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- Johansen, Aleksandra I., 1980-
(författare)
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Seasonal change in defensive coloration in a shieldbug
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 2. |
- Olofsson, Martin, 1980-
(författare)
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Antipredator defence in butterflies
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Predation exerts a potent selection mechanism and has resulted in a suite of antipredation adaptations encompassing morphological and behavioral traits in prey. In butterflies, several such traits appear to be directed towards birds which are considered as one of their major predators. In this thesis I have investigated tactics by which adult butterflies may survive close encounters with birds. In paper I, I provide supporting evidence that the small white “comma” on females of the comma butterfly, Polygonia c-album, has a distractive function on blue tits and so reduces the attack risk. In paper II & III, I investigate the antipredator efficiency of sudden wing-flicking in two species, the peacock butterfly, Inachis io, and the European swallowtail, Papilio machaon, when confronted with domestic fowl and great tits, respectively. Peacock butterflies were manipulated to either display visible or painted over eyespots. Interestingly, the birds that confronted peacocks with visible eyespots were more likely to utter antipredator alarm calls, which imply that the eyespots may be perceived as real eyes of a potential predator. On the whole, wing-flicking in both species typically induced evasion in the birds which suggests that the birds became frightened rather than perceiving the butterflies as not profitable to attack for some other reason. Moreover, I use blue tits as predators to investigate the possible function of smaller eyespots of satyrine butterflies in that they serve to divert predator attacks. Evidence suggests that low light conditions accentuated in the UV may enhance the deflective function of marginal eyespots in the woodland brown butterfly, Lopinga achine (paper IV). In paper V, I show that the presence of one marginal eyespot on the speckled wood butterfly, Pararge aegeria, can deflect bird attacks; moreover, when the butterfly is concealed against the background, eyespots can also increase the latency time until bird attack. In conclusion, my thesis underscores that behavioral studies of predators are instrumental to aid our understanding of the adaptive significance of certain behavioral and morphological traits in prey.
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| 3. |
- Vallin, Adrian, 1974-
(författare)
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On the protective value of conspicuous eyespots in Lepidoptera
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Eyespots, circular patterns which resemble the general appearance of the vertebrate eye, are widespread throughout the animal kingdom and are for example, commonly found on the wings of butterflies where they have been proposed to confer protection against predation. However, empirical evidence of the adaptive value of eyespots, as well as knowledge of butterfly behaviour under the threat of predation, is scarce. In Paper I, we subjected three butterfly species to attacks by insect eating birds. Results show that, although being closely related, these three species have developed fundamentally different kinds of anti-predation adaptations. Paper II demonstrates that the conspicuous eyespots, in combination with the wing-flicking of peacock butterflies, Inachis io, provide efficient defence against blue tits, Parus caeruleus. Peacocks appear to be edible to blue tits, thus, this is an example of effective animal defence by bluffing. During winter hibernation however, Paper III suggests that adult peacock butterflies do not survive predation better compared with its close relative the small tortoiseshell, Aglais urticae, a species lacking eyespots. In Paper IV we argue that two edible insect species carrying equally large eyespots are not necessarily equally well protected against bird predation. In this study, a higher frequency of the larger prey, the eyed hawkmoth, Smerinthus ocellatus, were killed compared with the smaller prey, the peacock butterfly. Finally, Paper V shows that birds approach emperor moths, Saturnia pavonia, a species always exposing their eyespots, earlier after the onset of a trial, compared with eyed hawkmoths, a species hiding their eyespots until harassed by a bird. This suggests that large eyespots may catch the attention of a nearby predator and in situations where predators are not intimidated by the display, eyespots may switch from being potentially beneficial to being a costly trait.
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