Lower selfing rates in metallicolous populations than in non-metallicolous populations of the pseudometallophyteNoccaea caerulescens(Brassicaceae) in Southern France

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.

Evolutionary dynamics of quantitative variation in an adaptive trait at the regional scale: The case of zinc hyperaccumulation in Arabidopsis halleri

“…However, only few studies on pseudometallophytes have actually detected a reduced level of neutral genetic variation in M compared to NM populations (Babst‐Kostecka et al., ; Mengoni et al., ). Many studies found no difference (Baumbach & Hellwig, ; Bizoux et al., ; Pauwels et al., ), and the reverse situation (higher variation in M populations) has also been reported (Mousset et al., ; Słomka et al., ). In accordance with previous genetic investigations on A. halleri (Pauwels et al., ), we did not find any significant differences between the two edaphic groups for either expected heterozygosity or allelic richness.…”

“…However, only few studies on pseudometallophytes have actually detected a reduced level of neutral genetic variation in M compared to NM populations (Babst- Kostecka et al, 2014;Mengoni et al, 2001). Many studies found no difference (Baumbach & Hellwig, 2007;Bizoux et al, 2008;Pauwels et al, 2005), and the reverse situation (higher variation in M populations) has also been reported (Mousset et al, 2016;Słomka et al, 2011).…”

An evolutionary and functional genomics study of Noccaea caerulescens, a heavy metal hyperaccumulating plant species

“…One explanation for the observed phenotypic variation would be that outcrossing has occurred between the identified mutants and neighbouring plants. Although N. caerulescens is predominantly self-fertilizing with a cross-fertilization rate in the field ranging from 5-10% under normal growth conditions (Riley, 1956;Mousset et al, 2016), this could be higher if either the growth conditions or the mutagenesis process caused some (male) sterility, as was described for sorghum (Xin et al, 2008). Alternatively, the mutant itself could be partially selfsterile.…”

“…1).The flowering time differs among N. caerulescens accessions depending on the length of the vernalisation treatment. Both GA and SF are biennials from a relative dry region in the south of France with a short winter (Dubois, 2005) (Mousset et al, 2016). Consistent with this, a faster vernalisation response is predicted to confer a selective advantage to plants that flower earlier and thus avoid early summer droughts and high temperatures that result in poor seed set.…”

“…A. lyrata, as a self-incompatible, perennial species (Ross-Ibarra et al, 2008), is expected to have higher variability than the selfcompatible, usually self-pollinating, biennial/perennial species N. caerulescens (Riley, 1956;Koch et al, 1998;Dubois et al, 2003;Mousset et al, 2016). Furthermore, the outcrossing rate in N. caerulescens was found to be higher in metallicolous populations (Koch et al, 1998;Mousset et al, 2016), Given the shorter generation time and the higher selfing rate in N. caerulescens, it may be expected that local adaptation proceeds faster in this species in comparison with A. lyrata. The founder effects due to mine-to-mine seed transport by mine workers may also have promoted population differentiation, at least with regard to metal tolerance, between metallicolous and non-metallicolous of N. caerulescens, and decreased genetic variation in metallicolous populations.…”