Hard to catch: experimental evidence supports evasive mimicry

Abstract

Most research on aposematism has focused on chemically defended prey, but the signalling difficulty of capture remains poorly explored. Similar to classical Batesian and Müllerian mimicry related to distastefulness, such ‘evasive aposematism' may also lead to convergence in warning colours, known as evasive mimicry. A prime candidate group for evasive mimicry are Adelpha butterflies, which are agile insects and show remarkable colour pattern convergence. We tested the ability of naive blue tits to learn to avoid and generalize Adelpha wing patterns associated with the difficulty of capture and compared their response to that of birds that learned to associate the same wing patterns with distastefulness. Birds learned to avoid all wing patterns tested and generalized their aversion to other prey to some extent, but learning was faster with evasive prey compared to distasteful prey. Our results on generalization agree with longstanding observations of striking convergence in wing colour patterns among Adelpha species, since, in our experiments, perfect mimics of evasive and distasteful models were always protected during generalization and suffered the lowest attack rate. Moreover, generalization on evasive prey was broader compared to that on distasteful prey. Our results suggest that being hard to catch may deter predators at least as effectively as distastefulness. This study provides empirical evidence for evasive mimicry, a potentially widespread but poorly understood form of morphological convergence driven by predator selection.

Aposematism and mimicry in birds

“…Thirdly, there is evasive behaviour where an animal signals that its future flight from the predator will be too fast or agile for the predator to capture it (Páez et al . 2021); this is often a morphological signal that is invariant across individuals. If we include this wider ambit of aposematic‐like signals, we immediately recognize that there are actually many examples of aposematism in birds that have hitherto been overlooked.…”

Darwin’s Hawkmoth (Xanthopan praedicta) responds to bat ultrasound at sonar‐jamming rates

“…While sonar jamming is a likely function of this high‐density acoustic trait, it is also possible that X . praedicta's sounds act as a salient cue for different effect, such as warning predators of low capturability (i.e., evasive aposematism (Páez et al, 2021)). Alternatively, although palatability studies with hawkmoths have so far revealed a lack of chemical defense in the adult form (Kawahara & Barber, 2015), X .…”

“…The sphingine file and scraper strategy in general seems to produce similar effects across species, as X. praedicta and the two other representative genera (Figure 2; Barber & Kawahara, 2013) demonstrate some of the highest duty cycle, longest duration, and lowest dominant frequency sounds among described bat-responding moths (Figure 2). While sonar jamming is a likely function of this highdensity acoustic trait, it is also possible that X. praedicta's sounds act as a salient cue for different effect, such as warning predators of low capturability (i.e., evasive aposematism (Páez et al, 2021)).…”

Motion: enhancing signals and concealing cues

“… Maan and Cummings, 2012) or ease of capture (e.g. Páez et al, 2021) may also vary according to the movement of the signaller. Species-level comparisons across several different taxonomic groups reveal differences in colour patterns according to mobility: among lizards, species with striped colour patterns are more mobile than those with cryptic patterns ( Halperin et al, 2017 ); small, fast-moving snakes that hunt actively tend to have longitudinal stripes, while large, slow snakes that ambush hunt have blotched patterns ( Allen et al, 2013 ); longitudinal bands occur more frequently on the eye-lines of faster moving, slender fish species, and vertical bands occurred more frequently on sharply turning, deep-bodied fishes ( Barlow, 1972 ).…”