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2013-09-25 - Travail avec promoteur/Doctorat - Français - 338 page(s)

Lecocq Thomas , "Différenciation phylogéographique des traits reproducteurs et spéciation chez les bourdons d’Europe", Rasmont Pierre (p) , 2009-10-01, soutenue le 2013-09-25

  • Edition : UMONS (Université de Mons)
  • Codes CREF : Evolution des espèces (DI3127), Sciences exactes et naturelles (DI1000)
  • Jury : Eeckhaut Igor (p) , Mardulyn P., Michez Denis , Frérot Brigitte, de Jonghe R.
  • Unités de recherche UMONS : Zoologie (S869)
  • Instituts UMONS : Institut des Biosciences (Biosciences)

Abstract(s) :

(Anglais) The meeting between mates is one of the most important steps for the reproduction. The individuals localize, recognize, and select their sexual partners through a courtship behavior that involves reproductive traits (e.g. feathers, mating call or chemical secretions). The reproductive traits have a key role in the pre-mating recognition and in the maintenance of reproductive isolation. The evolution of reproductive traits is shaped (i) by intraspecific interactions to maximize encounter rates among conspecific mates (sexual selection), and (ii) by interspecific interactions to maintain isolation barriers and decrease the likelihood of hybridization events among syntopic closed related species, and to minimize predation. Beyond these selective pressures, eco-climatic constraints can also affect the evolution of reproductive traits. Geographic variation in reproductive traits has been observed in several species such as moths, flies, bees, and birds. The geographic variation could be driven by changes in intraspecific selection, interspecific interactions or local adaptation to ecoclimatic constraints across the species area. However, the evolution of sexual recognition signals in geographic framework has received far less attention to date. Now, divergences in reproductive traits act as an important force in promoting prezygotic isolation and speciation. This places a premium to understand the processes that lead to this geographic variation. This research aims to investigate (i) processes and geographic configuration that lead to geographic differentiation of reproductive traits and (ii) consequences of this differentiation on speciation. We broach this topic through 12 species of bumblebees and one important reproductive trait (the male marking secretions). We used phylogenetic and phylogeographic approaches along with comparative analyses of the differentiation patterns and natural variation of male marking secretions on specimens from several populations across their specific area. In the most of model species, our analyses show no geographic differentiation despite variations in eco-climatic features across the species areas. Our results show that the geographic differentiation takes place mainly on islands. The impoverished insular bumblebee fauna does not seem to lead to relaxation of selective pressure on reproductive traits despite the drastic reduction of the species diversity. Our studies suggest that the geographic differentiation of reproductive traits is (i) driven by a persistent lack of gene flow leading to genetic differentiation of genes coding for reproductive traits and (ii) reinforced by female preferences for reproductive traits of local males. This hypothesis does not involve specific insular features. Therefore, the geographic differentiation could be observed between any isolated populations. Our results confirm this hypothesis. The geographic differentiation of reproductive traits is observed between continental populations previously isolated in separated glacial refugia. Our studies show that these geographic differentiations on island or between 8 former glacial refugia can lead to the establishment of a reproductive (pre-zygotic) isolation barrier and to speciation. At the end of this research, new evidences on processes of geographic differentiation of reproductive traits and their consequences have been found. In the case of bumblebee species, the geographic differentiation of reproductive traits does not seem driven by variation in biotopes or in eco-climatic features. In the same way, the reduction of interspecific interactions does not seem to affect the reproductive traits despite the importance of this factors underlined by previous studies. In contrast, the sexual selection appears as the main driving forces in the emergence of new type of reproductive traits in bumblebee species. This sexual selection would reinforce the genetic divergence of genes coding for reproductive traits resulting from rupture of gene flow between allopatric populations. In bumblebee species, geographic differentiation of reproductive traits is mainly recorded in long term isolation. The observed consequences of these differentiation range from simple regional variation (dialects) to the establishment of a reproductive isolation barriers between populations. Therefore, the geographic differentiation of reproductive traits could be one of the most important triggered forces of the current biodiversity.

Identifiants :
  • DOI : 10.13140/2.1.2017.9521