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Phylogenetic diversity in freshwater-dwelling Isochrysidales haptophytes with implications for alkenone production.

ABSTRACT: Members of the order Isochrysidales are unique among haptophyte lineages in being the exclusive producers of alkenones, long-chain ketones that are commonly used for paleotemperature reconstructions. Alkenone-producing haptophytes are divided into three major groups based largely on molecular ecological data: Group I is found in freshwater lakes, Group II commonly occurs in brackish and coastal marine environments, and Group III consists of open ocean species. Each group has distinct alkenone distributions; however, only Groups II and III Isochrysidales currently have cultured representatives. The uncultured Group I Isochrysidales are distinguished geochemically by the presence of tri-unsaturated alkenone isomers (C_37:3b Me, C_38:3b Et, C_38:3b Me, C_39:3b Et) present in water column and sediment samples, yet their genetic diversity, morphology, and environmental controls are largely unknown. Using small-subunit (SSU) ribosomal RNA (rRNA) marker gene amplicon high-throughput sequencing of environmental water column and sediment samples, we show that Group I is monophyletic with high phylogenetic diversity and contains a well-supported clade separating the previously described "EV" clade from the "Greenland" clade. We infer the first partial large-subunit (LSU) rRNA gene Group I sequence phylogeny, which uncovered additional well-supported clades embedded within Group I. Relative to Group II, Group I revealed higher levels of genetic diversity despite conservation of alkenone signatures and a closer evolutionary relationship with Group III. In Group I, the presence of the tri-unsaturated alkenone isomers appears to be conserved, which is not the case for Group II. This suggests differing environmental influences on Group I and II and perhaps uncovers evolutionary constraints on alkenone biosynthesis.

SUBMITTER: Richter N

PROVIDER: S-EPMC6590312 | biostudies-literature | 2019 May

REPOSITORIES: biostudies-literature

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Phylogenetic diversity in freshwater-dwelling Isochrysidales haptophytes with implications for alkenone production.

Richter Nora N Longo William M WM George Sarabeth S Shipunova Anna A Huang Yongsong Y Amaral-Zettler Linda L

Geobiology 20190205 3

Members of the order Isochrysidales are unique among haptophyte lineages in being the exclusive producers of alkenones, long-chain ketones that are commonly used for paleotemperature reconstructions. Alkenone-producing haptophytes are divided into three major groups based largely on molecular ecological data: Group I is found in freshwater lakes, Group II commonly occurs in brackish and coastal marine environments, and Group III consists of open ocean species. Each group has distinct alkenone di ...[more]

PMID: 30720914

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Project description:The Green River in Kentucky in the eastern United States is a freshwater mussel biodiversity hotspot, with 71 known species. Among them, the endangered Pleurobema plenum coexists with other morphologically similar species in the genera Fusconaia and Pleurobema, known colloquially as "pigtoes." Identification of species in these genera is challenging even for mussel experts familiar with them. In our study, the correct identification of these species by experts ranged from 57% to 83%. We delineated taxonomic boundaries among seven species and tested for cryptic biodiversity among these look-alike mussels utilizing mitochondrial and nuclear DNA sequence variation. Phylogenetic analysis of combined (1215 bp) mitochondrial DNA cytochrome oxidase I (COI) and NADH dehydrogenase 1 (ND1) genes showed five well-diverged groups that included F. flava, F. subrotunda, P. cordatum, and P. plenum as distinct clades, with P. sintoxia and P. rubrum grouped into a single clade. While our mitochondrial DNA analyses did not distinguish P. sintoxia and P. rubrum as phylogenetically distinct species, the typical shell forms of these two nominal taxa are very distinct. Further phylogenetic analysis using nuclear ribosomal transcribed spacer region subunit I (ITS1) DNA sequences also showed that P. sintoxia and P. rubrum were not distinct lineages. No cryptic species were detected in the Fusconaia and Pleurobema samples analyzed from the Green River. The highest haplotype diversity (h), average number of nucleotide differences (k), and nucleotide diversity (π) were observed for F. subrotunda at both the COI (h = 0.896, k = 3.805, π = 0.00808) and ND1 (h = 0.984, k = 6.595, π = 0.00886) markers, with similarly high genetic diversity in the other taxa. Our results give managers confidence that cryptic taxa do not occur within or among these morphologically similar species in the Green River, and populations appear genetically diverse, indicative of large and healthy populations.

Dataset Information

Phylogenetic diversity in freshwater-dwelling Isochrysidales haptophytes with implications for alkenone production.

Publications

Phylogenetic diversity in freshwater-dwelling Isochrysidales haptophytes with implications for alkenone production.

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