Evolution; Phylogeny; Entomology; Multivariate statistics; Geometric morphometrics; Invasive species.
I find that one of the greatest beauty of living nature is its endless diversity in forms, coloration or behaviours. With more than a million of species described and hundreds of thousands more yet to be discovered, this diversity is far from being apprehended. Furthermore, most of the known species are only briefly sighted by one or few specimens. Biodiversity is thus a promising field of exploration.
What are the processes that led to the current diversity observed in the nature?
This is the main question I’m working on.
At the species-scale or between different genera, I aim to add knowledge and to help to understand this topic. I’m mostly interested in characterizing the evolution of phenotypes within and between species. Evolution of species, through the progressive accumulation of genetic mutations in different lineages, is one answer to this diversity. Plasticity and the influence of developmental conditions of the specimen is another factor of diversification. Both these processes, genetic information and responses to environmental conditions, are linked through the natural selection. Understanding which part of the phenotype is influenced by each of these factors will help to figure out how the current phenotype diversity was formed.
I mainly work on the quantification of the observed phenotypes in order to assess the influence of these different factors on the variation of characters in organisms. The quantified variation of phenotypes can then be compared and related to environmental, functional or historical data (such as the phylogeny).
Up: Ropalidia nest (A.Perrard). Down: Hover wasp (Stenogastrinae) at rest (Kurt, aka “Orionmystery”)
Insect being the most diverse living group on earth, I oriented my studies to these organisms, especially Hymenoptera (Bees, Ants and Wasps) that display a large range of (cool) shapes, colors and behaviours. My main subject of research, developed during my 3-year Ph.D. started in 2009, is the wing shape quantification by landmark data (Ph.D. Thesis). Wing is a convenient subject for geometric morphometrics because it is a 2D structure involved in flight with homologous venation among individuals. Geometric morphometrics are methods characterizing the shape of objects through their geometry in space. It allows to detect subtle biological variation and to keep a relation between the biological object and its mathematical quantification through the geometric visualization.
The wing venation enables us to identify insects at large scale taxonomy, but when quantified by geometric morphometrics methods, it also discriminate closely related species, populations and even sex or castes. The wing shape marker, easily accessed from specimens in the wild or in natural history collection, could become an useful tool in species recognition and exploration of insect biodiversity.
Three color forms of V. velutina (Q. Rome © MNHN)
Vespa velutina evolution
I’m currently working on the characterization of the wing shape and the color variation across the distribution of the widespread species V. velutina. This species, called the yellow-legged hornet, is distributed across south-east asia and is present on continental areas and archipelago. It displays a wide range of color variations between populations, making it a good subject for phenotypic evolution study.
Main collaborators: ; Michel Baylac and the hymenoptera team of the MNHN: Claire Villemant; Quentin Rome and Franck Muller.
Evolution of the wing shape in Vespine wasps
I’m characterizing the evolution of the wing shape within social wasps of the subfamily Vespinae (Yellowjackets and hornets) to relate the evolution of the phenotype to the phylogeny of this group, assessed by morphological and molecular characters.
Main collaborators: James M. Carpenter; Claire Villemant and Junichi Kojima
Past diversity of Vespidae
(after artwork “touched by his noodly appendage” and hornet picture from J. Haxaire)
Understanding the evolution of a group require to know its past diversity. However, social wasps are rare in the fossil record. Having found several specimens with André Nel in the fossil collection of the Muséum National d’Histoire Naturelle, I’m describing different species of Pollistinae from Eocene.
Main collaborators: André Nel; James M. Carpenter
Evolution of the gastral shapes in Vespidae
Wasps have what we call a “wasp-waist” due to their petiolated gaster. The elongation of the petiole creates a wide variety of body shapes from stout to very elongated gasters. This elongation evolved several times in the family of social wasps (Vespidae) and we are not sure as to why. One of the hypotheses is that it has a role in flight by helping the insect to balance its body. By using CT-scans, I’m quantifying the variation of the shape of the first gastral segments and of the thorax in order to test whether these features are related to a variation of the wing.
Main collaborators: S. Combes
Multivariate phenotypes are analysed in multivariate spaces, in which the variation cannot be expressed by a single value but by a covariance matrix. Covariance matrices define the variation of the data in the multidimensionnal space. But the space formed by all possible covariance matrices is yet not an Euclidean spaces but a complex manifold. Comparison of different covariance matrices involve various methods to apprehend this non-linear dimensionnality. Several non-linear metrics were proposed in order to compare these matrices, however differences in these metrics and their relation to sample size and dimensionnality has yet to be assessed. This is the topic of a current developping project.
Main collaborators: Michel Baylac, Christian Klingenberg