ABSTRACT: Camouflage and warning colouration are two important forms of protective colouration. We have studied the detectability of
two seasonal colourations in the aposematic striated shieldbug, Graphosoma lineatum. The typical colouration of this insect is red and black, which is also the colouration of the reproductive post-hibernation
bugs in our study area in south central Sweden. However, the majority of newly eclosed adults in late summer exhibit a ‘pale’
(light brownish, non-red) and black striation, and these bugs appear quite cryptic to the human eye when sitting on the dried
stems and umbels of their host plants. In experiments using photographs of prey in the late-summer habitat shown on a computer
screen, we compared the time to detection by human subjects of bugs, which had been manipulated to show either of the two
typical seasonal colourations. Time to detection was significantly longer for the pale and black than for the red-and-black
striation in images with the bug photographed at two different distances. This indicates that the pale pre-hibernation striation
may have a cryptic function. In a separate experiment, we tested detectability of striated and non-striated manipulations
of bug pre-hibernation colouration against the late-summer background, and found that time to detection was significantly
longer for the striated bugs. We discuss potential functional explanations for the seasonal ontogenetic colour plasticity
and suggest that the epidermal pale colour in the late summer provides a benefit of increased camouflage.
Behavioral Ecology and Sociobiology 04/2012; 62(9):1389-1396. · 3.18 Impact Factor
ABSTRACT: There are two major forms of protective coloration, camouflage and warning coloration, which often entail different colour There are two major forms of protective coloration, camouflage and warning coloration, which often entail different colour
pattern characteristics. Some species change strategy between or within life stages and one such example is the striated shieldbug, pattern characteristics. Some species change strategy between or within life stages and one such example is the striated shieldbug,
Graphosoma lineatum. The larvae and the pale brownish-and-black striated pre-diapause adults are more cryptic in the late summer environment Graphosoma lineatum. The larvae and the pale brownish-and-black striated pre-diapause adults are more cryptic in the late summer environment
than is the red-and black striation that the adults change to after diapause in spring. Here we investigate if the more cryptic than is the red-and black striation that the adults change to after diapause in spring. Here we investigate if the more cryptic
pre-diapause adult and larval coloration may affect the aposematic function of the coloration as compared to the red adult pre-diapause adult and larval coloration may affect the aposematic function of the coloration as compared to the red adult
form. In a series of trials we presented fifth instar larvae, pale or red adults to shieldbug-naïve domestic chicks, Gallus gallus domesticus, to investigate the birds’ initial wariness, avoidance learning, and generalization between the three prey types. The naïve form. In a series of trials we presented fifth instar larvae, pale or red adults to shieldbug-naïve domestic chicks, Gallus gallus domesticus, to investigate the birds’ initial wariness, avoidance learning, and generalization between the three prey types. The naïve
chicks found the red adults most aversive followed by pale adults, and they found the larvae the least aversive. The birds chicks found the red adults most aversive followed by pale adults, and they found the larvae the least aversive. The birds
did not find the larvae unpalatable and did not learn to avoid them, while they learned to avoid the two adult forms and then did not find the larvae unpalatable and did not learn to avoid them, while they learned to avoid the two adult forms and then
to a similar degree. Birds generalized asymmetrically between life stages, positively from larvae to adults and negatively to a similar degree. Birds generalized asymmetrically between life stages, positively from larvae to adults and negatively
from adults to larvae. We conclude that the lower conspicuousness in the pale forms of G. lineatum may entail a reduced aposematic function, namely a reduced initial wariness in inexperienced birds. The maintenance of the from adults to larvae. We conclude that the lower conspicuousness in the pale forms of G. lineatum may entail a reduced aposematic function, namely a reduced initial wariness in inexperienced birds. The maintenance of the
colour polymorphism is discussed. colour polymorphism is discussed.
Evolutionary Ecology 04/2012; 24(2):423-432. · 2.45 Impact Factor
ABSTRACT: In Batesian mimicry, a harmless prey species imitates the warning coloration of an unpalatable model species. A traditional suggestion is that mimicry evolves in a two-step process, in which a large mutation first achieves approximate similarity to the model, after which smaller changes improve the likeness. However, it is not known which aspects of predator psychology cause the initial mutant to be perceived by predators as being similar to the model, leaving open the question of how the crucial first step of mimicry evolution occurs. Using theoretical evolutionary simulations and reconstruction of examples of mimicry evolution, we show that the evolution of Batesian mimicry can be initiated by a mutation that causes prey to acquire a trait that is used by predators as a feature to categorize potential prey as unsuitable. The theory that species gain entry to mimicry through feature saltation allows us to formulate scenarios of the sequence of events during mimicry evolution and to reconstruct an initial mimetic appearance for important examples of Batesian mimicry. Because feature-based categorization by predators entails a qualitative distinction between nonmimics and passable mimics, the theory can explain the occurrence of imperfect mimicry.
Evolution 03/2012; 66(3):807-17. · 5.15 Impact Factor
ABSTRACT: 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.2. Therefore we tested the effect of coloration in adult G. lineatum on their detectability for avian predators. Great tits (Parus major) were trained to eat sunflower seeds hidden inside the emptied exoskeletons of pale or red G. lineatum. Then the detection time for both colour forms was measured in a dry vegetation environment.3. The birds required a longer time to find the pale form of G. lineatum than the red one. The pale form appears more cryptic on withered late summer vegetation than the red form, not only to the human eye but also to avian predators. The result supports the idea that the adult individuals of G. lineatum undergo a functional change from a cryptic protective coloration to an aposematic one.
Ecological Entomology 09/2010; 35(5):602 - 610. · 2.00 Impact Factor
ABSTRACT: Summary1. The role of food plant and aggregation on the defensive properties of two aposematic sympatrically occurring seed bugs, Tropidothorax leucopterus and Lygaeus equestris (Lygaeinae, Heteroptera), was investigated. Larvae reared on seeds either of their natural host plant Vincetoxicum hirundinaria (Asclepiadaceae) or of sunflower Helianthus annuus were subjected to predation by chicks.2. The two species differ in their dependency on the host for their defence. Lygaeus equestris was better defended on its natural host plant than on the alternative food, as indicated by fewer attacks, lower mortality, and predator avoidance after experience. No such effect of food plant could be found for T. leucopterus, suggesting the existence of alternative defences in this species.3. The number of attacks was lower when host plant-fed larvae of both species were presented in groups.4. The discussion concerns how major components of an aposematic syndrome, such as host plant chemistry, insect colouration, and aggregation, are integrated with other life-history traits to form alternative lifestyles in L. equestris and T. leucopterus.
Ecological Entomology 04/2000; 25(2):220 - 225. · 2.00 Impact Factor
ABSTRACT: An important factor for understanding the evolution of warning coloration in unprofitable prey is the synergistic effect produced
by predator generalisation behaviour. Warning coloration can arise and become stabilised in a population of solitary prey
if more conspicuous prey benefit from a predator's previous interaction with less conspicuous prey. This study investigates
whether domestic chicks (Gallus gallus domesticus) show a biased generalisation among live aposematic prey by using larvae of three species of seed bugs (Heteroptera: Lygaeidae)
that are of similar shape but vary in the amount of red in the coloration. After positive experience of edible brownish prey,
chicks in two reciprocal experiments received negative experience of either a slightly red or a more red distasteful larva.
Attacking birds were then divided into two treatment groups, – one presented with the same prey again, and one presented with
either a less red or a more red larva. Birds with only experience of edible prey showed no difference in attack probability
of the two aposematic prey types. Birds with experience of the less red prey biased their avoidance so that prey with a more
red coloration was avoided to a higher degree, whereas birds with experience of the more red prey avoided prey with the same,
but not less red coloration. Thus, we conclude that bird predators may indeed show a biased generalisation behaviour that
could select for and stabilise an aposematic strategy in solitary prey.
Evolutionary Ecology 08/1999; 13(6):579-589. · 2.45 Impact Factor
ABSTRACT: Aposematic animals are often conspicuous. It has been hypothesized that one function of conspicuousness in such prey is to be detected from afar by potential predators: the ‘detection distance hypothesis’. The hypothesis states that predators are less prone to attack at long detection range because more time is allowed for making the ‘correct’ decision not to attack the unprofitable prey. The detection distance hypothesis has gained some experimental support in that time-limited predators make more mistakes. To investigate effects of prey presentation distance we performed two experiments. First, in experiment 1, we investigated at what distance chicks, Gallus gallus domesticus, could see the difference in colour between aposematic and plain mealworms. Birds chose the correct track in a two-way choice when prey were at 20, 40 and 60 cm distance but not at 80 cm. Second, in experiment 2, fifth-instar larvae of the aposematic bug Lygaeus equestris were presented to experienced chicks at 2, 20 or 60 cm distance. We found no difference in attack probability between distances. However, prey mortality was significantly lower for the shortest presentation distance. In conclusion, we found no support for the hypothesis that aposematic prey benefit from long-range detection; in fact they benefit from short-distance detection. This result, and others, suggests that the conspicuousness of aposematic prey at a distance may simply be a by-product of an efficient signalling function after detection.
Animal Behaviour. 78(1):111-116.
ABSTRACT: Müllerian mimicry is the mutualistic resemblance between two defended species, while Batesian mimicry is the parasitic resemblance between a palatable species (the mimic) and an unpalatable one (the model). These two kinds of mimicry are traditionally seen as extreme ends of a mimicry spectrum. For the range in between, it has been suggested that mimetic relations between unequally defended species could be parasitic, and this phenomenon has been referred to as quasi-Batesian mimicry. Where a mimetic relation is placed along the mimicry spectrum depends on the assumptions made about predator learning. We used a variant of the Rescorla–Wagner learning model for virtual predators to analyse the different possible components of the mimicry spectrum. Our model entails that the rate of associative learning is influenced by variation in the stimuli to be learned. Variable stimuli, that is, unequal defences, can increase the predator learning rate and thus lead to an increased level of mutualism in a mimetic relation. In our analysis, we made use of the concepts of super-Müllerian mimicry, where the benefit of mimicry is even greater than in traditional Müllerian mimicry, and quasi-Müllerian mimicry, where mimicry by a palatable mimic is mutualistic. We suggest that these types of mimicry should be included in the mimicry spectrum along with Müllerian, Batesian and quasi-Batesian mimicry.