Thesis
Counting on snails The spiral shapes of sea snails have fascinated Jenny Larsson ever since childhood, growing up on Orust. Now she can call herself a sea snail shell mathematician after defending her thesis on how the spirals can be calculated logarithmically. The sea snail Jenny Larsson researched is called the rough periwinkle Littorina saxatilis, and is found almost everywhere in the Atlantic but also along the entire west coast. The snail is interesting for evolutionary biologists because it is found in two ecotypes, and has adapted to different environments: a slightly smaller one that lives on unprotected beaches and hides in rock crevices when the waves wash in, and a slightly larger one with a thick shell that lives on pebble beaches among seaweed and crabs. But in areas where rocks meet the beach, there are also several intermediate forms. – What biologists are interested in is whether the snails are developing into different species, and what
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role heredity and environment play in that process, says Jenny Larsson. To investigate how the snails differ, she has developed a mathematical model that can describe how tightly the shells’ spirals coil and how the snails grow.
– I have also created a programme where I, based on 2D photos, can construct 3D shapes of the shells and then investigate their hydrodynamic properties, i.e. the power of the wave forces that the different shapes are subjected to at different flow rates and angles. Mathematically, variation in a few parameters is sufficient to explain the diversity in shell shapes that we see in nature. The method can also be easily modified and used to investigate other snail species. It was Jenny Larsson’s overwhelming interest in shapes and geometry that resulted in her studying mathematics. – I obtained both my bachelor’s and master’s degrees from the University of Gothenburg. Then, when I wanted to continue with doctoral studies, I heard about a collaboration on sea snails between the University
