Laura Bellec: Inside the feeding behavior of a pollinivore

In this new post, Laura Bellec—a new ecological researcher working at the Univ Rennes 1, Rennes, France—discusses her paper: Factors driving the within-plant patterns of resource exploitation in a herbivore—recently shortlisted for the 2022 Haldane Prize for Early Career Researchers.

About the paper

Animals need to find food to survive and grow; however, searching for food is energetically expensive. Thus, animals have evolved strategies that allow them to maximize food intake per unit of time. These so-called ‘foraging strategies’ depend on various characteristics of the food such as its accessibility, its nutritional quality, and the toxins it (might) contain. Therefore, researchers face the question: How can we know which food characteristics drive the foraging behavior of a given animal?

In this study, we tried to decipher the characteristics that influence the feeding behavior of a small pollinivorous beetle called… the pollen beetle. We did that at a very small scale, namely the inflorescence of a rapeseed plant. Before flowering—when the flower buds are still closed—the pollen beetle pierces the bud wall, called the perianth, to reach the pollen inside the bud. It was already known that pollen beetles prefer to feed from the youngest buds, i.e. the smallest ones, but what explains this preference?

(Left)  “Rapeseed pollen beetles” by Gilles San Martin is licensed under CC BY-SA 2.0
“OSR Pollen Beetle 21” by CropShot is licensed under CC BY-SA 2.0

Since pollen beetles feed from open flowers for the rest of the year, we used the preference for flowers over flower buds to answer this question. From a series of lab experiments on plant organs and artificial substrates, we found that the preference for flowers was related to the direct access to the pollen and its higher nutritional quality. We next tested whether these two characteristics could explain the preference for young buds over older ones when flowers are still closed. To do so, we used a mathematical model to predict how much pollen beetles should favor young buds, given the time needed to pierce the perianth and access the pollen, and the nutritional quality of the pollen. We found that young buds are more profitable than older ones, i.e. they allow maximizing nutrient intake per unit of time even though they contain less pollen than older buds. Moreover, simulations showed how much young buds should be preferred fitted very well with the actual preference of pollen beetles. It is then likely that the foraging strategy of pollen beetles on flower buds aims at maximizing nutrient intake per unit of time.

Our study provides new insights into small-scale foraging patterns and highlights the need to characterize and assess the relative influence of several components of diet quality when deciphering selective pressures driving foraging patterns.

About the research

Homemade set-up for preliminary tests during the lockdown (credit: Laura Bellec)

I started my PhD about three weeks before the first COVID-19 lockdown. What a start! But we didn’t waste any time during these few months at home. My supervisors suggested that I work on the research started by Gaëtan Seimandi-Corda (first co-author) during his PhD before me, and on which they had reached an impasse. In fact, at that time, the different factors considered did not provide a complete picture and understanding of pollen beetle feeding patterns at a small scale.

Feeding tests with pollen beetles and artificial substrates (credit: Laura Bellec)

Since, to be honest, there wasn’t much to do during this period, I read a lot and discovered the field of nutritional ecology and the nutritional geometric framework, and I thought that maybe our solution was there. The influence of nutrient content was not necessarily something we were really studying in the lab at the time—we were more focused on chemical ecology, looking at the influence of metabolites on insect behavior. Since we were on the third renewal of the government lockdown and excited to apply this framework to our study, we thought “why not do some preliminary tests at home?” The plants, insects and all the necessary material were brought back home, after some negotiations with my flatmates, of course. I set up a whole room in our house for my experiments and did my first tests with my flatmates as auxiliary lab technicians.

From these tests, we found out, for the first time, that the nutrient content of the resource has a significant influence on resource selection by the pollen beetle. After the lockdown, and with the precious help of Maxime Hervé (the last co-author), we conducted all these experiments under controlled laboratory conditions, analyzed the data, and reproduced the results obtained previously—the direction to take then became much clearer and led to the present study. But it all started in a flat-share’s office!

Pollen beetle (orange arrow) in oilseed rapeseed flower in the field (credit: Laura Bellec)

This was the first research I did during my PhD, and after that we didn’t see things the same way and realized the importance of considering host plant selection through several prisms. The development of artificial substrates to test the effects of both nutrients and metabolites has made it much more accessible to study these factors, their interactions, and their relative contributions to explain insect feeding behavior. I am currently in the last month of my PhD, where I am trying to unravel the determinants of host plant selection by pollen beetles at different scales (i.e. within the plant, between plant genotypes and species, and between plant families) using nutritional and chemical ecology with quantitative genetics.

About the author

Sampling flower buds and dissection of the different organs on an oilseed rape inflorescence (credit: Arnaud Gougeon)

My story with ecology began very early in a small agricultural high school lost in the wilderness where I was a boarder and where the science program included ecology lessons. The theory in class, combined with the outings in the wild, convinced me of the attraction I already had for nature and the understanding of its functioning. After that, I moved to the most beautiful region of France, Brittany, where I completed a bachelor’s degree in organismal biology. I continued my studies with a master’s degree in functional behavioral and evolutionary ecology. I then started a PhD in collaboration between the University of Rennes 1 and Innolea (a plant genetics research company), where I am now working on the mechanisms of host plant selection by a pollinivorous beetle, under the supervision of three brilliant researchers, Anne-Marie Cortesero, Maxime Hervé, and Sébastien Faure.

In my opinion, the best thing about being an ecologist is the fact that it’s such a stimulating job. Having the opportunity to ask questions and try to answer them, while getting paid—what could be better? I also feel fortunate to be an ecologist, especially when I attend conferences and realize the diversity of fields of study that this area encompasses—a real treat for the curious.

My best piece of advice to other ECRs is to take your head out of your research field, try to step back from what you are doing, attend conferences, read articles, and have discussions about your PhD with your colleagues and friends. The solutions you are looking for may not be so far away.

Laura in a rugby scrum (credit: Jérôme Pagès)

During my spare time, I play rugby. It allows me to clear my mind after a busy day. We can see a certain link between rugby and ecology. In rugby, the scrum consists of eight players packing together and trying to gain ground, with each player in the scrum having a specific function contributing to its overall progress—the success of the scrum cannot be attributed to one individual player alone. It is when you look at it as a whole and see the connections between the players that you understand why it is so stable and progresses so well. I think that in science, this is also often the case—by only looking through one prism, it is difficult to understand biological phenomena. It is only by stepping back and considering each component and its relative contribution that we can understand the overall function of something.

Enjoyed the blogpost? Read the research here!

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s