Abstract
Background and Aims The pseudometallophyte Noccaea caerulescens is an excellent model to study evolutionary processes, as it grows both on normal and on heavy-metal-rich, toxic soils. The evolution and demography of populations are critically impacted by mating system and, yet, information about the N. caerulescens mating system is limited.Methods Mean selfing rates were assessed using microsatellite loci and a robust estimation method (RMES) in five metallicolous and five non-metallicolous populations of N. caerulescens in Southern France, and this measure was replicated for two successive reproductive seasons. As a part of the study, the patterns of gene flow among populations were analysed. The mating system was then characterized at a fine spatial scale in three populations using the MLTR method on progeny arrays.Key Results The results confirm that N. caerulescens has a mixed mating system, with selfing rates ranging from 0·2 to 0·5. Selfing rates did not vary much among populations within ecotypes, but were lower in the metallicolous than in the non-metallicolous ecotype, in both seasons. Effective population size was also lower in non-metallicolous populations. Biparental inbreeding was null to moderate. Differentiation among populations was generally high, but neither ecotype nor isolation by distance explained it.Conclusions The consequences of higher selfing rates on adaptation are expected to be weak to moderate in non-metallicolous populations and they are expected to suffer less from inbreeding depression, compared to metallicolous populations.
Highlights
Organisms with the ability to grow on extremely toxic soils, such as mine wastes or mine smelters, have triggered a lot of interest recently (McNeilly and Antonovics, 1968; Antonovics et al, 1971; Bradshaw, 1984; Macnair, 1987; Pauwels et al, 2008)
The consequences of higher selfing rates on adaptation are expected to be weak to moderate in non-metallicolous populations and they are expected to suffer less from inbreeding depression, compared to metallicolous populations
Mean genetic diversity was higher in non-metallicolous populations than in metallicolous populations, the difference was not significant (MET 2012, 0Á54 6 0Á10 and MET 2013, 0Á55 6 0Á11; NONMET 2012, 0Á63 6 0Á04 and NONMET 2013, 0Á63 6 0Á04; permutation test, P2012 1⁄4 0Á13, P2013 1⁄4 0Á16; Table 2)
Summary
Organisms with the ability to grow on extremely toxic soils, such as mine wastes or mine smelters, have triggered a lot of interest recently (McNeilly and Antonovics, 1968; Antonovics et al, 1971; Bradshaw, 1984; Macnair, 1987; Pauwels et al, 2008). Noccaea caerulescens is one such organism, and is a model species for unravelling the genetic and physiological mechanisms of metal tolerance and hyperaccumulation (Assuncao et al, 2003b; Hanikenne and Nouet, 2011, and references therein), with potential applications in phytostabilization or phytoextraction (Chaney et al, 1997; but see Ernst, 2005). Noccaea caerulescens is a pseudometallophyte herb, as it can grow on both metal-rich soils and other types of soils. Noccaea caerulescens is an excellent model to investigate eco-evolutionary processes such as the adaptation to stressful environments or the evolution of local adaptation (Dubois et al, 2003; Dechamps et al, 2007; Jimenez-Ambriz et al, 2007; Noret et al, 2007; Besnard et al, 2009; Fones et al, 2013). Noccaea caerulescens is an excellent model to study evolutionary processes, as it grows both on normal and on heavy-metal-rich, toxic soils. The evolution and demography of populations are critically impacted by mating system and, yet, information about the N. caerulescens mating system is limited
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