Carole Smadja
Evolutionary biology and Behavioural Ecology

Evolution of host plant preference and speciation

Other research projects

My research focuses on speciation, a fundamental evolutionary and biological process responsible for the generation of novel forms and for the maintenance of biodiversity. My objective is to gain insights into the mechanisms of speciation and more specifically to understand the role of selection in the formation of new species. I use a comparative and integrative approach to address these interests by combining phenotypic and genetic analyses of traits involved in reproductive isolation. So far, I have been mainly focusing on mechanisms of divergence-with-gene-flow and on the evolution of behavioural traits responsible for the occurrence of premating isolation among diverging taxa.

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Selection, divergence-with-gene-flow and speciation

Selection has been shown to promote the evolution of reproductive isolation in many situations. In allopatry, speciation can for example occur as a by product of differential regimes of natural or sexual selection among the different environments. However, the role of selection in speciation is even more crucial when populations are diverging in the face of gene flow: theoretical studies of speciation show that only adaptive mechanisms can counter-act the diluting effect of recombination while populations still exchange genes, thus offering a route towards speciation. I study populations experiencing gene flow (hybrid zones; sympatric populations) and try to understand how selective processes can facilitate divergence-with-gene-flow. So far, my work on the house mouse and the pea aphid has led me to address mechanisms of reinforcement between diverging subspecies and of ecological speciation between sympatric host races, cases where selection against hybridisation and divergent ecological selection are the driving forces of speciation.

Inferring the role of selection in shaping divergence and promoting isolation is not straightforward and I use the combination of phenotypic, genetic, and theoretical analyses to address this question. For example, I am developing comparative analyses in natural populations to test for the role of selection in generating divergence by comparing populations occurring in different selective environments. Another approach is to assess the genetic basis of divergence and the genetic architecture of diverging genome in order to test for signature of selection in genes involved in reproductive isolation. In this context, I am interested in population genomics approaches aiming at identifying "speciation genes" for example through candidate gene approach or analysing genome differentiation at larger scale.

Behavioural traits and speciation

I have been focusing on the evolution of behavioural traits responsible for the occurrence of premating isolation between populations. Among these behaviours I have been mainly working so far on the evolution of mate choice and habitat choice. I am using behavioural approaches to assess patterns of preference and assortative mating among populations and molecular approaches to address the genetic basis of such behavioural divergence. My interests are not taxon-specific, although I have particularly focused my attention on organisms using chemical cues to choose their mates and their breeding habitat, analysing how the evolution of chemically-based behaviours and chemical signals play a role in speciation (see a recent review paper I wrote on "chemosensory speciation").

My interest centres on the factors favouring the divergence of such behaviours, thus promoting speciation. Analysing variation of these behaviours in natural populations, the genetic architecture of behavioural divergence and the ecological factors associated with divergence helps me to gain insight into the mechanisms of behavioural divergence and the dynamics of such process. Selection often facilitates behavioural divergence, traits responsible for assortative mating evolving either under direct divergent selection or as a by product of selection acting on other traits (by linkage desequilibrium with traits involved for example in local adaptation). Through different biological cases and different approaches, my research aims at testing the role of selection in behavioural divergence, and at identifying the conditions favouring the rapid evolution of assortative mating (strength and modes of selection; modes of heritability: genetic, cultural etc.).