Genetic structure and mating systems of metallicolous and nonmetallicolous populations of Thlaspi caerulescens

Abstract

Summary• Genetic variation structure and breeding system were investigated in metallicolous (MET) and nonmetallicolous (NONMET) populations of the heavy-metal hyperaccumulator Thlaspi caerulescens from Belgium, Luxembourg and the French Mediterranean region.• Allozyme variation showed a clear differentiation between the two ecotypes in Belgium and Luxembourg but not in southern France, in line with the lower degree of geographical isolation between the two ecotypes in this region.• In both regions inbreeding coefficient ( F IS ) of NONMET populations was significantly higher compared to MET populations. Pollen/Ovule ratios were significantly higher in MET compared with NONMET populations.• These results suggest that NONMET populations of T. caerulescens are more selffertile than their MET counterparts. This contrasts with earlier studies on other metal-tolerant species in which selfing rates were higher in MET populations. This pattern may be explained by the fact that both ecotypes are not in sympatry in the populations studied, and therefore reproductive isolation has not been selected to maintain the adaptations to metal-contaminated soils. In addition, higher selfing rates in NONMET populations may have evolved as a mechanism of reproductive assurance, because these populations generally are at low densities.

Gene polymorphisms for elucidating the genetic structure of the heavy-metal hyperaccumulating trait in Thlaspi caerulescens and their cross-genera amplification in Brassicaceae

“…The F is values for the Swiss populations was comprised between 0.33 (A5, J12) and 0.44 (J8 ; Table 4). Interestingly, the fixation index of Prayon obtained with the variable loci of the present study (F is = 0.42) was close to the one reported with isozyme markers (F is = 0.51; Dubois et al 2003). In contrast, the lowest fixation index was found for Ganges (F is = 0.15).…”

“…When an excess of homozygotes was observed, a null allele estimator for nonequilibrium populations was used to estimate null allele frequencies (Van Oosterhout et al 2006). As the algorithm requires preliminary and independent estimate of fixation index (F is ), two F is were used, 0.36 and 0.64, corresponding respectively to fixation indices found on allozymes in metalliferous (from France and Belgium) and nonmetalliferous (from France and Luxembourg) T. caerulescens populations (Dubois et al 2003).…”

“…Compared with isozyme markers, which present a limited level of variation (maximum of four alleles; Dubois et al 2003), use of the present markers will be more suitable to study T. caerulescens natural populations. However, several additional remarks have to be considered for their application in population genetics.…”

“…Tolerance and hyperaccumulation for these metals was found to be highly variable between populations (Roosens et al 2003). Isozyme markers have been developed to analyse the systematic, the population genetic structure and the mating system of T. caerulescens (Koch et al 1998;Dubois et al 2003). These reports, as well as a phylogeographic reconstruction, may bring new insights into the understanding of the evolution of heavy-metal tolerance or hyperaccumulation in T. caerulescens.…”

“…Two fixation indices previously calculated for metallicolous (F is M = 0.36) and nonmetallicolous (F is NM = 0.64) Thlaspi caerulescens populations were used for simulations(Dubois et al 2003) …”