UNIVERSITE DE BOURGOGNE THÈSE Yongbo LIU - Université de ...

Introduction
Spontaneous introgression from crops to their relatives should be evaluated as a component of
the r isk a ssessment for t he release of g enetically m odified ( GM) c rops (Darmency 1994;
Ellstrand e t a l. 1999) . S everal s tudies on a dvanced-generation h ybrids f ind t hat s ome
interspecific hybrid genotypes persist for several generations under certain conditions, which
suggests th at long-term introgression could o ccur under natural environments ( Linder et al.
1998; Lexer et al. 2003; Al Mouemar and Darmency 2004; Warwick et al. 2008).
Studies on t he di rect fitness e ffects of t ransgenes on i ntrogressed pr ogeny aid i n
assessing their ph enotype a nd t heir effect on t he d ynamics a nd de mography of t he
introgressed populations. The rate of transgene spread is mainly governed by fitness effects
(Rieseberg and Burke 2001). However, most experimental studies only involved F 1 hybrids
that may display either heterosis, a transient condition that may overestimate the probability
of persistence of crop genes within wild populations (Arnold and Hodges 1995; Lexer et al.
2003), or out breeding de pression a nd ne ar s terility, a t ransient c ondition th at ma y
underestimate the probability of persistence of crop genes within wild populations (Burke and
Arnold 2001) . S uch i nteracting e ffects a re r educed i n a dvanced generations of ba ckcrossed
progeny t hat ar e b etter s uited m aterial t o es timate t he b enefice a nd c ost of a n i ntrogressed
transgene in a wild population.
As t ransgene i ntrogression w ill i nevitably l ead t o popul ations c omposed of bot h
transgenic a nd non -transgenic p rogeny ( Vacher et al . 2 004), t he f ecundity and r esulting
evolutionary impact o f crop-wild in trogressed o ffspring ma y d epend o n th eir c ompetition
ability (Campbell a nd Snow 2007) . T ransgenic pl ants ge nerally a re expected t o be a t
competitive a dvantage when t ransgenes i nvolve f itness-related tr aits, lik e th e Bacillus
thuringiensis (Bt), insect-resistance transgene. Wild plants receiving the Bt gene are likely to
display i nsect-resistance a nd l ess he rbivore d amage a s Bt c rops do, w hich i n t urn c onfers
greater pl ant f itness ( survival, g rowth a nd f ecundity pot entiality) c ompared w ith i nsectsusceptible
plants (Stewart et al. 1996; Ramachandran et al. 2000; Snow et al. 2003; Vacher et
al. 2004; M oon e t al. 2007). A s t he f itness a dvantage o f i nsect-resistance allows h igher
competition, the resistant plants are expected to suppress the growth of susceptible ones in the
populations i n w hich t he t rangene m ove i n. H owever, t he d ynamics of m ixed popul ations
including r esistant a nd s usceptible pl ants m ight be a c omplex pr ocess, de pending on
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