‘It’s like science isn’t enough in itself'

Séverine Fourdrilis, showing her collection of Melarhaphe neritoides
17/05/2019
‘It’s like science isn’t enough in itself'
post by
Siska Van Parys

Tiny snails can tell great stories... When Séverine Fourdrilis started her PhD at our Institute 7 years ago, her plan was to carry out a rather classical genetic study on marine snails. After one year however, she discovered something strange was going on with one of the species’ genes. She was fascinated, but to investigate it she would have to turn around her PhD entirely, without knowing where she would end up. She took the risk and went off the beaten track.

Séverine Fourdrilis is a marine biologist and works as a postdoctoral researcher at RBINS. She arrived at the Institute 7 years ago, for a PhD on the distribution and genetic diversity of four marine snail species, called ‘periwinkles’. After an intense periwinkle hunt throughout Europe, she started with the analysis of the mitochondrial DNA (mtDNA) of the first species: Melarhaphe neritoides, a tiny snail living along the rocky coastlines of the Mediterranean Sea and the European Atlantic Ocean. The planktonic larvae of this species are carried around by water currents, which allows genes to be exchanged to the four cardinal points of Europe, all the way up to the Azores!

‘Our software programs just didn’t know
how to handle this amount of variability’

This may sound exciting, but for geneticists this makes them of limited interest (i.e. boring), because they are thought to be genetically homogenous over wide geographic areas. This was exactly what Séverine expected to see when analysing their mtDNA. But the results were completely the opposite: nearly every individual snail carried a different genetic variant! As such M. neritoides appeared to have one of the most diverse mtDNA among all marine gastropods for which such data are available, so variable that it is called hyperdiverse mtDNA.

To Risk, Or Not to Risk?

‘At first this was actually a big problem for us’, says Séverine. ‘Our software programs just didn’t know how to handle this amount of variability. We were stuck. But at the same time, I was fascinated. Where does this hyperdiversity come from? Why is it so different than in many other organisms? How did this arise? Did our results suggest that, despite their long-lived planktonic larval stage, larvae do not travel and do not carry their mtDNA to other populations? A puzzling question, since scientific literature qualifies this snail as an excellent disperser showing a high degree of genetic similarity among geographic populations.

However, investigating this did not at all fit in the timeframe of my PhD. I had another type of DNA to sequence and three more species to analyse. I was one year far in the PhD process and the schedule of the next three years was already made. People around me warned me it’s a risky thing to do; you have this well-designed project with clear objectives that have to be met, while when you start to explore something unknown you have no idea where you will end up.’ 

‘People around me warned me
I was taking a big risk’

Her supervisor Thierry Backeljau helped Séverine solve this dilemma. He was intrigued by the observation and convinced that the right thing to do was to explore it. He supported her to take the risk and follow her curiosity. And that’s what she did. She gathered all her courage, let go of the original plan and accepted the challenge. She went back into the lab for another year and surveyed over more than 400 extra snails, not sure if it was going to lead anywhere. But it did.

An Extremely High Mutation Rate

‘So, we were facing the challenging paradox of a snail species having larvae capable of long-distance dispersion, but nevertheless showing no mtDNA variants occurring in more than one individual or population. However, we found out that the alleged paradox was deceiving: the lack of shared mtDNA variants among populations was not caused by a lack of larval exchange, but by an extremely high mutation rate of the mtDNA!’ In other words, they do exchange larvae, but the homogenising effect of this exchange on the mtDNA pales into insignificance compared to the variation that arises through mutations.

A very intriguing phenomenon, that could be more widespread than we think. It is estimated that hypervariable DNA exists in about 43% (!) of all animal species and has been observed in very different groups: invertebrates, insects, birds, even in mammals. Until now, however, this was nothing more than an observation: no one tried to unravel the mechanism behind it. ‘I think that many people who observe this put it aside because their research objectives are focused on something else. We really went deeper to try to explain this. Further research should point out if also in other species this variability is due to an extremely high mutation rate, but I think it is much more common than we think. This snail may be the first to put attention on this phenomenon. And this is not all. The tiny boring snail revealed another phenomenon, so far only found in one worm and one fruit fly: the influence of natural selection on some parts of mtDNA that were thought to be neutral, so not susceptible for selection.’

No Time to Fail

This work teaches us many valuable lessons. First, it warns against too hasty conclusions about the presence or absence of genetic exchange among populations. It also shows that very common organisms, often considered as boring, may nevertheless yield very surprising and valuable results.

‘Nowadays there’s not much room for
exploring the unplanned, and risking failure’

But the most important lesson of it all is that sometimes it’s worth the risk to follow your curiosity. ‘When you observe something you can’t explain, you can choose to explore it, instead of ignoring it because it doesn’t fit in the plan. After all, isn’t that what science is - or should be - all about? Nowadays there’s not much room for exploring the unplanned and risking failure. We go more and more towards this productive, efficient world, where you must guarantee that you will have conclusive results at the end and don’t have any time to fail. If you want to get funding for your project, they almost ask you results already. You basically have to say, “we are almost sure that we will find this”. Or you must show there’s some kind of economic interest. It’s like science is not enough in itself.’

When asked if she’s proud of her work, Séverine answers: ‘After I went off the beaten track (my whole PhD basically!) I was always doubting. I did see the value of it but could not face the stressful uncertainty, “what if I eventually don’t provide an explanation of the phenomenon in a timely fashion?”. But in the end, we turned the initial problem into something nice. That is a relief, and only when you are relieved you can be proud of the work. After all is said and done, I realise it was an extraordinary scientific journey.’

 

Séverine is first author of three scientific papers regarding this topic, in three scientific journals: PeerJ – Life & Environment, Nature’s ‘Scientific Reports’ and BMC Evolutionary Biology. They are all Open Access.

 

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