Archives Thèses, HDR

Soutiendra publiquement ses travaux de thèse intitulés :

The evolution of supergenes:

insights from mimicry polymorphism in a butterfly

Le jeudi 5 décembre 2019 à 13h
CEFE, Grande Salle de Reunion

(Soutenance en Français)

            Over a century after the first description of a polymorphism controlled by a supergene, these genetic architectures still puzzle biologists. Supergenes are groups of tightly linked loci facilitating the co-segregation of alternative combinations of alleles underlying complex adaptive strategies. Recombination suppression at supergenes is determined by polymorphic chromosomal rearrangements, which allows the coexistence of highly distinct morphs without the formation of poorly adapted recombinant phenotype. The existence of supergene raises theoretical and empirical questions. Why do these architectures evolve? How is recombination suppressed? How can alternative combinations of alleles be formed? How and why is polymorphism maintained?

The purpose of this thesis is to provide answers to these questions by studying Heliconius numata, a neotropical butterfly displaying a striking diversity of wing color patterns. In this thesis, I show that this polymorphism is encoded by more than ten loci controlling different features of wing patterns. Recombination between these loci is suppressed by three chromosomal inversions in tandem that form a supergene. In addition to the variants controlling wing coloration, I show that these inversions capture many recessive deleterious mutations, which associate with a high mortality in larvae homozygous for the inversions. In addition, inversions at this supergene are known to underlie morphs with a better protection from predators relative to morphs with ancestral arrangements. The antagonistic effects of inversions -low larval survival but good adult protection- maintains them at intermediate frequencies, and therefore explains the polymorphism observed in this taxon. Then, I show that the first derived inversion of the supergene arose in another species, and was introgressed into H. numata c.a. 2.3 million years ago. This resulted in the cluster of two differentiated, non-recombining haplotypes controlling various aspects of wing patterns, and therefore explains how the supergene of H. numata was formed. Finally, I show via a population genetics model that this scenario of supergene formation involving gene flows between species is able to explain the formation of supergenes in many cases. This thesis sheds new light on the conditions for the evolution of supergenes. In a broader context, it highlights mechanisms that play an important role in the evolution of new genomic architecture and in the adaptation of species

Mots clefs : Supergene, inversion, chromosomal rearrangement, polymorphism, balancing selection, introgression

Membre du jury composé de

Tatiana GIRAUD                                 Directrice de recherche, ESE - Orsay
Vincent CASTRIC                               Directeur de recherche, EEP - Lille
Marianne ELIAS                                 Directeur de recherche, ISYEB - Paris
Anna-Sophie FISTON-LAVIER             Maître de conférence, ISEM - Montpellier
Pierrick LABBÉ                                  Professeur, ISEM - Montpellier
Mathieu JORON                                 Directeur de recherche, CEFE - Montpellier