The role of predator selection on polymorphic aposematic poison frogs

The role of predator selection on polymorphic aposematic poison frogs

Biology letters (2009) Vol. 5, No. 1, 51-54
Brice P. Noonan, Aaron A. Comeault
Department of Biology, University of Mississippi, University

Demonstrations of interactions between diverse selective forces on bright coloration in defended species are rare. Recent work has suggested that not only do the bright colours of Neotropical poison frogs serve to deter predators, but they also play a role in sexual selection, with females preferring males similar to themselves. These studies report an interaction between the selective forces of mate choice and predation. However, evidence demonstrating phenotypic discrimination by potential predators on these polymorphic species is lacking. The possibility remains that visual (avian) predators possess an inherent avoidance of brightly coloured diurnal anurans and purifying selection against novel phenotypes within populations is due solely to non-random mating. Here, we examine the influence of predation on phenotypic variation in a polymorphic species of poison frog, Dendrobates tinctorius. Using clay models, we demonstrate a purifying role for predator selection, as brightly coloured novel forms are more likely to suffer an attack than both local aposematic and cryptic forms. Additionally, local aposematic forms are attacked, though infrequently, indicating ongoing testing/learning and a lack of innate avoidance. These results demonstrate predator-driven phenotypic purification within populations and suggest colour patterns of poison frogs may truly represent a ‘magic trait’.

Keywords: aposematic, selection, Dendrobates, magic trait

Warning displays may function as honest signals of toxicity

Warning displays may function as honest signals of toxicity

Proceedings of Royal Society B (2009) Vol. 276, No. 1658, 871-877
Jonathan D. Blount(1), Michael P. Speed(2), Graeme D. Ruxton(3), Philip A. Stephens(4)
1 Centre for Ecology and Conservation, School of Biosciences, University of Exeter, Cornwall Campus
2 School of Biological Sciences, Bioscience Building, University of Liverpool
3Division of Environmental and Evolutionary Biology, Institute of Biomedical and Life Sciences, University of Glasgow
4 School of Biological and Biomedical Sciences, University of Durham

Many prey species use colourful ‘aposematic’ signalling to advertise the fact that they are toxic. Some recent studies have shown that the brightness of aposematic displays correlates positively with the strength of toxicity, suggesting that aposematic displays are a form of handicap signal, the conspicuousness of which reliably indicates the level of toxicity. The theoretical consensus in the literature is, however, at odds with this finding. It is commonly assumed that the most toxic prey should have less bright advertisements because they have better chances of surviving attacks and can therefore reduce the costs incurred by signalling. Using a novel theoretical model, we show that aposematic signals can indeed function as handicaps. To generate this prediction, we make a key assumption that the expression of bright displays and the storage of anti-predator toxins compete for resources within prey individuals. One shared currency is energy. However, competition for antioxidant molecules, which serve dual roles as pigments and in protecting prey against oxidative stress when they accumulate toxins, provides a specific candidate resource that could explain signal honesty. Thus, contrary to the prevailing theoretical orthodoxy, warning displays may in fact be honest signals of the level of (rather than simply the existence of) toxicity.

Keywords: aposematism, handicap signal, toxicity, trade-off

Role of different colours of aposematic insects in learning, memory and generalization of naïve bird predators

Role of different colours of aposematic insects in learning, memory and generalization of naïve bird predators

Animal Behaviour (2009) Vol. 77, No. 2, 327-336
Kateřina Svádová(a, b), Alice Exnerová(a), Pavel Štys(a), Eva Landová(a), Jan Valenta(c), Anna Fučíková(c) and Radomír Socha(d)
aDepartment of Zoology, Charles University, Praha, Czech Republic
bDepartment of Biology, University Hradec Králové, Czech Republic
cDepartment of Chemical Physics and Optics, Charles University, Praha, Czech Republic
dBiology Center ASCR, Institute of Entomology, České Budějovice, Czech Republic

Among the various properties of visual warning signals, colour seems to be especially important for avian predators. We tested the role of particular colours of an aposematic insect (firebug, Pyrrhocoris apterus; Heteroptera: Pyrrhocoridae) in unlearned avoidance, learning, memory and generalization of a naïve avian predator (great tit, Parus major). The wild type of the firebug is aposematic, red-and-black, and its colour mutants (white, yellow, orange) retain the same black pattern; the bug can be made artificially nonaposematic (painted uniformly brown). Wild-caught great tits avoid the firebug depending on colour, and their reaction to variously coloured prey is a result of avoidance learning and may vary according to their experience. We trained naïve great tits to avoid firebugs of different colours, and then gave some birds a memory test with firebugs of the same colour and other birds a generalization test with firebugs of a different colour. Naïve, hand-reared great tits showed no initial avoidance and attacked firebugs irrespective of colour. They learned to avoid all the colour forms at a similar rate. The generalization was asymmetric: birds that learned to avoid red firebugs did not generalize their experience to yellow or white mutants whereas birds that learned to avoid yellow mutants generalized their experience to red firebugs. The red colour thus represents a more effective signal than the yellow; predation by birds could have played a crucial role in selectively favoured evolutionary transitions from yellow to red coloration in pyrrhocorids.

Keywords: asymmetric generalization; avoidance learning; firebug; great tit; Parus major; peak shift; Pyrrhocoris apterus; signal memorability; warning signal

The protective value of conspicuous signals is not impaired by shape, size, or position asymmetry

The protective value of conspicuous signals is not impaired by shape, size, or position asymmetry

Behavioral Ecology (2009) Vol. 20, No. 1, 96-102
Martin Stevens, Sarah A. Castor-Perry, and Jessica R.F. Price
Department of Zoology, University of Cambridge

Various conspicuous signals in nature promote initial and learned avoidance by predators. It is widely thought that such signals are most effective when highly symmetrical in features such as size and shape, supported by recent laboratory experiments with domestic chicks and artificial prey. However, no study has investigated the effect of asymmetry on conspicuous signals in a natural setting, where viewing distances, angles, predator species, and light conditions vary and where predators encounter prey sequentially rather than simultaneously. We undertook 2 field experiments with artificial gray-scale prey, marked with a pair of white markings presented to wild avian predators, to test the effect of asymmetry on the survival value of conspicuous signals in the field. Experiment 1 had treatments with symmetrical spots or with spots asymmetrical in area between 5 and 50%. All marked
treatments survived better than unmarked controls, but there was no benefit of being symmetrical. Experiment 2 tested the effect of possessing markings asymmetrical for shape or position and any additive effect of these 2 features. Again, symmetry conferred no benefit and targets with markings asymmetrical for position and/or shape survived equally well as those with symmetrical arrangements. These findings indicate that asymmetry in warning signals may not be costly to prey in nature or be of less importance compared with other features of the signal, such as color and overall size.

Keywords: antipredator coloration, aposematism, birds, eyespots, predation, symmetry.

Testing the predatory behaviour of Podarcis sicula (Reptilia: Lacertidae) towards aposematic and non-aposematic preys

Bonacci, Teresa, Gaetano Aloise, Pietro Brandmayr, Tullia Z. Brandmayr and Massimo Capula. 2008. Testing the predatory behaviour of Podarcis sicula (Reptilia: Lacertidae) towards aposematic and non-aposematic preys. Amphibia- Reptilia. 29 (3): 449-453. [t.bonacci@unical.it]

Abstract: Food preferences and the effects of prey chemical repellents in the dietary behaviour of Podarcis sicula were tested using four species of Carabid beetles as prey models. The goal of the study was to assess (i) the ability of P. sicula to recognize insect preys provided with chemical repellents and aposematic colorations under laboratory conditions, and (ii) the importance of chemical signals used by the prey model as antipredatory strategy. Preys used in this study were Brachinus sclopeta and Anchomenus dorsalis (aposematic species) and Amara anthobia and A. aenea (non-aposematic species). Aposematic species are characterized by warning color pattern and by production of chemical repellents, while non-aposematic ones do not. Amara anthobia and A. aenea were attacked with high frequency by P. sicula, Brachinus sclopeta and Anchomenus dorsalis with low frequency. Non-aposematic species were preyed more often than the aposematic ones. Brachinus sclopeta was preyed after low latency, while Amara anthobia and A. aenea after long latency. Non-aposematic species were captured and eaten without difficulty, while when B. sclopeta or A. dorsalis were captured, lizards always tossed their head and then rub the snout on the soil, probably because of the unpalatability of aposematic preys.

Optimal-Foraging Predator Favors Commensalistic Batesian Mimicry

Optimal-Foraging Predator Favors Commensalistic Batesian Mimicry

Atsushi Honma1¤*, Koh-ichi Takakura2, Takayoshi Nishida1

1 Laboratory of Insect Ecology, Graduate School of Agriculture, Kyoto University, Kyoto, Japan, 2 Osaka City Institute of Public Health and Environmental Science, Osaka, Japan

Background

Mimicry, in which one prey species (the Mimic) imitates the aposematic signals of another prey (the Model) to deceive their predators, has attracted the general interest of evolutionary biologists. Predator psychology, especially how the predator learns and forgets, has recently been recognized as an important factor in a predator–prey system. This idea is supported by both theoretical and experimental evidence, but is also the source of a good deal of controversy because of its novel prediction that in a Model/Mimic relationship even a moderately unpalatable Mimic increases the risk of the Model (quasi-Batesian mimicry).

Methodology/Principal Findings

We developed a psychology-based Monte Carlo model simulation of mimicry that incorporates a “Pavlovian” predator that practices an optimal foraging strategy, and examined how various ecological and psychological factors affect the relationships between a Model prey species and its Mimic. The behavior of the predator in our model is consistent with that reported by experimental studies, but our simulation's predictions differed markedly from those of previous models of mimicry because a more abundant Mimic did not increase the predation risk of the Model when alternative prey were abundant. Moreover, a quasi-Batesian relationship emerges only when no or very few alternative prey items were available. Therefore, the availability of alternative prey rather than the precise method of predator learning critically determines the relationship between Model and Mimic. Moreover, the predation risk to the Model and Mimic is determined by the absolute density of the Model rather than by its density relative to that of the Mimic.

Conclusions/Significance

Although these predictions are counterintuitive, they can explain various kinds of data that have been offered in support of competitive theories. Our model results suggest that to understand mimicry in nature it is important to consider the likely presence of alternative prey and the possibility that predation pressure is not constant.

[Article]Being conspicuous and defended: selective benefits for the individual

Being conspicuous and defended: selective benefits for the individual

Christina G. Halpin, John Skelhorn and Candy Rowe

Centre for Behaviour and Evolution, Institute of Neuroscience, Newcastle University, Henry Wellcome Building, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK

Aposematic insects conspicuously advertise their unprofitability to potential predators. However, when these prey initially evolved, they were likely to have been rare and presumably at a greater risk of being detected and killed by naive predators. Both kin and individual selection theories have been used in attempts to explain this apparent paradox, with much of the empirical research supporting kin selection–based theories. Here, we experimentally test how chemical defence levels in prey and avian color biases influence the probability of a rare conspicuous morph having an initial survival advantage. We used newly hatched domestic chicks (Gallus gallus domesticus) foraging on green and purple prey, on a green or purple background, to model the evolutionary scenario of a rare conspicuous morph arising in a population of already defended cryptic prey. Defended prey were produced by spraying them with quinine solution, which the birds readily detect and can learn to avoid. Although attack rates were initially similar for both defended prey types, the chicks only learned to avoid defended prey when they were conspicuous, not when they were cryptic. In addition, defended conspicuous prey were more likely to be rejected on attack than defended cryptic prey, even when first encountered by a predator. These data suggest that there could be a selective advantage for a rare conspicuous morph to arise in a population of cryptic defended prey due to increased avoidance learning and taste-rejection in naive predators. Our findings also suggest that being a non-preferred color and/or highly defended will increase the probability of this evolutionary scenario.

keywords: aposematism, avoidance learning, color bias, predation, receiver psychology, taste-rejection, warning signal.