Claire Mérot

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Research interest

Every day, whether I go walking in a garden or have a look at my plate, I am impressed by the incredible diversity of life on Earth. Biological diversity, recently named"Biodiversity", is a multiplicity of species but also shapes, colours, characters, and at a larger scale, a large variety of environments, with their own community of species.

My research interests are part of this general aim to understand the evolution of biodiversity on several timescales. Actual diversity is the result of millions of years of evolution... And it can change and be altered very suddenly, for example due to human activities. My first research projects allowed me to study ecosystem diversity and their conservation in face of global change but also life-history in intra-specific systems. I am now interested in the evolutionary forces that shape the diversity of species and phenotypes.

During my PhD, I have studied the process of "speciation", the evolution of distinct species. More specifically, I asked how the balance between gene flow and reproductive isolation, the balance between divergent selection and stabilizing forces trigger the divergence between taxa. My current post-doc project focus on polymorphism , asking how chromosomal inversion contribute to the maintenance of intra-specific diversity and to adaptation.

I think that studying this kind of process requires the integration of several approaches and I like working with a combination of different methods: observations and experimentation in the field, molecular biology, genomics, lab analysis and modelling.

Current post-doc project (University Laval, Québec)

The role of chromosomal inversion in adaptation to heterogenous environments in seaweed flies

Species evolution and adaptation has been suggested to be enhanced by certain genomic structures. One of these are inversions, where a segment of the chromosome breaks, is reversed and then re-inserted. The most compelling aspects of inversions is reduced recombination due to a decrease in synapsis formation in heterozygotes. As a result, inversions accumulate more variation than collinear regions and show intriguing patterns, such as varying in frequency along ecological clines, being involved in hybrid vigour, and harbouring an overabundance of loci involved in adaptation, population divergence and speciation.

My project addresses the role of inversions in adaptation by means of a multi-layer integrative approach using the seaweed fly Coelopa frigida as a model species. By studying the population ecology, genomics and inversion frequencies in natural populations along a latitudinal cline, I am assessing the association between inversions and adaptation to heterogeneous environments, while accounting for demographic history. Then, using laboratory experiments, I am explicitely testing fitness and investigating functionally the genetic basis of local adaptation.

My aim is to shed light on the modalities by which chromosomic inversions contribute to adaptation in a non-model species and the selective forces and genetic mechanisms underlying the evolution of such structures.

Past project (MNHN, Paris): Speciation in mimetic butterflies

PhD: Speciation in Heliconius butterflies: The balance between mimicry convergence and ecological divergence.

Recent radiations, such as the mimetic radiation of Heliconius butterflies in the Neotropics, offer an excellent example to address the evolutionary processes involved in speciation with gene flow. During my thesis, I explored an interesting situation in the Heliconius clade: two sibling species that are co-mimics of each other, sharing a similar wing colour pattern. This offers the possibility to study the limits of the classical model of speciation associated with shifts in wing pattern, usually described in this group. Colour pattern divergence indeed triggers strong reproductive isolation through disruptive natural selection for Müllerian mimicry and through sexual selection and assortative mating. I investigated how Müllerian mimicry affects species differentiation and reproductive isolation.

Specifically, I explored genetic divergence, coexistence, mimetic relationship and isolating barriers between the co-mimics H. timareta thelxinoe and H. melpomene amaryllis. I showed that the two species maintain consistent genetic and phenotypic divergence while hybridizing at low frequency. They display close resemblance in colour pattern, whose accuracy is affected by the composition of local mimetic community. Through controlled crosses, I showed that hybrids are intermediate in wing pattern and shape, suggesting that predation does not trigger strong post-mating isolation. However, behavioural sexual pre-mating isolation is high due to mate choice, likely relying on chemical cues.

Overall, my results confirmed that Müllerian mimicry between closely-related species likely enhances gene flow and acts against species differentiation. Nevertheless, this effect is balanced by the multidimensionality of isolating barriers, triggered by other ecological factors driving divergence.

For more details, I invit you to contact me or to consult my communications and publications

Post-Doc: Genetic basis of chemical signals and wing morphology.

During my PhD, I mainly studied the phenotypic and ecological aspects of reproductive isolation between the two mimetic sister-species Heliconius timareta and H. melpomene . My short post-doc projet proposed to deepen this topic by adressing the genetic basis of reproductive isolation. To do so, I took advantage of the experimental crosses performed in Peru during my PhD and the analyses of hybrid phenotype. With RAD-seq analyses in collaboration with Cambridge university, we are building a genetic mapping of traits of interest (wing morphology and chemical signature).

We seek to locate those loci within a mosaic genome, mixing pieces with high divergence and pieces introgressed between the two species, in order to understand how ecological and genomic factors contributed to speciation with gene flow and the exceptional diversity of Heliconius taxa.

Undergraduate projects

Plants/pollinators webs in urban environment

How do mutualistic interactions of pollinisation build up in urban environment such as parks or uncultivate lands? How are they influenced by the caracteristics of the city ?

During a short internship at Bioemco lab, I was involved in identifying pollinator insects from the summer field season and in the analyses of data about diversity of plant/pollinator interactions. Another part of my work consisted in elaborating experimental protocoles for a new project in the same theme.

Vegetal communities of Kerguelen islans in a context of biological invasions and climatic changes.

For a few years, Kerguelen Archipelago has known an evolution towards a dryer climate and a deep modification of vegetal communities due to the introduction of alien species. It is generally difficult to evaluate how those rapid changes impact natural communities. In Kerguelen, a very detailled monitoring of vegetation has been done between 1992/97 and 2009 on five islands by Jean-Louis Chapuis's team.

During my master's internship, I did a preliminary global analyses of those data to evaluate the impact of introduced species (plants and herbivores) and the influence of recent climate changes on vegetal communities.

Sex change in two species of gastropods (Crepidula): effect of food and perceived mortality

Most species of Crepidula change sex during their life. Young individuals are first males and, at a specific moment (or size), they turn irreversibly into females. Moment and size at sex change are highly influenced by close environment, especially by conspecific sex. The goal of my project was to investigate other factors that might influences reproductive strategies, such as threat due to food disponibility or predators presence.

This project has been realized for my first year or master at Rachel Collin's lab(STRI), in Panama. .

For more details, you can have a look at the published results.

Wing color variation in Calopteryx and their role in specific recognition or sexual selection

Calopteryx splendens and Calopteryx virgo are two species of damselflies, living around running water in Europe. The most striking phenotypic difference between those sister-species is wing color. This trait is involved in sexual recognition and sexual selection.

During Summer 2008, I participated, as a field assisstant to projects lead by Maren Wellenreuther on those damselflies in Sweden and Finland (University of Lund). We conducted mate choice experiments in the field to study inter-specific discrimination between C. virgo and C. splendens and discrimination against migrants in C. splendens. You will find more details on Maren's project on her website.

As a specific project for my internship, I focused on wing melanisation by measuring reflectance of wings from various populations from Finland and Sweden. We aimed to quantify color variability for the two species and to relate that with behavioural results and latitude of origin.