Assessing Global DNA Methylation Changes Associated with Plasticity in Seven Highly Inbred Lines of Snapdragon Plants (Antirrhinum majus).

Genetic and epigenetic variations are commonly known to underlie phenotypic plastic responses to environmental cues. However, the role of epigenetic variation in plastic responses harboring ecological significance in nature remains to be assessed. The shade avoidance response (SAR) of plants is one of the most prevalent examples of phenotypic plasticity. It is a phenotypic syndrome including stem elongation and multiple other traits. Its ecological significance is widely acknowledged, and it can be adaptive in the presence of competition for light. Underlying genes and pathways were identified, but evidence for its epigenetic basis remains scarce. We used a proven and accessible approach at the population level and compared global DNA methylation between plants exposed to regular light and three different magnitudes of shade in seven highly inbred lines of snapdragon plants (Antirrhinum majus) grown in a greenhouse. Our results brought evidence of a strong SAR syndrome for which magnitude did not vary between lines. They also brought evidence that its magnitude was not associated with the global DNA methylation percentage for five of the six traits under study. The magnitude of stem elongation was significantly associated with global DNA demethylation. We discuss the limits of this approach and why caution must be taken with such results. In-depth approaches at the DNA sequence level will be necessary to better understand the molecular basis of the SAR syndrome.

Quantitative Trait Locus Analysis of Mating Behavior and Male Sex Pheromones in Nasonia Wasps.

A major focus in speciation genetics is to identify the chromosomal regions and genes that reduce hybridization and gene flow. We investigated the genetic architecture of mating behavior in the parasitoid wasp species pair Nasonia giraulti and Nasonia oneida that exhibit strong prezygotic isolation. Behavioral analysis showed that N. oneida females had consistently higher latency times, and broke off the mating sequence more often in the mounting stage when confronted with N. giraulti males compared with males of their own species. N. oneida males produce a lower quantity of the long-range male sex pheromone (4R,5S)-5-hydroxy-4-decanolide (RS-HDL). Crosses between the two species yielded hybrid males with various pheromone quantities, and these males were used in mating trials with females of either species to measure female mate discrimination rates. A quantitative trait locus (QTL) analysis involving 475 recombinant hybrid males (F2), 2148 reciprocally backcrossed females (F3), and a linkage map of 52 equally spaced neutral single nucleotide polymorphism (SNP) markers plus SNPs in 40 candidate mating behavior genes revealed four QTL for male pheromone amount, depending on partner species. Our results demonstrate that the RS-HDL pheromone plays a role in the mating system of N. giraulti and N. oneida, but also that additional communication cues are involved in mate choice. No QTL were found for female mate discrimination, which points at a polygenic architecture of female choice with strong environmental influences.

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

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.

Characterization and multiplexing of 21 microsatellite markers for the herb Noccaea caerulescens (Brassicaceae).

PREMISE OF THE STUDY: Multiplexed microsatellite markers were developed for population genetic studies in the pseudometallophyte Noccaea caerulescens (Brassicaceae), a model species to investigate metal tolerance and hyperaccumulation in higher plants. METHODS AND RESULTS: Microsatellite loci were isolated through pyrosequencing of an enriched DNA library. Three multiplexes combining four previously published and 17 newly designed markers were developed. The new markers were screened in metallicolous and nonmetallicolous populations from southern France. The total number of alleles per locus ranged from five to 18. The observed heterozygosity per locus and per population ranged from 0 to 0.83, and expected heterozygosity ranged from 0 to 0.89. CONCLUSIONS: The investigated loci showed reasonable to high levels of polymorphism at the regional scale. The multiplex set should be helpful in investigating genetic diversity, population structure, and demographic history in N. caerulescens at various spatial scales.

Strong inbreeding depression in two Scandinavian populations of the self-incompatible perennial herb Arabidopsis lyrata.

Inbreeding depression is a key factor influencing mating system evolution in plants, but current understanding of its relationship with selfing rate is limited by a sampling bias with few estimates for self-incompatible species. We quantified inbreeding depression (δ) over two growing seasons in two populations of the self-incompatible perennial herb Arabidopsis lyrata ssp. petraea in Scandinavia. Inbreeding depression was strong and of similar magnitude in both populations. Inbreeding depression for overall fitness across two seasons (the product of number of seeds, offspring viability, and offspring biomass) was 81% and 78% in the two populations. Chlorophyll deficiency accounted for 81% of seedling mortality in the selfing treatment, and was not observed among offspring resulting from outcrossing. The strong reduction in both early viability and late quantitative traits suggests that inbreeding depression is due to deleterious alleles of both large and small effect, and that both populations experience strong selection against the loss of self-incompatibility. A review of available estimates suggested that inbreeding depression tends to be stronger in self-incompatible than in self-compatible highly outcrossing species, implying that undersampling of self-incompatible taxa may bias estimates of the relationship between mating system and inbreeding depression.