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Seasonal change in defensive coloration in a shieldbug
Stockholm University, Faculty of Science, Department of Zoology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Protective coloration such as aposematism and crypsis occurs in many insects but only a few species alter their defensive strategy during the same instar. We hypothesize the adult shield bug Graphosoma lineatum with an alternating black and non-melanised longitudinal striation exhibit such a change in defensive coloration. In Sweden, the non-melanised stripes of the pre-hibernation G. lineatum are pale brown and cryptic but they change during hibernation to red and aposematic. We have tested the adaptive functions of coloration of the two G. lineatum forms against bird predators. In Paper I we used great tits as predators and measured detection time of the two forms against a background of dry grass and plants, simulating late-summer conditions. We found that the birds took longer time to find the pale than the red form. Thus, the pale form of G. lineatum is more cryptic in a dry environment than the red form. In Paper II and III we used naïve predators and measured attack rate/latency on red and pale adults and fifth-instar larvae (black and brown) to investigate avoidance and generalisation between the stages. In Paper II domestic chicks initially found the red form most intimidating, but both adult forms are more intimidating than the larva. Moreover, there was a broad generalisation among forms. In Paper III naïve great tits did not find the red form significantly more aversive than the pale adult. Neither the chicks nor the tits showed any difference in the speed of avoidance learning between the two adult colour forms. In Paper IV the shieldbugs themselves were the main focus as we compared activity levels in the different colour forms and found that G. lineatum alters behaviour in accordance to their protective strategy. Thus they were significantly less active during the cryptic phase. Taken together, these experiments suggest that the pale brown adult invests in a cryptic strategy at the cost of reduced protection from aposematism, whereas the red adult benefits from aposematism at the cost of reduced camouflage.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University , 2011. , 26 p.
Keyword [en]
Shield bug, colour change, protective coloration, cryptic, aposematic, behavioural change
National Category
Behavioral Sciences Biology
Research subject
Ethology
Identifiers
URN: urn:nbn:se:su:diva-62466ISBN: 978-91-7447-373-5 (print)OAI: oai:DiVA.org:su-62466DiVA: diva2:442089
Public defence
2011-11-02, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Accepted. Available from: 2011-10-11 Created: 2011-09-20 Last updated: 2011-09-26Bibliographically approved
List of papers
1. Adaptive change in protective coloration in adultstriated shieldbugs Graphosoma lineatum (Heteroptera:Pentatomidae): test of detectability of two colour formsby avian predators
Open this publication in new window or tab >>Adaptive change in protective coloration in adultstriated shieldbugs Graphosoma lineatum (Heteroptera:Pentatomidae): test of detectability of two colour formsby avian predators
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2010 (English)In: Ecological Entomology, ISSN 0307-6946, E-ISSN 1365-2311, Vol. 35, no 5, 602-610 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Antipredatory defence, aposematism, background matching, crypsis, great tit, ontogenetic colour change, Parus major, warning coloration
National Category
Behavioral Sciences Biology
Research subject
Ethology
Identifiers
urn:nbn:se:su:diva-47155 (URN)10.1111/j.1365-2311.2010.01219.x (DOI)
Available from: 2010-11-30 Created: 2010-11-30 Last updated: 2017-12-12Bibliographically approved
2. Change in protective coloration in the striated shieldbug Graphosoma lineatum (Heteroptera: Pentatomidae): predator avoidance and generalization among different  life stages
Open this publication in new window or tab >>Change in protective coloration in the striated shieldbug Graphosoma lineatum (Heteroptera: Pentatomidae): predator avoidance and generalization among different  life stages
2010 (English)In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 24, no 2, 423-432 p.Article in journal (Refereed) Published
Abstract [en]

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, 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 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 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 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 colour polymorphism is discussed

Keyword
Aposematism, Camouflage, Crypsis, Domestic chick, Ontogenetic colour change, Warning coloration
National Category
Biological Sciences Behavioral Sciences Biology
Research subject
Zoological physiology; Ethology
Identifiers
urn:nbn:se:su:diva-29596 (URN)10.1007/s10682-009-9315-3 (DOI)000274109600011 ()
Available from: 2009-09-08 Created: 2009-09-08 Last updated: 2017-12-13Bibliographically approved
3. Anti-Predatory defences in the shieldbug Graphosoma lineatum (Heteroptera: Pentatomidae) differ between life stages and colour forms: an experiment with hand reared great tits (Parus major) as predators
Open this publication in new window or tab >>Anti-Predatory defences in the shieldbug Graphosoma lineatum (Heteroptera: Pentatomidae) differ between life stages and colour forms: an experiment with hand reared great tits (Parus major) as predators
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Crypsis and aposematism are strategies used to avoid predation. Cryptic coloration helps prey to avoid detection and aposematic coloration signals unpalatability to the predator. In the Swedish populations of striated shieldbug Graphosoma lineatum there is a change in coloration and presumably protective strategy that coincides with a change of season and the natural background in the environment. We have compared effectiveness of warning function of colour patterns and chemical defence of three consecutive instars of G. lineatum: the cryptic fifth-instar larvae, the cryptic pale brown and black pre-hibernation adults and the aposematic red and black post-hibernation adults. In experiments with hand reared great tits (Parus major) we investigated the birds’ initial response, avoidance learning and generalisation between forms. We also noted if bugs used their scent glands on attack and if they survived attacks or not. Birds attacked the larvae faster and to a higher extent than the adults, both in naïve birds and after experience, but we found no difference between the adult colour forms in this regard. However, birds generalised asymmetrically between adults and larvae. Previous experience of adults benefited the larvae, but previous experience with larvae increased attack risk on adults and significantly more on the pale than the red adults. Spraying the defensive secretion increased the survival of adults but not the larvae. We conclude that the life stages of G. lineatum differ in defensive strategy against bird predators so that larvae rely on crypsis and the red adults rely mainly on aposematism, whereas the pale adult form seems to do both.

National Category
Behavioral Sciences Biology
Research subject
Ethology
Identifiers
urn:nbn:se:su:diva-62461 (URN)
Projects
Seasonal change in defensive coloration in a shieldbug
Available from: 2011-09-20 Created: 2011-09-20 Last updated: 2014-10-28Bibliographically approved
4. Motion level in Graphosoma lineatum coincides with ontogenetic change in defensive coloration
Open this publication in new window or tab >>Motion level in Graphosoma lineatum coincides with ontogenetic change in defensive coloration
(English)In: Entomologia Experimentalis et Applicata, ISSN 0013-8703, E-ISSN 1570-7458Article in journal (Refereed) Accepted
Abstract [en]

Crypsis and aposematism are two different approaches to predation avoidance. Theoretically, the chosen strategy depends on the prevailing possibilities and constraints to the animal. Consequently, insects often change strategy between life stages, but a switch in strategy within a life stage is quite uncommon. In the Swedish shieldbug, Graphosoma lineatum L. (Heteroptera: Pentatomidae), there is a colour change from the pre-hibernating to the post-hibernating adults that alters their protective strategy from effective crypsis to aposematism, although both stages are distasteful to predators. The change in colour occurs as there is a shift of seasons, which alters the environmental background. Here we investigate if there is a change in behaviour in G. lineatum connected to the change in coloration and protective strategy. We therefore measured the motion levels in the two different colour forms of G. lineatum, both in the field and in a more controlled laboratory set up. Our result clearly shows that there is a change in behaviour connected to the change in colour. Thus, we found that the cryptic pre-hibernation form has a significantly lower motion level than the aposematic post-hibernation form, which is in line with the expectation from the fact that motion disrupts crypsis, but not aposematism. 

Keyword
shield bug, colour change, protective coloration, cryptic, aposematic, behavioural change, activity, Heteroptera, Pentatomidae, Apiaceae
National Category
Behavioral Sciences Biology
Research subject
Ethology
Identifiers
urn:nbn:se:su:diva-62463 (URN)
Projects
Seasonal change in defensive coloration in a shieldbug
Available from: 2011-09-20 Created: 2011-09-20 Last updated: 2017-12-08Bibliographically approved

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