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