Social learning in animals is a frequently studied topic, including birds. Great tits belong to frequently tested passerine species in this context. For this experiment we have chosen another tit species as model birds - adult and juvenile blue tits (Cyanistes caeruleus) and coal tits (Periparus ater). We tested an effect of social information on discrimination learning between palatable and unpalatable prey. Red and green artificial prey items resembling shieldbugs with a mealworm glued underneath were offered to birds. One variant was palatable, the other was unpalatable, soaked in bitter substance. Experimental groups were allowed to observe a pretrained tutor of the same species choosing palatable prey variant and rejecting the unpalatable one. The birds were then subjected to an individual discrimination learning task with simultaneously offered palatable and unpalatable prey items. The control group was not allowed to observe tutor and learned only individually. On the following day, all birds participated in a memory test. We tested if social information has an influence on avoidance learning in juvenile and adult birds of both species. We found that both species of tits were similarly successful in discrimination learning and there was no difference in success in performance between adult...

Aposematic animals advertise their defensive mechanisms to potential predators using warning signals. Signalling through more than one sensory pathway is called multimodal warning display. Most experimental studies of aposematism have been focused on the effect of a particular warning signal rather than on importance of multimodal signalling. Focusing on the multimodal signalling of real prey is the best way how to understand its effect in nature. The present study is focused on comparing the effect of multimodal warning display of insect prey with its particular warning signals on two species of bird predators. Multimodal warning signalisation of the burrowing bug, Tritomegas sexmaculatus consists of visual (black and white coloration), chemical (odour, possibly taste) and acoustic (stridulation) signals. We compared reactions of wild-caught great tit (Parus major) and blue tit (Cyanistes caeruleus) to three types of bugs with different warning displays. The non-manipulated bugs displayed multimodally, the brown painted bugs had their warning coloration manipulated and the dealatized bugs couldn't emit acoustic signals. The wild-caught birds of both species avoided all types of bugs. In an experiment with naive hand reared great tits we compared their reactions to non-manipulated and dealatized bugs. Naive...

The introductory part of this thesis sums up the state of knowledge on aposematism and mimicry, the effect of aposematic and mimetic signals on spider predators, and cases when spiders do not receive but send such signals. Attachments of the thesis include four original manuscripts. In the first study, we presented jumping spiders (Evarcha arcuata, Salticidae) with different colour forms (red-and-black, yellow-and-black, white-and-black) of the firebug (Pyrrhocoris apterus, Pyrrhocoridae). Our goal was to compare reactions of the spiders to various intensity of aposematic signalization, expecting red-and-black coloration to have the strongest effect. Aversive learning of all colour forms was equally effective, but generalization of the learned avoidance to other colour forms was more effective after switch from less (white-and-black, yellow-and-black) to more (red-and-black) conspicuously coloured prey. When tested the next day, avoidance of the white-and-black prey got mostly forgotten. In the second study, we assessed little studied sensitivity of spiders to smells of unpalatable prey. After jumping spiders learned to avoid firebugs, most of them avoided the firebug smell, showing their sensitivity not only to optical, but also to chemical part of signalization of the unpalatable prey. In the...

La diversification des signaux aposématiques dans un cadre de mimétisme müllérien est un phénomène intrigant. Alors que la théorie relative à l'aposématisme et au mimétisme suggère l'évolution vers un signal aposématique unique, d'impressionnantes variations peuvent être observées entre les populations, et cela à petite échelle spatiale. Il a été supposé que la variation spatiale des pressions de sélection engendrées par différents prédateurs puisse être à l'origine de ce phénomène. Afin de tester cette hypothèse, nous avons étudié la transition entre deux systèmes géographiques caractérisés par des patrons aposématiques distincts chez des grenouilles mimétiques et toxiques du nord du Pérou (Dendrobatidae) en combinant les outils de génétique des populations aux outils écologiques. Dans chacun de ces systèmes, Ranitomeya imitator vit en sympatrie avec R. ventrimaculata ou R. variabilis. Il s'agit du principal exemple empirique suggérant que dans un cadre de mimétisme müllérien, il n'y a pas convergence des signaux aposématiques des deux espèces, mais plutôt convergence unidirectionnelle où R. imitator, étant polymorphe, imite des espèces monomorphes avec lesquelles elle est sympatrique. Premièrement, les résultats réfutent les prémisses qui suggèrent que R. imitator converge vers le signal aposématique d’une autre espèce. La haute similarité génétique entre les espèces modèles suggère qu'elles ont divergé plus récemment que les populations de R. imitator ou qu'elles sont encore connectées par du flux génique. Ces résultats indiquent que ces espèces ont été identifiées à tort comme des espèces différentes. De fait, l'identification de l'espèce imitatrice basée sur la variabilité phénotypique est invalidée dans ce système puisque R. imitator et R. variabilis/ventrimaculata démontrent la même variabilité. Deuxièmement, nos résultats démontrent que la prédation varie spatialement, autant en intensité qu'en direction, créant ainsi un paysage hétérogène de pressions de sélection. Ainsi, de fortes pressions de prédation stabilisatrice permettent le maintien de l'organisation géographique de différents signaux aposématiques et expliquent l'uniformité de ces signaux ainsi que les relations mimétiques. Par contre, le relâchement temporaire des pressions de prédation permet l'apparition de nouveaux phénotypes aposématiques via les processus évolutifs neutres, conduisant à un haut polymorphisme au niveau de ces populations. L'interaction de ces modes sélectifs nous a permis de démontrer pour la première fois comment la théorie évolutive de Wright (shifting balance theory) permet la diversification adaptative dans un système naturel. Pour conclure, cette étude a permis de mettre en évidence à quel point les systèmes de mimétisme müllérien peuvent être dynamiques. L'alternance spatiale entre les processus évolutifs neutres et la sélection naturelle permet l'émergence de nouveaux phénotypes aposématiques à une échelle locale, ainsi que l'apparition d'une organisation géographique des signaux d'avertissement et des relations de mimétisme müllérien. / The diversification of aposematic signals in Müllerian mimicry systems is a puzzling phenomenon. Although aposematism and mimicry are expected to promote uniformity in warning signals, impressive variations may be observed among populations at relatively small spatial scales. It has been suggested that spatial variation in selective pressures caused by predators might be responsible for this phenomenon. In order to test this hypothesis, we studied the transition in the aposematic signals of the mimetic poison-dart frogs of Northern Peru (Dendrobatidae) between two geographical systems characterized by distinct aposematic signals. This was done by combining population genetics and ecological tools. In both systems, Ranitomeya imitator is sympatric with either R. ventrimaculata or R. variabilis. This system is recognized as a rare example in support of the hypothesis for advergence: R. imitator, which is polymorphic, is believed to mimic distinct sympatric monomorphic model species. However, our results do not support the hypothesis for advergence of the aposematic signals by R. imitator. The genetic similarity between the model species suggests that they have diverged more recently than R. imitator populations or that they are still connected by gene flow. These results indicate that these species were misidentified as being different species. As such, the identification of the mimetic species based on phenotypic variability is invalidated in this system, since R. imitator is as variable as R. variabilis/ventrimaculata. Also, our results demonstrate that predation pressure is spatially variable, in both intensity and direction, thus creating a heterogeneous selective landscape. As such, strong and directed stabilizing selective pressures maintain the geographic organisation of aposematic signals and explain phenotypic uniformity and mimetic relationships. Relaxation of these selective pressures enables for the appearance of novel aposematic phenotypes and promotes high phenotypic variability via neutral evolutionary processes. The interaction between these selective regimes has enabled us to demonstrate, and this for the first time, how the Wright’s shifting balance theory of evolution may promote adaptive diversification in a natural system. In conclusion, this study highlights just how dynamic Müllerian mimicry systems can be. The interplay between neutral evolutionary processes and natural selection enables for the predominance of novel aposematic phenotypes at a local scale, and the geographical organisation of warning signals and Müllerian relationships.

Neophobia and exploratory behaviour are two processes applied in great measure in birds' reactions towards novel stimuli. The specific demonstration of these two processes may differ between different species of birds as well as within them. We compared neophobia and exploratory behaviour in two species of tits (Paridae). Adult Great tits (Parus major) and Blue tits (Cyanistes caeruleus) did not differ neither in exploring novel environment and novel object nor in neophobia towards novel object near food. We have found great differences between juveniles of these two species. Juvenile Blue tits were more neophobic towards both novel objects. Age, sex and personality affected some differences within tested species. We tested whether there exist any differences in reactions towards novel food between and within species. We used red painted mealworm (larvae of Tenebrio molitor), house cricket (Acheta domestica) and aposematic bug (Pyrrhocoris apterus) as novel food. Adult wild-caught tits with plentiful experience with various feeds did not differ in reaction towards these types of novel food. In contrast hand-reared juvenile tits differed quite a lot. Juvenile Blue tits were more neophobic than juvenile Great tits towards all three types of novel food. We found dieraty conservatism, phenomenon...

Flamboyant colors are widespread throughout the animal kingdom. While many of these traits arise through sexual selection, bright coloration can also evolve through natural selection. Many aposematic species, for example, use conspicuous warning coloration to communicate their noxiousness to predators. Recent research suggests these signals can also function in the context of mate choice. Studies of warning color evolution can therefore provide new insights into how the interplay of natural and sexual selection impact the trajectory of conspicuous signal evolution. For my dissertation, I investigated the potential for male-male competition to impact the warning color evolution of a species of poison frog. I focused my work on an exceptionally bright and toxic population of the strawberry poison frog (Oophaga pumilio) where males are brighter than females, a classic signature of sexual selection. In Chapter 1, I used theoretical models of predator and frog visual systems to determine which can see the variation in bright warning coloration within this population. I found that birds, the presumed major predator, likely cannot see this variation, indicating that sexual selection can work under the radar of predators in this species. In Chapter 2, I tested the aggressive responses of males using a two-way choice paradigm that manipulated the perceived brightness of stimulus males. I found that males directed more of their behaviors to bright stimulus frogs, and brighter focal frogs more readily approached stimuli and directed more of their attention to the brighter rival. In Chapter 3, I tested the outcomes of dyadic interactions between males of varying brightness and observed male reactions to simulated intruders in their territories. I found that brighter males initiated aggressive interactions with rivals more readily, and brightness asymmetries between males settled interactions in a way that is consistent with classic hypotheses about male sexual signals. In Chapter 4 I sought to describe physiological correlates of male warning color brightness. While male brightness did not co-vary with classic measures of body condition (circulating testosterone and skin carotenoids), it did correlate with toxins sequestered from the diet and thus appears to be a reliable signal of toxicity in this population. / text

La diversification des signaux aposématiques dans un cadre de mimétisme müllérien est un phénomène intrigant. Alors que la théorie relative à l'aposématisme et au mimétisme suggère l'évolution vers un signal aposématique unique, d'impressionnantes variations peuvent être observées entre les populations, et cela à petite échelle spatiale. Il a été supposé que la variation spatiale des pressions de sélection engendrées par différents prédateurs puisse être à l'origine de ce phénomène. Afin de tester cette hypothèse, nous avons étudié la transition entre deux systèmes géographiques caractérisés par des patrons aposématiques distincts chez des grenouilles mimétiques et toxiques du nord du Pérou (Dendrobatidae) en combinant les outils de génétique des populations aux outils écologiques. Dans chacun de ces systèmes, Ranitomeya imitator vit en sympatrie avec R. ventrimaculata ou R. variabilis. Il s'agit du principal exemple empirique suggérant que dans un cadre de mimétisme müllérien, il n'y a pas convergence des signaux aposématiques des deux espèces, mais plutôt convergence unidirectionnelle où R. imitator, étant polymorphe, imite des espèces monomorphes avec lesquelles elle est sympatrique. Premièrement, les résultats réfutent les prémisses qui suggèrent que R. imitator converge vers le signal aposématique d’une autre espèce. La haute similarité génétique entre les espèces modèles suggère qu'elles ont divergé plus récemment que les populations de R. imitator ou qu'elles sont encore connectées par du flux génique. Ces résultats indiquent que ces espèces ont été identifiées à tort comme des espèces différentes. De fait, l'identification de l'espèce imitatrice basée sur la variabilité phénotypique est invalidée dans ce système puisque R. imitator et R. variabilis/ventrimaculata démontrent la même variabilité. Deuxièmement, nos résultats démontrent que la prédation varie spatialement, autant en intensité qu'en direction, créant ainsi un paysage hétérogène de pressions de sélection. Ainsi, de fortes pressions de prédation stabilisatrice permettent le maintien de l'organisation géographique de différents signaux aposématiques et expliquent l'uniformité de ces signaux ainsi que les relations mimétiques. Par contre, le relâchement temporaire des pressions de prédation permet l'apparition de nouveaux phénotypes aposématiques via les processus évolutifs neutres, conduisant à un haut polymorphisme au niveau de ces populations. L'interaction de ces modes sélectifs nous a permis de démontrer pour la première fois comment la théorie évolutive de Wright (shifting balance theory) permet la diversification adaptative dans un système naturel. Pour conclure, cette étude a permis de mettre en évidence à quel point les systèmes de mimétisme müllérien peuvent être dynamiques. L'alternance spatiale entre les processus évolutifs neutres et la sélection naturelle permet l'émergence de nouveaux phénotypes aposématiques à une échelle locale, ainsi que l'apparition d'une organisation géographique des signaux d'avertissement et des relations de mimétisme müllérien. / The diversification of aposematic signals in Müllerian mimicry systems is a puzzling phenomenon. Although aposematism and mimicry are expected to promote uniformity in warning signals, impressive variations may be observed among populations at relatively small spatial scales. It has been suggested that spatial variation in selective pressures caused by predators might be responsible for this phenomenon. In order to test this hypothesis, we studied the transition in the aposematic signals of the mimetic poison-dart frogs of Northern Peru (Dendrobatidae) between two geographical systems characterized by distinct aposematic signals. This was done by combining population genetics and ecological tools. In both systems, Ranitomeya imitator is sympatric with either R. ventrimaculata or R. variabilis. This system is recognized as a rare example in support of the hypothesis for advergence: R. imitator, which is polymorphic, is believed to mimic distinct sympatric monomorphic model species. However, our results do not support the hypothesis for advergence of the aposematic signals by R. imitator. The genetic similarity between the model species suggests that they have diverged more recently than R. imitator populations or that they are still connected by gene flow. These results indicate that these species were misidentified as being different species. As such, the identification of the mimetic species based on phenotypic variability is invalidated in this system, since R. imitator is as variable as R. variabilis/ventrimaculata. Also, our results demonstrate that predation pressure is spatially variable, in both intensity and direction, thus creating a heterogeneous selective landscape. As such, strong and directed stabilizing selective pressures maintain the geographic organisation of aposematic signals and explain phenotypic uniformity and mimetic relationships. Relaxation of these selective pressures enables for the appearance of novel aposematic phenotypes and promotes high phenotypic variability via neutral evolutionary processes. The interaction between these selective regimes has enabled us to demonstrate, and this for the first time, how the Wright’s shifting balance theory of evolution may promote adaptive diversification in a natural system. In conclusion, this study highlights just how dynamic Müllerian mimicry systems can be. The interplay between neutral evolutionary processes and natural selection enables for the predominance of novel aposematic phenotypes at a local scale, and the geographical organisation of warning signals and Müllerian relationships.

By warning signalling prey advertises its unpalatability to the predators. Typical examples are true bugs (Heteroptera) combining optical and chemical signals. The aim of this study was to find out the effectiveness of chemical defence against wild-caught adults of great tits (Parus major) and blue tits (Cyanistes caeruleus) and towards hand-reared juveniles of great tits. The tested prey were adults and larvae of two invasive species of genus Oxycarenus (Heteroptera: Oxycarenidae) (aposematic O. lavaterae, non-aposematic O. hyalinipennis), adults of Horvathiolus superbus (Heteroptera: Lygaeidae) and crickets (Gryllus assimilis) as a control prey. We were focusing on the influence of seed bugs to the initial reaction, the learning process and to the displays of discomfort behaviour in tits. Reactions affected by the tit species, age and sex were compared in adults. Juveniles were divided into two independent experimental groups, one group was offered adults of genus Oxycarenus, the second was offered sunflower (Helianthus sp.) or Digitalis sp. seed fed adults of H. superbus. The first bug offered did not elicit an initial aversive reaction in tits, but birds reacted aversively to the bugs after having further handling experience. All juveniles, contrary to the adult tits, attacked at least one bug...

Personality and individual differences in reactions of the Great tit to aposematic prey were investigated. The aim of this study was to assess differences in personality of forty Great tits and find out possible correlation to the reactions of these birds to aposematic prey, the fifth larval instar of firebug Pyrrhocoris apterus.

Aposematic species have evolved conspicuous warning signals, such as bright colors and striking patterns, to deter predators. Some edible and harmless species take advantage of this deterrent effect by mimicking their appearance. Mimicry is a great example of how natural selection produces remarkable adaptations. However, while some species evolve a very close similarity to their models to effectively avoid attacks, others are successful in doing so despite an incomplete similarity, i.e. imperfect mimicry. In some cases, it is surprising how such a crude disguise can fool predators. Why and how imperfect mimicry can persist has been much discussed and considered as a problem for the theory of natural selection. It is therefore of great interest to understand what makes it possible. Predator psychology is an important factor in the evolution of aposematism and mimicry. In the past decades it has been suggested that certain components of prey appearance are more important to predators than others during prey assessment. We developed this idea by incorporating concepts from associative learning, and presented a new approach to explain imperfect mimicry. Our general hypothesis is that prey traits have different salience to predators. Certain traits are perceived as highly salient and are thus used primarily in the discrimination and generalization of prey, while traits with low salience are overshadowed and not used in the assessment. The salience of a trait can depend on how conspicuous or discriminable it is in the particular context, and can vary due to for example previous predator experience. We tested our ideas with wild blue tits and domestic chickens as predators, and artificial and semi-natural prey stimuli. In paper I we found that the trait that was perceived as most salient (color) was the one used to discriminate and generalize between prey. Mimics of that specific trait were highly avoided, despite differences in the other traits. We also found that salience is relative and context dependent (paper II). In a context where two traits were perceived as similarly salient, mimicry of a single trait offered intermediate protection, while mimicry of both offered high protection. In another context, the traits were perceived differently salient, and mimicry of one trait was enough for high protection. In paper III we tested a proposed scenario for the initiation of mimicry evolution in the edible butterfly mimic Papilio polyxenes asterius to its noxious model Battus philenor. The results showed that a partial similarity with the model in the salient black wing color offered intermediate protection from attacks, despite a general dissimilarity. This thesis investigates the major questions of imperfect mimicry: the initial step of mimicry evolution, the persistence of imperfect mimicry, and variation in mimic-model similarity. We conclude that mimicry evolution can begin in a non-mimetic species that acquires similarity to a model species in a high-salience trait. When multiple traits have similar salience, multi-trait mimicry is needed for higher protection. Mimicry can remain imperfect if the differences are in traits with low salience, and therefore under low or no selection pressure to change. To complete the picture, we showed that predators can have a biased generalization toward a more pronounced version of a salient trait (paper IV). The evolution of aposematism could therefore be explained by gradual enhancement of salient traits. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Accepted. Paper 4: Manuscript.</p>