Outcrossing Mating System of the Early-Divergent Moonwort Fern (Botrychium lunaria, Ophioglossaceae) Revealed in the European Alps

Abstract

Premise of the Research. Vascular plants depend on sexual recombination for generating new genetic variability to meet environmental needs. Nevertheless, members of the earlydivergent fern genus Botrychium (Ophioglossaceae) typically maintain gametophytic selfing and show strong inbreeding within populations. To explain this evolutionary anomaly, the existence of previous or current but undiscovered outcrossing, genetically rich, precursors of the existing genetically depauperate taxa has been hypothesized. Methodology.Using allele expression at thirteen independently assorting enzyme loci, we compared allelic diversity and levels of heterozygosity in 471 Botrychium lunaria individuals across sixteen populations in the Alps and Jura Mountains of Switzerland. We examined habitat characteristics influencing mating systems and investigated population genetic structure based on a discriminant analysis of principal components and a graph-theoretic framework. We tested the pattern of isolation by distance and explored the biological processes favoring or limiting spore dispersal at a regional scale.Pivotal Results. We found high genetic diversity within and among populations, and similar observed (HO) and expected heterozygosity (HS) across loci (HO = 0.020-0.450 and HS = 0.040-0.590, respectively). Estimates of HO (0.050-0.272) were lower than HS (0.144-0.305) across individuals, indicating a weak deficit in heterozygotes. Mean values of departure (D) from expected heterozygosity were close to what would be expected with random mating (DL = 0.061 and DP = 0.059 across loci and populations, respectively). The mean inbreeding coefficient was low (FIS = 0.247) and the overall genetic differentiation was moderate (global FST = 0.083).Conclusions. Together, the discriminant analysis of principal components and the Population Graph revealed a complex population genetic structure and a weak genetic differentiation with substantial gene flow among most populations. One population (Arosa), sampled from a 3 site recently released from permafrost, demonstrated probable founder effect not correlated with geographical isolation. The topology of the Population Graph identified three subgroups with several key populations (BGU, CHL, GSB, SBE, and VRO) that maintained genetic connectivity of populations from distant locations.

Transcriptome‐wide SNPs for Botrychium lunaria ferns enable fine‐grained analysis of ploidy and population structure

“…Only one individual in the Chasseral population showed signature of a recent gametophytic selfing event (Figure4e). These findings contrast with the general assumption that gametophytic selfing is the dominant reproductive mode in the genus but corroborate evidence of outcrossing in Swiss populations(Dauphin et al, 2020).Our study establishes a high-quality set of transcriptome-wide SNPs in a species of the early diverging fern genus Botrychium. With an estimated genome size of 19.4-24.6 (2C; ~19.0-23.7 Gb) for B. lunaria, the assembly of transcriptomes provides the only currently feasible approach to generate extensive genome-wide markers information.…”

“…Phylogenies based only on few barcoding loci, but with a more representative sampling, identified Gleicheniales as being a monophyletic clade (Pryer et al, 2004;Schuettpelz et al, 2006;Schuettpelz & Pryer, 2007). Phylogenomic studies including the Matoniaceae will be needed to ascertain the 1 -5 0 0 5 0 0 -1 , 0 0 0 1 , 0 0 0 -1 , 5 0 0 1 , 5 0 0 -2 , 0 0 0 2 , 0 0 0 -4 , 0 0 0 4 , 0 0 0 -8 , 0 0 0 8 , 0 0 0 -1 0 , 0 0 0 1 0 , 0 0 0 -1 6 , 3 0 0 no meaningful genetic differentiation within populations (Farrar, 1998;Hauk & Haufler, 1999;Williams, 2021) or low genetic differentiation among populations (Birkeland et al, 2017;Camacho & Liston, 2001;Dauphin et al, 2020;Swartz & Brunsfeld, 2002).…”

Methodologies for soil extraction and conservation analysis of ferns and lycophytes with belowground gametophytes

“…Gametophyte diameters range from 1 to 2 mm. Photos reproduced with permission from Dauphin et al ( 2020 ).…”

A dormant resource for genome size estimation in ferns: C‐value inference of the Ophioglossaceae using herbarium specimen spores

“…Given the small size of our sample with both sporophytic and gametophytic data from the same individuals, further FCM work is needed for a conclusive determination of the reproductive modes of these fern species. Previous population genetic studies have shown that Ophioglossaceae species are primarily sexually reproducing (Watano and Sahashi, 1992 ; Chung et al, 2013 ; Dauphin et al, 2020 ; Williams, 2021 ; and references therein). One cytological report implies apomictic reproduction in an Ophioglossum species (Tindale and Roy, 2002 ; Brownsey and Perrie, 2015 ), but this requires further confirmation by comparing its spore and leaf genome sizes.…”