1 Abstract Aim of the present study was to test antipredatory function of fulguration (or flash display), which means sudden exposition of conspicous body part on otherwise cryptic animal during escape. Adult squash bugs (Coreus marginatus; Heteroptera) were used as model prey, while as model predator served two species of passerine birds - blue tit (Cyanistes caerulus) and great tit (Parus major). Three approaches were undertaken. Test of palatability should have assessed the efficiency of squash bug chemical defence against bird predators. Experiment was carried out in experimental cage without interference of experimenter and without occurrence of fulguration. The results show that chemical defense of squash bug is less efficient than defense of other species of true bugs (Pyrrhocoris apterus, Graphosoma lineatum) and that the efficiency differs between two generations of squash bugs. In the test of efficiency of fulguration, the prey was forced by experimenter to fly in response to bird attack. Blue tits attacked the immobile prey more often than the flying and fulgurating one, but the same relation wasn't significant with great tits. The latencies of birds' returns to the bugs that landed after fulguration wasn't influenced by colour of the bugs' abdomen. Third experiment consisted of computer...

Jan Raška: Reactions of the jumping spider Evarcha arcuata to aposematic true bugs Abstract: This paper studies the effect of qualities of a prey on predatory behaviour of Evarcha arcuata (Araneae: Salticidae). Naturally coloured aposematic larveae of Pyrrhocoris apterus have been compared to two types of prey: 1) to identically coloured but in defensive secretion different larvae of Scantius aegyptius, and 2) differently coloured larvae of white mutants of P. apterus. The defensive secretion of S. aegyptius has been found less effective in the first interaction with predator than that of P. apterus, however, after several trials the difference of reactions of the spider has not been noticeable. When changed the species of prey, E. arcuata has symmetrically and considerably generalised between the two species. Significant difference has been established in memory test - while P. apterus has been avoided even after one day, S. aegyptius has been attacked as thought the spiders were naive. The learning sequence has been similar in both colour forms of P. apterus; the generalisation of the two colours has been symetrical as well. Both colour forms succeeded in memory test (e.g. spiders have proven difference in comparison with the naive ones), however, white mutants have been successfully attacked...

Aposematic signals advertise chemical defense or other forms of unprofitability to predators and may be parasitized by dishonest signallers through Batesian mimicry. Warning signals do not provide perfect avoidance, however, meaning many aposematic phenotypes evolve to balance between signal saliency and mitigating detection. For Batesian mimics the cost of a predator encounter should be greater, which begs the question of whether imperfect mimicry leads Batesian mimics to exhibit more muted signals than their models. I sought to test this hypothesis and other related hypotheses using the Ameerega-Allobates poison frog mimicry complex native to the Ecuadorian Amazonian rainforest. In Chapter 2 I found that, while many elements of the mimic’s signal were less salient than in the model, the mimic had higher detectability than the model. I also found that saliency discrepancies across colour patches produced variation in detectability across different body postures and viewing angles in both species. In Chapter 3 I turned my focus to how the balance between cryptic and salient signal elements changes across ontogeny, and how shifts in that balance may affect detectability. I found that both species undergo ontogenetic colour change, with the mimic improving in resemblance to the model as it developed and the model refining its aposematic signal as it grew. These colour changes impacted the crypsis efficacy of the mimic in that different colour stages had differential detectability. In Chapter 4 I tested for behavioural associations with the ontogenetic increase in mimetic fidelity in Al. zaparo. I found that colouration alone did not explain variation in behaviour, and that body size and environmental conditions impacted boldness and activity. / Dissertation / Doctor of Philosophy (PhD) / Antipredator colouration can take many different forms and can function according to different underlying strategies. Crypsis, also known as camouflage, operates by evading detection – effective crypsis means that predators don’t see the prey in the first place, increasing the prey’s survival. Using crypsis as an antipredator strategy means that a species should only occupy space where its colours blend in, however, and when hiding from predators it’s difficult to attend to other ecological needs like foraging, conquering and/or defending territory, or pursuing reproduction. These opportunity costs are thought to be reduced under aposematism, or ‘warning colouration’, where an animal evolves bright colouration that advertises some sort of secondary defense like toxic stings or secretions. Aposematic protection stems from standing out in the environment and being distinguishable from other prey, providing reduced predator attention across contexts such as foraging, reproduction, thermoregulation, or simple movement throughout the environment. These benefits can then be parasitized by a dishonest ‘mimic’ species which has no chemical defense but copies the warning signal of a ‘model’. Warning signal protection isn’t perfect, however, and most aposematic species still experience some form of predation threat. This means that there may be a limit to how conspicuous a signal an aposematic species is favoured to evolve. Accordingly, evidence shows that aposematic species incorporate both cryptic and aposematic elements into their colouration. The aim of this thesis is to examine how this balance is achieved by a poison frog and a non-toxic mimic, how this balance may change across development, and whether there are behavioural implications of changes in colour strategy. I found that both species have evolved a salient colour patch that they can flexibly expose or hide to modulate their detectability. I also found that the balance between crypsis and aposematism in the mimic and model shifts over time through developmental colour change. Lastly, I found that body size and environmental conditions affect behaviour in developing individuals of the mimic species.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2017-09-19T12:30:06Z No. of bitstreams: 2 Dissertação - Nathalia Ximenes Gonçalves - 2017.pdf: 11960098 bytes, checksum: a70e468c7f0aec1f54681daa44779319 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-09-19T12:30:25Z (GMT) No. of bitstreams: 2 Dissertação - Nathalia Ximenes Gonçalves - 2017.pdf: 11960098 bytes, checksum: a70e468c7f0aec1f54681daa44779319 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-09-19T12:30:25Z (GMT). No. of bitstreams: 2 Dissertação - Nathalia Ximenes Gonçalves - 2017.pdf: 11960098 bytes, checksum: a70e468c7f0aec1f54681daa44779319 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-08-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The sensory drive theory predicts that signals, sensory systems, and signaling behavior should coevolve. Variation in the sensory systems of prey and predators may explain the diversity of color signals, such as color polymorphism. The spider Gasteracantha cancriformis (Araneidae) possesses several conspicuous color morphs. The aim of the present study was to assess whether the color polymorphism of G. cancriformis may be maintained by pressure from multiple signal receivers, such as prey and predators with distinct color vision systems. In orb-web spiders, the prey attraction hypothesis states that conspicuous colors are prey lures that increase spider foraging success via flower mimicry. However, in highly defended species, conspicuous colors could also be a warning signal to predators. We used color vision modelling to estimate chromatic and achromatic contrast of G. cancriformis morphs as perceived by potential prey and predator taxa. To assess the role of prey, we conducted a prey capture experiment in the field, in which webs were assigned to four treatments: yellow, red, and black models, or no model. For each treatment, we counted the number of prey trapped on the webs and the calculated webs damaged area. To assess the role of predators on the evolution of conspicuous color patterns and polymorphism, we conducted a second field experiment, allocating yellow, red and black spider models in nylon threads along the vegetation, and observed the number of attack markings for each of them. Our results revealed that individual prey and predator taxa perceive the conspicuousness of morphs differently. Therefore, the multiple prey and multiple predator hypotheses may explain the evolution of color polymorphism in G. cancriformis. The results of prey capture experiment did not corroborate the prey attraction hypothesis nor the prey specific adaptation of color polymorphism. On the predation experiment, we found that black spider models presented more markings, which indicates that yellow and red models were less preferred, possibly suggesting that spider coloration may play a role on predator avoidance. Our results, however, do not corroborate the hypothesis that multiple predators influence polymorphism evolution. Color polymorphism in this species is possibly a multi-functional attribute, where some morphs benefits from aposematism, whereas others may alternative fitness advantages. Non-adaptive explanation should also be considered in future experiments of the evolution and maintenance of color polymorphisms. / A teoria de “sensory drive” prediz que sinais, sistemas sensoriais e comportamentos de sinalização devem coevoluir. Variação no sistema sensorial de presas ou predadores pode explicar a diversidade de colorações existentes e polimorfismos de cores. A aranha de teia orbicular Gasteracantha cancriformis apresenta padrões de coloração conspícuos e polimorfismo de cor. A evolução e manutenção de tal variação cromática pode ser influenciada por presas e predadorescom sistemas visuais diferentes, já que um mesmo morfo é percebido distintamente por potenciais presas e predadores. A coloração conspícua, entretanto, não se assemelha à coloração de flores. Tampouco influencia na captura de presas, visto que modelos dessa aranhas apresentaram números similares de presas nas teias. Portanto, ao contrário de outras aranhas de teia orbicular, para as quais a coloração chamativa é atribuída ao mimetismo floral, para G. cancriformis, esta hipótese não é corroborada. Os morfos amarelo e vermelho apresentam coloração típica de organismos aposemáticos e são conspícuos para a visão de uma ave. O morfo vermelho apesar de não ser conspícuo na visão de vespas, ainda assim poderia estar protegido de predação por camuflagem. Dessa forma, esses morfos poderiam ser mantidos na população devido à pressão de diferentes predadores, morfos vermelhos sinalizariam impalatabilidade para aves, enquanto morfos amarelos, para vespas. Porém, essas diferenças não foram observadas experimentalmente. Em campo, modelos pretos de aranha apresentaram mais marcas de predação do que modelos amarelos e vermelhos, também sugerindo que em G. cancriformis a coloração chamativa pode ser um sinal de advertência para predadores. Porém, a multiplicidade de predadores por si só não explica a variação cromática em populações dessa espécie de aranha. Consequentemente, o polimorfismo de cor em G. cancriformis pode ser uma característica multi-funcional, onde morfos não aposemáticos seriam mantidos nas populações devido a outras funções adaptativas, como camuflagem ou termorregulação.

This thesis focuses on various factors affecting effectiveness of aposematic signals against avian predators. Adult, wild-caught as well as hand-reared juvenile great tits (Parus major) were used as predators in the experiments. The thesis consists of the following four studies. In the first study, we compared the reactions of great tits from two geographically distant populations toward aposematic firebugs (Pyrrhocoris apterus) and their non-aposematic artificially made colour variant. The birds from the Bohemian population mostly avoided aposematic firebugs and attacked non-aposematic variant. Finnish birds, which lacked experience with firebugs from their natural environment, were less hesitant to attack both firebug colour forms. Although the Bohemian birds avoided the aposematic prey variant, they were not more neophobic than Finnish birds. We conclude that the geographic differences in reactions of the birds to aposematic prey can be explained by a different population-specific experience of the birds with local aposematic prey communities. In the second study, we compared effectiveness of two chemical defence strategies in leaf beetle larvae (Chrysomela lapponica) against great tits. The birds avoided larvae devoid of external secretions after the first attack, which indicates the presence...