ABSTRACT
The nivicolous species of the genus Diderma are challenging to identify, and there are several competing views on their delimitation. We analyzed 102 accessions of nivicolous Diderma spp. that were sequenced for two or three unlinked genes to determine which of the current taxonomic treatments is better supported by molecular species delimitation methods. The results of a haplotype web analysis, Bayesian species delimitation under a multispecies coalescent model, and phylogenetic analyses on concatenated alignments support a splitting approach that distinguishes six taxa: Diderma alpinum, D. europaeum, D. kamchaticum, D. meyerae, D. microcarpum and D. niveum. The first two approaches also support the separation of Diderma alpinum into two species with allopatric distribution. An extended dataset of 800 specimens (mainly from Europe) that were barcoded with 18S rDNA revealed only barcode variants similar to those in the species characterized by the first data set, and showed an uneven distribution of these species in the Northern Hemisphere: Diderma microcarpum and D. alpinum were the only species found in all seven intensively sampled mountain regions. Partial 18S rDNA sequences serving as DNA barcodes provided clear signatures that allowed for unambiguous identification of the nivicolous Diderma spp., including two putative species in D. alpinum.
Subject(s)
Myxomycetes , DNA Barcoding, Taxonomic/methods , Bayes Theorem , Phylogeny , DNA, Ribosomal/geneticsABSTRACT
A new species of Lamproderma (Myxomycetes), described herein as L. vietnamense, was recovered in the field on ground litter from mountain subtropical forests (Phia Oac - Phia Dén National Park) of northern Vietnam. Morphological details were examined by light and scanning electron microscopy. The species is characterized by a distinct and unique combination of morphological features, including a bright blue, shiny and very thin membranous peridium, a small dome-shaped columella, rigid, straight, branched, brown capillitial threads which gradually become pale at the periphery and finally colorless at the tips and small-meshed, banded-reticulate spores with 9-12 meshes across the spore diameter and solid walls without perforations 0.3-0.5 µm high. The stability of the taxonomic characters of L. vietnamense is supported by two well-developed collections found in 2018 and 2019. Partial sequences of three molecular markers (SSU, EF1α, COI) for both collections are identical. A two-gene phylogeny of the first two markers displays the two known accessions as a well-separated entity and indicates affinity of the new species with L. columbinum (the type taxon of the genus), L. violaceum, and several nivicolous Lamproderma species.
ABSTRACT
Myxomycetes are terrestrial protists with many presumably cosmopolitan species dispersing via airborne spores. A truly cosmopolitan species would suffer from outbreeding depression hampering local adaptation, while locally adapted species with limited distribution would be at a higher risk of extinction in changing environments. Here, we investigate intraspecific genetic diversity and phylogeography of Physarum albescens over the entire Northern Hemisphere. We sequenced 324 field collections of fruit bodies for 1-3 genetic markers (SSU, EF1A, COI) and analysed 98 specimens with genotyping by sequencing. The structure of the three-gene phylogeny, SNP-based phylogeny, phylogenetic networks, and the observed recombination pattern of three independently inherited gene markers can be best explained by the presence of at least 18 reproductively isolated groups, which can be seen as cryptic species. In all intensively sampled regions and in many localities, members of several phylogroups coexisted. Some phylogroups were found to be abundant in only one region and completely absent in other well-studied regions, and thus may represent regional endemics. Our results demonstrate that the widely distributed myxomycete species Ph. albescens represents a complex of at least 18 cryptic species, and some of these seem to have a limited geographical distribution. In addition, the presence of groups of presumably clonal specimens suggests that sexual and asexual reproduction coexist in natural populations of myxomycetes.
