Quantifying colour: my first weeks in labs

Now four weeks into labs, and my last semester at Nottingham, I thought I’d write to explain how my project is going, and what exactly I have been doing so far.
Coming back after Christmas break, I soon submitted my grant proposal- the culmination of all the research I did on Cepaea nemoralis and the plan for my project- and started to put that plan into action.
The aim of my project is to quantitatively measure the colour of Cepaea nemoralis shells found in various locations and altitudes, in order to see whether the existing method of qualitatively scoring colour is reliable, or whether the human perception of colour is limited, and then relate the colour measured to the environmental conditions in which the snail was found. Gathering this information will validate previous results, and help enhance our understanding on the nature of the complex colour polymorphism in this wonderful snail.

I arrived on my first day of labs feeling refreshed and eager to begin. After being shown around, I quickly got to work on preparing my samples, which were still in the form of whole snails that had been frozen shortly after their collection. Pulling the snails from their shells requires a specific technique so that it comes out smoothly and minimises the mess; this job is definitely not for those who become easily squeamish! The snail bodies will be used for genetic experiments that will also be useful in understanding the polymorphism, and so were refrozen soon after. I spent the entire first week doing this, and while it is more social than what follows, I was glad when the last snail had been extracted.

A particularly colourful population of Cepaea nemoralis prepared in the lab.

Once the shells were dried out and labelled, I headed upstairs to a special ‘dark’ room to carry out my measurements. The room is filled with the remnants of previous experiments: jars of honey and protective suits from a bumble-bee study litter the counters. It is small and has no windows as complete darkness is required to get the most accurate reflectance spectra from the equipment, in order to find the precise colour of each shell.
The set-up consists of a light source attached to a probe, which fires a beam of light onto the sample and receives the reflected beam. The light is produced by a deuterium-halogen light source, which covers wavelengths in both the UV and visible light regions as to get the widest spectrum possible. The probe is connected to a spectrometer which measures the wavelengths of the photons sent back, and, via a computer program, produces a spectrum of the reflected wavelengths for each shell. The colour of an object depends on the wavelength of light that it reflects, and so will correspond to a peak on the spectrum. It is important to ensure the probe is at the correct angle and external light sources are minimised to get accurate results. On some shells, the top layer of pigment has been worn away, making the shell appear a different colour to what it would have originally been. This is quite common with shells that would be classified as pink- sometimes the shell is genetically yellow, but this can only be seen on the underside where the shell is protected from harsh environmental conditions; it is here that the measurement is taken.

Equipment used to measure shell colour: the probe focuses a beam of light, produced by a deuterium-halogen light source, down onto the shell, and the reflected beam is analysed by a spectrometer, producing a refelectance spectrum.

The road to getting the equipment to run optimally and producing good spectra has not been smooth, but thankfully all problems have now been resolved. I have also learnt to bring along music or podcasts to listen to while I work, as it helps to get into the routine of repeating the method efficiently without getting bored, especially since the room has to be dark for the majority of the time spent in there. Next, I will have to carry out analysis on my data and write up my findings- something I will worry about when I come to it. For now, though, the goal is to produce spectra for all samples.

The results so far look promising!


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