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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
Stockholm University, Faculty of Science, Department of Zoology.
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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: urn:nbn:se:su:diva-62461OAI: oai:DiVA.org:su-62461DiVA: diva2:442011
Projects
Seasonal change in defensive coloration in a shieldbug
Available from: 2011-09-20 Created: 2011-09-20 Last updated: 2014-10-28Bibliographically approved
In thesis
1. Seasonal change in defensive coloration in a shieldbug
Open this publication in new window or tab >>Seasonal change in defensive coloration in a shieldbug
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
Shield bug, colour change, protective coloration, cryptic, aposematic, behavioural change
National Category
Behavioral Sciences Biology
Research subject
Ethology
Identifiers
urn:nbn:se:su:diva-62466 (URN)978-91-7447-373-5 (ISBN)
Public defence
2011-11-02, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
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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

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Johansen, Aleksandra I.Tullberg, Birgitta S.Gamberale-Stille, Gabriella
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