Monthly Archives: June 2017
Are gregarious red-black shieldbugs, Graphosoma lineatum (Hemiptera: Pentatomidae), really aposematic? An experimental approach
Petr Veselý, Silvie Veselá, Roman Fuchs, Jan Zrzavý
Hypothesis: The coloration of the red-black shieldbug has a warning function. This quality
can be lowered when the shieldbug is presented on a fragmented background.
Organism: We offered wild-coloured and artificially deaposematized (painted brown) red-black shieldbugs (Graphosoma lineatum) to avian predators (Parus major, Parus caeruleus).
Site of experiments: The experiments were conducted in a cage (0.7 m × 0.7 m × 0.7 m) fitted with a one-way mirror.
Methods: In succession, we offered five shieldbugs to each bird. We presented the shieldbugs on contrasting (white) and matching (imitating the shieldbug’s habitat and imitating the striated shieldbug pattern) backgrounds.
Results: The blue tits avoided all shieldbugs offered to them regardless of their coloration. The great tits attacked both colour forms, but the brown one more frequently. The wild-coloured shieldbugs were significantly better protected against repeated attacks. Shieldbugs presented on any of the matching backgrounds were attacked less frequently than when presented on the white background.
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Newly emerged Batesian mimicry protects only unfamiliar prey
Petr Veselý, Roman Fuchs
The evolution of Batesian mimicry was tested experimentally using avian predators. We investigated the effect of a search image on the protection effectiveness of a newly emerged Batesian mimic. The two groups of predators (adult great tits, Parus major) differed in prior experience with prey from which the mimic evolved. The Guyana spotted roach (Blaptica dubia) was used as a palatable prey from which the mimic emerged, and red firebug (Pyrrhocoris apterus) was used as a model. Optical signalization of the insect prey was modified by a paper sticker placed on its back. The cockroaches with the firebug pattern sticker were significantly better protected against tits with no prior experience with cockroaches. The protection of the firebug sticker was equally effective on cockroaches as it was on firebugs. The cockroaches with firebug stickers were not protected against attacks of tits, which were familiar with unmodified cockroaches better than cockroaches with a cockroach sticker. We suppose that pre-trained tits acquired the search image of a cockroach, which helped them to reveal the “fake” Batesian mimic. Such a constraint of Batesian mimicry effectiveness could substantially decrease the probability of evolution of pure Batesian mimic systems.
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What constitutes optical warning signals of ladybirds (Coleoptera: Coccinellidae) towards bird predators: colour, pattern or general look?
Michaela Dolenská, Oldřich Nedvěd, Petr Veselý, Monika Tesařová, Roman Fuchs
Most ladybirds (Coleoptera: Coccinellidae) possess chemical protection against predators and signal its presence by less or more conspicuous coloration, which can be considered as a warning. Most ladybirds possess a dotted pattern, althougn the number, shape, and size of the spots, as well as their colour, varies considerably. Almost all ladybirds have a characteristic general appearance (body shape). We considered these traits to be used in ladybird recognition by avian predators. In the present study, we compared the reactions of avian predators (Parus major) caught in the wild, to four differently coloured ladybird beetles (Coccinella septempunctata, Exochomus quadripustulatus, Subcoccinella vigintiquatuorpunctata, and Cynegetis impunctata) and two artificial modifications of C. septempunctata; the first was deprived of their elytral spotted pattern by painting it brown, the other had their elytra removed (i.e. altering their general ladybird appearance). Ladybirds with a spotted pattern were attacked less frequently than unspotted ones. Ladybirds with removed elytra were attacked much more often than any ladybird with a preserved general appearance. The results obtained in the present study suggest the high importance of the spotted pattern as well as general appearance in the ladybird recognition process. Additional experiments with naïve birds (hand-reared P. major) demonstrated the innateness of the aversion to two differently spotted ladybird species (C. septempunctata and Scymnus frontalis).
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The role of size and colour pattern in protection of developmental stages of the red firebug (Pyrrhocoris apterus) against avian predators
Milena Prokopová, Petr Veselý, Roman Fuchs, Jan Zrzavý
We investigated how predator/prey body-size ratio and prey colour pattern affected efficacy of prey warning signals. We used great and blue tits (Parus major and Cyanistes caeruleus), comprising closely related and ecologically similar bird species differing in body size, as experimental predators. Two larval instars and adults of the unpalatable red firebug (Pyrrhocoris apterus), differing in body size and/or coloration, were used as prey. We showed that prey body size did not influence whether a predator attacked the prey or not during the first encounter. However, smaller prey were attacked, killed, and eaten more frequently in repetitive encounters. We assumed that body size influences the predator through the amount of repellent chemicals better than through the amount of optical warning signal. The larger predator attacked, killed and ate all forms of firebug more often than the smaller one. The difference between both predators was more pronounced in less protected forms of firebug (chemically as well as optically). Colour pattern also substantially affected the willingness of predators to attack the prey. Larval red–black coloration did not provide a full-value warning signal, although a similarly conspicuous red-black coloration of the adults reliably protected them.