Abstract
Predation has driven the evolution of diverse adaptations for defence among prey, and one striking example is the deimatic display. While such displays can resemble, or indeed co-occur with, aposematic ‘warning’ signals, theory suggests deimatic displays may function independently of predator learning. The survival value of deimatic displays against wild predators has not been tested before. Here we used the mountain katydid Acripeza reticulata to test the efficacy of a putative deimatic display in the wild. Mountain katydids have a complex defence strategy; they are camouflaged at rest, but reveal a striking red-, blue-, and black-banded abdomen when attacked. We presented live katydids to sympatric (experienced) and allopatric (naive) natural predators, the Australian magpie Cracticus tibicen, and observed bird reactions and katydid behaviors and survival during repeated interactions. The efficacy of the katydids’ defence differed with predator experience. Their survival was greatest when faced with naïve predators, which provided clear evidence of the protective value of the display. In contrast, katydid survival was consistently less likely when facing experienced predators. Our results suggest that sympatric predators have learned to attack and consume mountain katydids despite their complex defense, and that their post-attack display can be an effective deterrent, particularly against naïve predators. These results suggest that deimatism does not require predator learning to afford protection, but that a predator can learn to expect the display and subsequently avoid it or ignore it. That sympatric predators learn to ignore the defense is a possible explanation for the mountain katydid’s counter-intuitive behavior of revealing warning colors only after tactile stimuli from predator attack.
Highlights
The study of visually conspicuous defensive signals has driven the development of fundamental evolutionary theory in predator-prey interactions[1,2], mimicry[3,4,5], cognition[6] and speciation[3,7,8]
It has been predicted that due to its sudden transition, deimatism does not require predators to accumulate experience, and that its protective value is greater against inexperienced predators compared to that of aposematism[17]
We examined the responses of a known avian predator to an insect in assays designed to quantify both the absolute and relative protective value of the display across natural variation in predator experience
Summary
The study of visually conspicuous defensive signals has driven the development of fundamental evolutionary theory in predator-prey interactions[1,2], mimicry[3,4,5], cognition[6] and speciation[3,7,8]. Of their display could decrease as a function of predator experience, if predators learn to suppress their aversive response[27] This effect may be ameliorated by the presence of further co-occurring defences, such as an aposematic element combined with a deimatic element. If the display exploits a reflexive response in the predator, which does not require learned aversion, we predicted that upon first presentation naïve predators should be less likely to attack, kill, and eat the prey than experienced predators. We predicted that experienced predators would respond consistently between their first and second encounter with katydids, while naïve predators would attack the unknown prey on their first interaction and, once startled, abandon the hunt. We expected previously naïve predators to either: (a) avoid the insect, if they learned to associate the display (and/or co-occurring defence) with unprofitability; or (b) attack the insect, if they learn to expect the display and the insect is sufficiently profitable prey
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