During our field trip we had to complete a group research project. We worked in groups of three and our group was assigned the topic of cyanogenesis in legumes and mollusc herbivory.
Basically some plants produce two compounds which are keep separately in the leaves but when the leaves are damaged (due to chewing) the compounds (cyanogenic glucosides and linamarase) come together and form cyanide. This cyanide deters further grazing and protects the plant form mollusc herbivory (being eaten by snails).
We began by recording data from three species of legumes (Lotus cytisoides, Lotus ornithopodoides and Medicargo polymorpha) across three locations on the island (meadow, beach and a wayside). We recorded the area ground that the plant covered, the number of snails on the plant and the number of leaves that had been grazed out of the total number of leaves on three randomly selected stems from each plant. We studied ten plants for each species across at each location! This meant we collected samples from 90 plants in total and as you can imagine this took a long time, but it wasn’t as bad as you’d think spending the day walking around the sunny Mallorcan coastline.
From this data we calculated the number of snails per m2 and the proportion of leaves that had been grazed.
We decided to look at another variable alongside cyanogenesis; trichome density. Trichomes are little hairs on the leaves and/or stems of a plant. They help to stop herbivores like snails grazing on the plants. We found that L. cytisoides had the most trichomes and M. plymorpha had the least.
We also collected a sample of ten plants of each species at each location and from these did a chemical analysis using picrate paper of the cyanide levels in the leaves.
Collecting all this data allowed us to statistically analyse the differences between the species. From the initial analysis it looks as though L. cytisoides has the highest trichome density, cyanide levels and the lowest amount of grazing.
At the end of the week we had to present our project to the rest of the group and it was great to hear about all the other projects people had done! It was a really good experience to plan and carry out a project from the beginning, this will also be useful when we come to plan our dissertation projects next year. Now I’ve just got to get on with writing a report about it (which makes up 40% of the marks for the module)!