rolls may offset potential detectability costs of large, conspicuous eyespots , Postema 2022. While the startling "conceal-then-reveal" effect of eyespots within leaf rolls has been presumed for both P. troilus larvae and other lepidopteran species (Wagner 2005;Janzen et al 2010), this assumption remains untested.…”