Alice Exnerová

Personality matters: individual variation in reactions of naive bird predators to aposematic prey.

Variation in reactions to aposematic prey is common among conspecific individuals of bird predators. It may result from different individual experience but it also exists among naive birds. This variation may possibly be explained by the effect of personality—a complex of correlated, heritable behavioural traits consistent across contexts. In the great tit (Parus major), two extreme personality types have been defined. ‘Fast’ explorers are bold, aggressive and routine-forming; ‘slow’ explorers are shy, non-aggressive and innovative. Influence of personality type on unlearned reaction to aposematic prey, rate of avoidance learning and memory were tested in naive, hand-reared great tits from two opposite lines selected for exploration (slow against fast). The birds were subjected to a sequence of trials in which they were offered aposematic adult firebugs (Pyrrhocoris apterus). Slow birds showed a greater degree of unlearned wariness and learned to avoid the firebugs faster than fast birds. Although birds of both personality types remembered their experience, slow birds were more cautious in the memory test. We conclude that not only different species but also populations of predators that differ in proportions of personality types may have different impacts on survival of aposematic insects under natural conditions.

Nest Defense in Blackbirds Turdus merula: Effect of Predator Distance and Parental Sex

Abstract. Birds frequently use mobbing as a nest defense strategy and the intensity of reaction depends on various factors, e.g., predator species and its distance from the nest. We tested the dynamic risk assessment hypothesis, that is, whether Blackbirds adjust their nest defense to the distance of a predator, Black-billed Magpie Pica pica, from their nest. Responses to a magpie dummy and a Rock Pigeon Columba livia dummy were investigated during the breeding period in an urban environment. The dummies were presented at two different distances, near (1.5 m) and far (6–7 m) from the nest. We also tested the relationship between the sex of a parent and the intensity of mobbing in nest defense. The intensity of mobbing reaction in either parent was highest for the magpie dummy near the nest, although the males showed higher overall intensity than females. When the magpie dummy was far from the nest, the birds preferred hiding in vegetation to mobbing. The highest intensity of vocalization was induced by the magpie dummy near the nest and the lowest by the pigeon dummy. Both parents used “chink” calls more frequently with the magpie dummy near the nest compared to the dummy far from the nest. The “seee” calls were used mostly in response to a distant magpie dummy. The reaction to a pigeon dummy was generally weak, which shows that the birds clearly discriminated between the dummies of the predatory magpie and the harmless pigeon.

Adaptive change in protective coloration in adult striated shieldbugs Graphosoma lineatum (Heteroptera: Pentatomidae): test of detectability of two colour forms by avian predators

1. Protective coloration in insects may be aposematic or cryptic, and some species change defensive strategy between instars. In Sweden, the adult striated shieldbugs Graphosoma lineatum (Heteroptera: Pentatomidae) undergo a seasonal colour change from pale brown and black striation in the pre‐hibernating adults, to red and black striation in the same post‐hibernating individuals. To the human eye the pre‐hibernating adults appear cryptic against the withered late summer vegetation, whereas the red and black post‐hibernating adults appear aposematic. This suggests a possibility of a functional colour change. However, what is cryptic to the human eye is not necessarily cryptic to a potential predator.

Scared by shiny? The value of iridescence in aposematic signalling of the hibiscus harlequin bug

Studies on aposematism have generally focused on the benefits of red or yellow coloration, occasionally in contrast with green or brown, but rarely blue or orange. Furthermore, almost no studies have explicitly studied the utility of iridescent coloration in aposematism. To evaluate the survival benefit of iridescent coloration, we tested the ability of the natural colour extremes of Tectocoris diophthalmus jewelbugs to induce initial avoidance, learned avoidance, discrimination from palatable alternatives and broad generalization against avian predators: naive hand-reared and experienced wild-caught great tits, Parus major. Artificial baits were created by hollowing out bugs and inserting pieces of mealworm. Preference tests presented iridescent and orange baits simultaneously, then birds were divided into training groups and sequentially exposed to palatable black baits alternated with iridescent or orange baits made unpalatable by soaking mealworms in quinine solution. This was followed by simultaneous black/coloured discrimination tests, then a generalization test with both previously experienced and novel baits (all palatable). All groups showed a preference for orange baits over ones with iridescent patches. For wild-caught birds, attack latencies of iridescent and orange training groups were statistically indistinguishable, although only orange caused increased attack latency over the sequence. Hand-reared birds showed no change in attack rate/latency towards iridescent bugs over the sequence. In postlearning discrimination tests, all groups showed equally strong preference for palatable black baits and their unpalatable training baits. In generalization tests, hand-reared birds were most averse towards trained baits, but increased avoidance of iridescent-and-black baits suggests iridescence alone can contribute to aposematism. Wild-caught birds showed strong aversion to iridescent and novel orange-and-black baits regardless of training, suggesting birds may be broadly generalizing experience from local red-and-black aposematic bugs. Results suggest iridescent coloration and patterning can be an effective aposematic signal, especially in the presence of alternative palatable prey and/or other aposematic species.

Nest Defence Intensity in House Sparrows Passer domesticus in Relation to Parental Quality and Brood Value

Abstract. We investigated whether brood value (laying date, brood size, nestling age and condition) and parental quality (condition, male badge size) affect experimentally provoked nest defence in House Sparrows in the Czech Republic. We included the badge size (a melanin-based throat feather patch) because it serves as a signal of social status, age and condition. We presented a stuffed Black-billed Magpie Pica pica to 19 pairs of sparrows. To assess the defence intensity we used the “risk index”, increasing with time spent reacting and riskiness of the reaction (number of approaches and attacks), while declining with increasing distance from the predator. Females did not adjust their nest defence to the brood value and males did so only partially, tending to defend the early broods more intensely, which marginally supports the “value of offspring hypothesis”. The birds did not adjust their nest defence to quality or defence intensity of their partners, thus the “differential allocation hypothesis” was not supported. Male nest defence was more intense than in females and increased with male badge size. As male contribution to nest defence may affect the breeding success, we hypothesize the badge size could be used as a signal of nest defence intensity used by females.

Hydrophilic interaction liquid chromatography with tandem mass spectrometric detection applied for analysis of pteridines in two Graphosoma species (Insecta: Heteroptera).

A new separation method involving hydrophilic interaction chromatography with tandem mass spectrometric detection has been developed for the analysis of pteridines, namely biopterin, isoxanthopterin, leucopterin, neopterin, xanthopterin and erythropterin in the cuticle of heteropteran insect species. Two columns, Atlantis HILIC Silica and ZIC(®)-HILIC were tested for the separation of these pteridines. The effect of organic modifier content, buffer type, concentration and pH in mobile phase on retention and separation behavior of the selected pteridines was studied and the separation mechanism was also investigated. The optimized conditions for the separation of pteridines consisted of ZIC(®)-HILIC column, mobile phase composed of acetonitrile/5mM ammonium acetate, pH 6.80, 85/15 (v/v), flow rate 0.5mL/min and column temperature 30°C. Detection was performed by tandem mass spectrometry operating in electrospray ionization with Agilent Jet Stream technology using the selected reaction monitoring mode. The optimized method provided a linearity range from 0.3 to 5000ng/mL (r>0.9975) and repeatability with relative standard deviation<8.09% for all the studied pteridines. The method was applied to the analysis of pteridines in the cuticle of larvae and three adult color forms of Graphosoma lineatum and one form of Graphosoma semipunctatum (Insecta: Hemiptera: Heteroptera: Pentatomidae). The analysis shows that different forms of Graphosoma species can be characterized by different distribution of individual pteridines, which affects the coloration of various forms. Only isoxanthopterin was found in all the five forms tested.

Through experience to boldness? Deactivation of neophobia towards novel and aposematic prey in three European species of tits (Paridae)

European tits (Paridae) exhibit species-specific levels of initial wariness towards aposematic prey. This wariness may be caused by neophobia, dietary conservatism or innate bias against particular prey traits. We assessed the contribution of these three mechanisms to the behaviour of juvenile tits towards novel palatable prey and novel aposematic prey. We compared levels of initial wariness in great tits (Parus major), blue tits (Cyanistes caeruleus) and coal tits (Periparus ater), and tested how the wariness can be deactivated by experience with a palatable prey. One group of birds was pre-trained to attack familiar naturally coloured mealworms the other one, novel red-painted mealworms. Then all the birds were offered a novel palatable prey of different colour and shape: cricket (Acheta domestica) with blue sticker, and then a novel aposematic firebug (Pyrrhocoris apterus). The three species of tits differed in how the experience with a novel palatable prey affected their behaviour towards another novel prey. Great tits and coal tits from experienced groups significantly decreased their neophobia towards both palatable prey and aposematic prey while blue tits did not change their strongly neophobic reactions. The interspecific differences may be explained by differences in body size, geographic range, and habitat specialisation.

Gregariousness as a defence strategy of moderately defended prey: experiments with Pyrrhocoris apterus and avian predators

Aggregations in insects carry out diverse functions, and gregariousness may also act as an antipredatory strategy, especially when combined with warning signalling. Despite many studies focused on the antipredatory function of gregariousness, there are still aspects needing further investigation: What aspects of predator behaviour are affected by prey gregariousness? Which of the antipredatory effects of aggregations are linked with aposematic coloration, and which will also work for non-aposematic prey? Does gregariousness of an aposematic species affect its mimetic relationships? We have studied these topics in the firebug, Pyrrhocoris apterus (Heteroptera), an aposematic red-and-black true bug with moderate chemical defence. Firebugs alternate between solitary and gregarious lifestyles throughout the year. We used hand-reared great tits (Parus major) as naive predators, and subjected them to avoidance training with either solitarily or gregariously presented firebugs, followed by a memory test with solitary individuals. To test whether effects of gregariousness are specific for the aposematic firebugs, we tested another group of birds with brown-painted firebugs. Our results show that the gregarious lifestyle of the firebug is a part of its antipredatory strategy. Compared to solitary individuals, aggregations benefited in several ways, some exclusive for aposematic firebugs, others working irrespective of coloration. Aggregations induced greater innate wariness, leading to longer attack latencies and more cautious prey handling, including complete attack avoidance in some birds. Despite the fact that the birds mostly attacked only one or two individuals from an aggregation, they needed fewer trials to reach the avoidance-learning criterion than the birds learning to avoid solitary firebugs. Birds’ experience with firebug aggregations reduced the predation risk of subsequently encountered solitary individuals, as the birds hesitated longer before attacking a solitary firebug if their previous aversive experience had been with aggregations rather than with solitary individuals. Predators’ experience with firebug aggregations may compensate for the firebugs’ moderate chemical defence, and as a consequence, gregariousness may change the firebugs’ mimetic relationships with better defended red-and-black true bug species from quasi-Batesian to Mullerian.

The effect of social learning on avoidance of aposematic prey in juvenile great tits ( Parus major )

Social learning plays an important role in acquiring new foraging skills and food preferences in many bird species but its potential role in learning to avoid aposematic prey has never been studied. We tested the effect of social learning on the acquisition of avoidance of aposematic insect prey (firebug Pyrrhocoris apterus; Heteroptera) in juvenile, hand-reared great tits (Parus major). Behaviour towards aposematic prey was compared between two groups of birds: (1) the observers that were, prior to encounter with firebugs, allowed to watch the experienced conspecific demonstrator repeatedly refuse to attack the prey, and (2) the control birds that lacked this opportunity. Observing an experienced demonstrator was not sufficient for learning complete avoidance, because birds from both groups attacked at least the first firebug they had encountered in avoidance training. However, the opportunity to observe the avoidance behaviour of another bird significantly increased the rate of subsequent individual learning of observers in comparison with control birds. Social learning also decreased mortality of firebugs killed by the birds during the avoidance learning. Socially enhanced learning to avoid aposematic prey might be a mechanism important especially for naive juvenile birds learning from their parents, but it could also enhance learning in adults from their more experienced flock mates. Because social learning of avoidance may also lead to decreased mortality of aposematic prey, its effect should be taken into account in scenarios considering evolution and maintenance of prey warning signals.

Capillary electrophoresis of pterin derivatives responsible for the warning coloration of Heteroptera

A new capillary electrophoretic (CE) method has been developed for analysis of 10 selected derivatives of pterin that can occur in the integument (cuticle) of true bugs (Insecta: Hemiptera: Heteroptera), specifically L-sepiapterin, 7,8-dihydroxanthopterin, 6-biopterin, D-neopterin, pterin, isoxanthopterin, leucopterin, xanthopterin, erythropterin and pterin-6-carboxylic acid. Pterin derivatives are responsible for the characteristic warning coloration of some Heteroptera and other insects, signaling noxiousness or unpalatability and are used to discourage potential predators from attacking. Regression analysis defining the parameters significantly affecting CE separation was used to optimize the system (the background electrolyte (BGE) composition, pH value and applied voltage). The optimized separation conditions were as follows: BGE with composition 2 mmol L(-1) the disodium salt of ethylendiamintetraacetic acid, 100 mmol L(-1) tris(hydroxymethyl)aminomethane and 100 mmol L(-1) boric acid, pH 9.0, applied voltage 20 kV and UV detection at 250 nm. Under these conditions, all the 10 studied derivatives of pterin were baseline separated within 22 min. The optimized method was validated from the viewpoint of linearity (R(2)≥0.9980), accuracy (relative error ≤7.90%), precision (for repeatability RSD≤6.65%), detection limit (LOD in the range 0.04-0.99 μg mL(-1)) and limit of quantitation (LOQ in the range 0.13-3.30 μg mL(-1)). The developed method was used for identification and determination of the contents of pterin derivatives in adults of four species of Heteroptera (Eurydema ornata cream color morph, Scantius aegyptius, Pyrrhocoris apterus and Corizus hyoscyami) and their distribution in the individual species was determined.