The mollusc Littorina saxatillis is a snail species that is found on the shores around Iceland. There are usually found on rocks, under the stones. The snails may have different in colours (yellow, black, green, brown and etc). On Kópavogur shore and Álftanes shore, they change into different colours by adapting themselves to the environment around both shores. The height of the snails may also be varies and the foot opening ratio may also varies.
Around Kópavogur the shore is relatively sheltered, around the shore is flat and sandy. The sand is usually black in colour. Seaweeds can be found around the shore and is green to dark green in colour. There are not too many rocks around the shore, only small rocks that are found around the shore.
In Álftanes, the shore is opened widely and leads directly to the Atlantic Ocean. Big rocks are all around the area. Seaweeds are usually big and have light green or yellow in colour, no sand around the area.
Research Question:
Is the colour of the snails in Kópavogur shore differs from Álftanes shore?
Hypothesis:
In Kópavogur, more snails are dark-green or black because of the seaweeds are commonly dark in colour and the sand around the shore in Kópavogur is black. The snails mostly live under dark seaweed to protect themselves from predators and some may live in dark sand to hide from predators as well. The snails will most likely be black and green in colour.
In Álftanes, more snails are light green in colour which the snails in Kópavogur expected to be black because in Álftanes the snails do not live under the seaweeds instead they may live on huge rocks which are all around the area in Álftanes. Also, the local area differences of the snails may affect the snails’ colours. The low frequency of bright colours on the snail’s shell in Kópavogur is likely to be due to the relative absorption of solar energy of snails’ shell because they mostly live under seaweed and in Álftanes, the snail’s shell will be darker in colour due to sunlight absorption. The snails in Álftanes shore do not live under seaweed, so sunlight absorption will be less, this due to the environmental selection in area effects.
Design:
Controlled variable: two identical plastic cups, random sampling using same method and 17 Snails on each shore
Independent variable: Kópavogur shore and Álftanes shore
Dependent variable: Colours of snails
Data collection:
Materials
- Two plastic cups
- One pair of latex gloves
Method
- Name two cups which will be used to collect the snails on Kópavogur and Álftanes shores.
- Pick the snails randomly around the area (use latex gloves) with approximately 10 steps forward from the shore (starting point), 5 steps on the right and finally 5 steps on the left.
- Redo 2) one more time
- Collect approximately 17 snails
- Kill the snails by pouring ethanol into both cups and let the snails die, wait for the next day
- Clean the snails by water once or twice
- Let the snails dry
- Put them on the paper
- Take a picture of the snails on both shores
Data processing:
In this table shows the statistics, total number, average and standard deviation of both shores Álftanes and Kópavogur.
Percentage % of the snails in Kópavogur
On the pie graphs (below) shows the colour variation of snails in both Álftanes and Kópavogur shore.
Álftanes
Kópavogur
This is the picture of the snails that have been collected in Kópavogur and Álftanes.
Conclusion and Evaluation
Natural selection is largely influent the colours of the snails because the environment that the snails on each shore are living in, for example those that live under the seaweeds and under the sand have darker shells then those live on the rocks. Sexual reproduction promotes variation in colours but if there are only few colours on each shore the snails would not likely change colours from the original colour which means that they cannot have the same colour in different shore because the limitation of natural selection limited their behaviour. Also, when snails live on the shore, environment affects their living condition such as those snails that live under seaweed would not absorb sunlight properly, so they have darker colour that the one that absorb sunlight properly. My hypothesis proves to be true due to environmental effect and sexual reproduction.
We could measure the sizes of the snails and do the T-test if we measure the size of the snails, in this case we could not be able to do that. As the colours are investigated T-test cannot be carried out. Colours have limited on the quality of the data because it cannot be measure probably, instead of measuring the sizes we calculate percentage of the snails on each shores.
In design the dependent variable should be the sizes because we could observe the differences in natural selection though sizes rather than colour. When colours are investigated it has lack accuracy to observe the changes in natural selection and adaptation.
To improve the investigation we have to clean the snails more than two times to see whether the colours have changed or not. Do not use ethanol to kill them because it could affect on the colours of the snails´ shell and it may become white because the use of the chemical.
References:
- Human evolution: An illustrated introduction by Roger Lewin 2005: Modern evolutionary theory.
- IB Biology by Andrew Allott and David Mindorff 2007: Adaptation and Natural Selection.
