Assessing gene flow between Dicranum scoparium Hedw. and D. bonjeanii De Not. (Dicranaceae) using single nucleotide polymorphisms (SNPs)

While hybridization in vascular plants has received considerable attention, hybridization in bryophytes is still relatively understudied. Here we investigate hybridization between two species from the moss genus Dicranum. Hedw. Dicranum scoparium Hedw. and D. bonjeanii De Not. are two moss species of the D. scoparium species complex with partially overlapping morphology and habitat ranges. This study aimed to investigate a potential hybridization pathway between the two species by using single nucleotide polymorphisms (SNP), morphologically identifying the sex of the specimens and analyzing potential sex-specific SNP-markers, focusing on southern Sweden. The species differ by D. scoparium being polymorphic and D. bonjeanii monomorphic for the used SNP-markers. The SNP-markers genetically separate D. scoparium and D. bonjeanii specimens, though admixture between the species was observed on a limited scale. This admixture appears to originate from unidirectional fertilization of D. bonjeanii by D. scoparium (with a genome skewed towards D. scoparium as a result), possibly followed by back-crossing of first-generation hybrids with D. scoparium. Male expressing specimens were completely absent in the D. bonjeanii sample, making a fertilization of D. bonjeanii by males of D. scoparium more likely. No sex-specificity was observed in the used SNP-markers.

Methods
Moss samples of the species Dicranum scoparium Hedw. and Dicranum bonjeanii De Not. were collected in the most southern province of Sweden, Scania. DNA was extracted by using the Qiagen DNeasy Plant mini kit (www.qiagen.com) and an adapted version of the manifacturer's protocol. SNPs were selected from markers retrieved by Lang, Gehrmann and Cronberg (2021).

The samples included in the sequencing were those collected in Sweden as well as older extracts from Lang & Stech (2014) that were stored at Naturalis Biodiversity Center (NL). Sequencing was executed at the Mutation Analysis Facility (Karolinska University Hospital), with an Agena Massarray Analyzer.

References:

Lang AS, Stech M, What’s in a Name? Disentangling the Dicranum scoparium species complex (Dicranaceae, Bryophyta). Systematic Botany 2014; 39: 369-379
Lang AS, Gehrmann T, Cronberg N, Genetic Diversity and Population Structure in Bryophyte With Facultative Nannandry. Frontiers in Plant Science 2021; 12: 517547