Testing Mimicry in Butterflies
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The experiment will be testing mimicry in butterflies. Mimicry is the similarity between two organisms that evolved to protect a species from its predators. The similarity can be appearance, behaviour, sound or scent. Mimicry can be mutually beneficial for both organisms, or it can be damaging to one of the organisms involved. Batesian mimicry is when a harmless species imitates the warning signals of a harmful species, it is an antipredator adaptation. The wings of the Monarch butterfly are made up of a black, orange and white pattern. They are aposematic in both caterpillar and butterfly form, warning off predators with their bright coloured wings as a warning of their undesirable taste. Cardenolide aglycones is responsible for the undesirable taste of the Monarch butterflies, which the caterpillars ingest while feeding on milkweed. The Viceroy butterfly is distinguishable from the Monarch butterfly from its post median black line on the vein of its hindwing and it is smaller in size. Its defence against predators is mimicry of the Monarch butterfly.
Hypothesis and Predictions
The hypothesis is that mimicry in the butterflies does not have an effect on preference from the birds. Our predictions are that the birds will not choose the model butterfly because of the bright colour of the model butterfly. This means that the birds will more likely choose the mimic butterfly because it is less brightly coloured.
To see which butterfly the birds chooses first and to test mimicry in the viceroy butterfly and to see what effect mimicry has on preference from the birds.
A pilot study was undertook at Treborth Botanical gardens. The study was designed to emulate the mimicry of the monarch butterfly by the viceroy butterfly. This was done using different colour suet pellets. Yellow suet pellets and red suet pellets were used. They both had the same flavour. This was designed so that the birds would be choosing primarily on the colour and not the taste. Five sites of study were chosen. One pile of red suet pellets and one pile of yellow suet pellets were left at each test location. The piles of suet were placed on tree branches and in bird feeders were possible, but some had to be left on the ground. This possibly could corrupt results as ground-based rodents could consume suet pellets and these are not the subject of the experiment. Of the five sites of study four piles of red pellets were fully consumed, compared to only two sites in which the yellow suets were completely consumed. We took this as indication that the birds on site had a preference between the two colours of suet. However, the results may have been corrupted by herbivorous birds and small mammals which may have consumed the suet pellets instead of the target bird species.
Eggs would be collected from the area to be surveyed to ensure successful polymorphs are obtained from both species, and breeding age adult butterflies are not removed from the environment. The eggs would then be reared to adulthood (as only adult viceroys use mimicry). The butterflies would then be freeze-dried to preserve their colour and any unpalatable compounds in their tissues. This would also lower water activity and thus lower the chance of introducing bacteria and other pathogens to bird populations. The area to be surveyed would be divided into quadrats with equal and random treatments across varying habitats (as literature suggests predator density and diversity affects the success of mimicry). Per treatment a Viceroy and a Monarch butterfly would be pinned in close proximity to each other on a tree. First preference of prey would be recorded in the case of a butterfly being eaten by a predator. Predator species could also be recorded to discover if any species (such as different Passeriform species) show a preference for either butterfly.
A chi-squared test is used as data to be generated is frequency count data on which butterfly was chosen first which certifies that the data matches the requirements for a one-way chi-squared test.
After analysing the weaknesses from the pilot study, the method was modified in the hope that it would make the plan stronger. With the issue of other predators, the ability to discount them attacking the butterfly was overcome by monitoring all test species. What was shown in our pilot study that in fact all the brightly colour suet pellet was gone contradicts what we believe should occur but the flaw in the pilot study design may account for that. The expected outcome for this experiment would be that batesian mimicry is shown.
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