From Genomes to Populations: A Meta-analysis and Review of Fern Population Genetics

Abstract

Premise of research. Numbering around 10,000 species, ferns are the second-largest group of vascular plants. Relatively little work, however, has focused on the population genetic processes driving fern evolution. Early work by pteridologists suggested that ferns should be highly inbred (via gametophytic selfing) and therefore should have exceptionally low genetic diversity, with most genetic variation derived from polyploidy.Methodology. We conducted a meta-analysis, starting with literature searches using Google Scholar and Web of Science, to identify studies on fern population genetics. From these papers, we recorded population genetic metrics including expected heterozygosity under Hardy-Weinberg equilibrium (He), percent of polymorphic loci (%P), the inbreeding coefficient (F), Wright’s fixation index (FST), the molecular marker(s) used, and the geographic origin of the samples. We compared these metrics among ferns with various mating systems and growth habits.Pivotal results. We compiled a data set of 156 fern taxa from 87 publications. We found that both mating system and growth habit have a significant impact on the genetic diversity (%P) and population structuring of fern populations (F, FST). We found that temperate regions are the most thoroughly sampled and that most studies have used allozymes, with a shift in marker usage in the 2000s and 2010s.Conclusions. Contrary to early hypotheses, natural fern populations are not restricted to gametophytic selfing and instead regularly outcross. As we anticipate rapid growth in this field in the near future, we present a review of the major findings in fern population genetics to date. We also suggest possible future directions such as expanding geographic and taxonomic sampling and highlighting methods that will capitalize on the rapidly expanding genomic resources for ferns.