Bertanne Visser was recently appointed FNRS research associate at the Earth and Life Institute, gaining the opportunity to continue her research on lipid synthesis in certain wasps during evolution. It’s a trait which, contrary to what might be believed, has never been lost.
When a living organism absorbs carbohydrates (sugars), a portion is directly used to provide energy. The surplus is transformed into fat reserves: this is the synthesis – or metabolism – of lipids. This trait is widespread in the animal kingdom, including humans. But not all species need lipid synthesis. Example: parasitoid wasps.
These species of wasps have a particular mode of reproduction. They lay their eggs in another insect (a caterpillar, for example). Wasp larvae hatch and feed on the host to develop. It sounds a bit rude but is an effective technique: parasitoid wasps are widespread.
A vanished trait?
‘This way of life and parasitic reproduction should make lipid synthesis superfluous’, explains Bertanne Visser, a lecturer and research associate at the UCLouvain Biodiversity Research Centre and member of Louvain4Evolution. ‘Indeed, if an animal produces fat – from excess carbohydrates – building up fat reserves requires energy. However, this isn’t the wasp’s case: feeding off the host provides all the fat it needs, neither more nor less. So we thought that parasitoid wasps had lost the trait – lipid synthesis – about 200 million years ago.’
However, during her postdoc at UCLouvain, Dr Visser discovered interspecies and intraspecies variations. Some species and individuals of the same species were ‘fat’. This suggests that lipid synthesis had been reactivated. To confirm her hypothesis, she conducted several experiments. ‘We separated the girls from a mother and put them in different environments. In a high fat environment, they don’t need lipid synthesis. On the other hand, if they lack it, they need the trait, because they must be able to generate reserves.’
A genetic ‘switch’
Dr Visser and her colleagues then looked at the insects’ DNA. ‘Normally, when a trait is not used by a species for a long time, the genes that code it mutate so much that they eventually disappear. We discovered that the gene sequence involved in lipid synthesis is indeed present in parasitoid wasp species (and other parasitic insects). The trait hasn’t disappeared during evolution. It’s just that the genes don’t express themselves ... except under certain circumstances. Lipid synthesis is then reactivated. A bit like a switch that comes on when the wasps need it.’ This was confirmed by a computer simulation. ‘We have shown that the switch can stay in the genome for a very long time, even if it’s only activated once or twice over thousands of generations.’
Further research prospects
The expression of a genetic trait is what is called phenotypic plasticity. The phenomenon has been known for a long time, but this is the first time it has been observed in lipid synthesis. It opens up at least four areas for further research:
- How does this plasticity work? At what point in the wasp’s life is the switch turned on?
- Do other parasitoid wasp species have this plasticity?
- In nature, in real conditions, how does it unfold? Does plasticity depend on the time of year, climate, host type, etc.?
- How does lipid synthesis regulate itself?
A fascination for evolution
Over time, Dr Visser hopes to understand how plasticity functions in lipid synthesis in parasitoid wasps, and perhaps also in other animal species. ‘Nature has always fascinated me’, she says. ‘During my biology studies in the Netherlands, I quickly became interested in scientific investigation. For example, during my master's degree, I participated in a research project on the homosexuality of butterflies. The mechanisms of evolution fascinate me. How do different life forms work? How have they adapted and developed until today? There are still so many questions to explore! Evolution is a perfect area to conduct research in!’
A glance at Bertanne Visser's bio
Bertanne Visser is a research associate in the Evolution and Ecophysiology Group at the Earth and Life Institute's Biodiversity Research Centre. She is also a lecturer at UCLouvain. She holds a master's degree in ecological sciences and evolution, earned at the University of Leiden (Netherlands) in 2007, and a PhD, earned at the Free University of Amsterdam in 2012. She has conducted research on the evolution of insects at the University of Florida (USA, 2012), the University of Tours (France, 2013-15) and UCLouvain (since 2016). She has won several awards and scientific scholarships. She is a member of the Royal Dutch Zoological Society Board of Directors. She is also very active in the Peer Community in project, a scientific organisation which aims to create specific communities of researchers who read and recommend free of charge unpublished preliminary manuscripts in their field.