Dissertation focus: Chris Hatcher on Darwin’s “most wonderful plants in the world”

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I thought I would write this blog in way that will hopefully interest you in carnivorous plants as well as giving an insight into some tips and experiences from my dissertation.

‘I care more for Drosera than the origin of species … it is a wonderful plant, or rather a most sagacious animal. I will stick up for Drosera to the day of my death.’ Darwin in a letter to Asa Gray

If this claim doesn’t intrigue, or at least convince you of Darwin’s obsession with carnivorous plants, nothing will. It also shows his remarkable foresight into ecology. Describing a carnivorous plant as “sagacious” (wise) identifies that these plants are not passive, they are finely tuned, actively foraging for prey to acquire nutrients.

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Darwin carried out numerous experiments across carnivorous plant taxa presented in his book Insectivorous Plants. This provided the footing for the next 150 years of research focusing on the main steps of plant carnivory; how they attract, trap and digest prey and the benefit this holds. However many untested questions remain. Though the mechanisms of trapping are widely known, the evolutionary ecology is much less understood. Even less so in the development from seedling to maturity…

This is where I come into the story. For my dissertation, I set out to see whether Venus flytraps are carnivorous throughout their life i.e. do seedlings also trap prey to acquire nutrients for growth?

I began devising a way of doing this in my second year of Biology at the University of Gloucestershire. With the help of Prof Adam Hart, I had a good idea of what I was going to be doing before I left for the summer. The hardest part was getting my hands on some seedlings (actually the hardest part was getting my hands on some seedlings without ripping fragile roots off, tearing leaves or accidentally pulling off the trap while moving them – this is why the initial sample size is always much bigger than the minimum required!). I already had two mature Venus flytraps and so I set about pollinating these, and then planting the seeds. Once enough were germinating at the same time I was able to transplant them into their own cells and begin the experiment.

Planning this before the end of Second Year had many benefits to the final product. Not only did it mean I didn’t have to rush around during Third Year planning and implementing, but it also meant I could use the summer as my growth period.

To confirm Venus fly traps require prey for growth at seedling stage I essentially split the plants into those that could have prey, and those where prey was absent. To do this I sterilised all the peat moss (to rule out soil as a confounding factor), and then reintroduced the most common arthropods I could find in soil around the Uni to the appropriate group. This turned out to be mostly springtails and so I only reintroduced them to the plants (this was a challenge in itself, consider catching hundreds of jumping arthropods that are less than 5mm in length. Then do all this again when you move them into the plant tanks so you know how many have been placed in the tanks to standardise across tanks). Then after four months I compared the changes in plant size. I recorded as many variables as I could, coming in to the lab every morning and quickly getting into a routine. I measured abiotic variables such as humidity, temperature (I regulated the minimum temperature so that the plants would not go into dormancy) and light/dark length. I also rotated the plants position in the lab every day as well as turning them on their “fixed point”. Other variables measured were things like trap number, leaf number (different to trap number because of cotyledons), how many leaves closed and where on the plant so I could tell how long the trap was closed for and trap size. To be honest I wasn’t sure how much of these data I would need but figured it’s much better to have data and not need it.

After statistical analysis, I empirically confirmed that Venus flytrap seedlings were growing at a faster rate when there was prey available. Though size increased, the number of leaves on each plant was not significantly different.

These were the findings I used in my dissertation and after receiving my degree, Adam suggested we go ahead and try to publish the findings. It was at this point that the extra data I had been collecting really came in handy. When reviewers’ comments came in asking for extra information in a table, I was able to quickly turn the paper around with the desired changes. One piece of advice I would give to anyone doing an experiment is to justify and record everything you do. An example of this paying dividends is where one reviewer comment highlighted that pH of the soil was outside the range of natural habitat recorded in a paper some years ago. Fortunately I had tested the pH of the soil at the time of the experiment and it was in line with another paper giving optimum pH values for fly trap culture. This allowed me to defend my experimental setup with published material.

If you are still with me at this point hopefully I have planted a seed of interest in your minds for these plants. “Wonderful” or not, these plants provide a unique way to study all kinds of disciplines, and for me are remarkable.

More information on the findings and implications of my research can be found in the published paper here:

Chris Hatcher, B.Sc. (Hons) Biology 2012

(Chris went on to study an MSc in Evolutionary & Behavioural Ecology at the University of Exeter in Cornwall, and is now in the hunt for a PhD position)

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