A comparison of molecular markers and morphology for Neidium taxa (Bacillariophyta) from eastern North America

Abstract

Historically, a morphological species concept has applied shape subjectively in the delimitation of diatom species. This has led to confusion between taxa within the benthic diatom genus Neidium. Samples from Ontario, Quebec, Nova Scotia, Newfoundland (Canada) and New York (USA) were examined for Neidium taxa under LM and SEM. Fourier shape analysis showed that shape as a taxonomic character was not able to discern all species. Isolated individuals from the samples were amplified and sequenced for three chloroplast molecular markers (rbcL, psbC, and psbA) and one nuclear ribosomal molecular marker (18S). Phylogenetic reconstructions were completed with the concatenated chloroplast and 18S dataset using Maximum Likelihood and Bayesian analyses. The concatenated chloroplast dataset exhibited a species-level resolution phylogeny of Neidium taxa. The 18S dataset had a lower level of sequence divergence and was unable to differentiate between Neidium taxa. We present emended species descriptions and sequence data for four previously described species: Neidium sacoense, N. longiceps, N. fossum, and N. affine. We describe three novel species (Neidium lowei, N. promontorium, and N. potapovae) and identify two forms with unique molecular signatures. The distinguishing features of N. lowei are its size, valve shape, and longitudinal canal structure. Distinguishing features of N. promontorium are its valve shape, longitudinal canal and apex formation, and surface depression along the axial area. Neidium potapovae is distinguished by its size, formation of valve and apices and single longitudinal canal. This paper demonstrates how future phylogenetic treatments using single cell multigene sequencing can help resolve taxonomic confusion within diatoms.

<p><strong>Novel<em> Neidium </em>Pfitzer species from western Canada based upon morphology and plastid DNA sequences</strong></p>

“…It is evident that genetic and morphological metrics in combination will be required to identify species and ultimately the phylogeny of the genus Neidium. Neidium hitchcockii is presently the most distinct taxon based on morphology and nuclear and plastid DNA sequence data , Lefebvre et al 2017. We hypothesized that longitudinal canal formation (specifically number) would be integral in subgeneric evolutionary processes linked to the importance of locomotion in diatom evolution (Nakov et al 2018).…”

“…Phytotaxa 419 (1) © 2019 Magnolia Press • 57 1856: 8) R. Ross (1947: 210) from North America (Lefebvre et al 2017), but separated by larger size (N. longiceps 28-47 μm long, 8-12 μm wide), and lower stria count (N. longiceps 30-36 in 10 μm), and a distinct difference in the rbcL gene. All other morphological features are similar between the two taxa.…”

Paleolimnology and resurrection ecology: The future of reconstructing the past

“…The use of serial dilution enables greater ease of extracting and resuscitating dormant resting cells from lake sediments (Piredda et al., ). In addition to more efficient culturing of resting cells, single cell isolation and DNA extraction have proven successful for nuclear and chloroplast genomics (Lefebvre, Hamilton, & Pick, ; Pinseel et al., ). PCR amplification of DNA from single cells or dormant eggs could provide a suitable amount of genetic material from a small amount of source material for paleogenomic studies to forgo resurrection and culturing (Frisch et al., ; Hamilton, Lefebvre, & Bull, ).…”