Molecular evidence for convergent evolution and allopolyploid speciation within the Physcomitrium-Physcomitrellaspecies complex

Abstract

BackgroundThe moss Physcomitrella patens (Hedw.) Bruch & Schimp. is an important experimental model system for evolutionary-developmental studies. In order to shed light on the evolutionary history of Physcomitrella and related species within the Funariaceae, we analyzed the natural genetic diversity of the Physcomitrium-Physcomitrella species complex.ResultsMolecular analysis of the nuclear single copy gene BRK1 reveals that three Physcomitrium species feature larger genome sizes than Physcomitrella patens and encode two expressed BRK1 homeologs (polyploidization-derived paralogs), indicating that they may be allopolyploid hybrids. Phylogenetic analyses of BRK1 as well as microsatellite simple sequence repeat (SSR) data confirm a polyphyletic origin for three Physcomitrella lineages. Differences in the conservation of mitochondrial editing sites further support hybridization and cryptic speciation within the Physcomitrium-Physcomitrella species complex.ConclusionsWe propose a revised classification of the previously described four subspecies of Physcomitrella patens into three distinct species, namely Physcomitrella patens, Physcomitrella readeri and Physcomitrella magdalenae. We argue that secondary reduction of sporophyte complexity in these species is due to the establishment of an ecological niche, namely spores resting in mud and possible spore dispersal by migratory birds. Besides the Physcomitrium-Physcomitrella species complex, the Funariaceae are host to their type species, Funaria hygrometrica, featuring a sporophyte morphology which is more complex. Their considerable developmental variation among closely related lineages and remarkable trait evolution render the Funariaceae an interesting group for evolutionary and genetic research.

DNA based revised geographic circumscription of species of Physcomitrella s.l. (Funariaceae): P. patens new to East Asia and P. magdalenae new to East Africa

“…1), that are each maximally supported within the ITS dataset (PP51 and BS5100) and moderately to highly supported within the plastid dataset (PP $ 0.96 and BS $74). Such distribution into 3 lineages is further confirmed by inferences from variation in the four plastid loci sampled for 200 Funariaceae (results not shown), and is consistent with topologies presented by McDaniel et al (2010), Liu et al (2012) and Beike et al (2014). Inferences from variation in DNA sequences already prompted accommodating subsp.…”

“…We were unable to obtain the original voucher for the population of P. readeri from Del Valle Lake, California (listed as P. patens subsp. californica at the IMSC) resolved here and by McDaniel et al (2010) and Beike et al (2014) within P. patens. This phylogenetic placement led Beike et al (2014) to consider P. patens subsp.…”

“…californica at the IMSC) resolved here and by McDaniel et al (2010) and Beike et al (2014) within P. patens. This phylogenetic placement led Beike et al (2014) to consider P. patens subsp. californica (i.e., Physcomitridium readeri), and by extension, Physcomitridium to be polyphyletic.…”

“…Finally Liu et al (2012) confirmed, based on inferences from ten loci sampled for a broad set of Funariaceae exemplars, that the concept of a monophyletic Physcomitrella sensu Fife (1985) should be abandoned, but considering that exact affinities of each of the three taxa within the crown group of Funariaceae remained ambiguous, refrained from revising generic concepts. Most recently, Beike et al (2014) confirmed the phylogenetic structure within Physcomitrella based on a broader geographic sample of populations, but also suggested that P. readeri is polyphyletic based on a population from California (identified as Physcomitrella patens subsp. californica in the article) nested within P. patens s.str.…”

A taxonomic revision of cleistocarpous species of Weissia (Pottiaceae, Bryophyta) in Japan

“…It appears as if selective pressures or relaxation in highly seasonal habitats are driving the diversification rather than the conservation of sporophytic architecture . The relatively short branch length in the Japanese Weissia clade also suggests reticulate evolution within the genus, as recently shown in the Physcomitrium-Physcomitrella species complex (McDaniel et al 2010, Bike et al 2014. The hybrids are usually found among weedy and semi-weedy species, that is species with potential life spans of a few years, and their highly seasonal habitats promote the growth of colonies of different species in close proximity, increasing the chance of intermixing and cross fertilization (Anderson 1980, Natcheva & Cronberg 2004.…”