Rapid Evolutionary Rates and Unique Genomic Signatures Discovered in the First Reference Genome for the Southern Ocean Salp, Salpa thompsoni (Urochordata, Thaliacea)

A preliminary genome sequence has been assembled for the Southern Ocean salp, Salpa thompsoni (Urochordata, Thaliacea). Despite the ecological importance of this species in Antarctic pelagic food webs and its potential role as an indicator of changing Southern Ocean ecosystems in response to climate change, no genomic resources are available for S. thompsoni or any closely related urochordate species. Using a multiple-platform, multiple-individual approach, we have produced a 318,767,936-bp genome sequence, covering \u3e50% of the estimated 602 Mb (±173 Mb) genome size for S. thompsoni. Using a nonredundant set of predicted proteins, \u3e50% (16,823) of sequences showed significant homology to known proteins and ∼38% (12,151) of the total protein predictions were associated with Gene Ontology functional information. We have generated 109,958 SNP variant and 9,782 indel predictions for this species, serving as a resource for future phylogenomic and population genetic studies. Comparing the salp genome to available assemblies for four other urochordates, Botryllus schlosseri, Ciona intestinalis, Ciona savignyi and Oikopleura dioica, we found that S. thompsoni shares the previously estimated rapid rates of evolution for these species. High mutation rates are thus independent of genome size, suggesting that rates of evolution \u3e1.5 times that observed for vertebrates are a broad taxonomic characteristic of urochordates. Tests for positive selection implemented in PAML revealed a small number of genes with sites undergoing rapid evolution, including genes involved in ribosome biogenesis and metabolic and immune process that may be reflective of both adaptation to polar, planktonic environments as well as the complex life history of the salps. Finally, we performed an initial survey of small RNAs, revealing the presence of known, conserved miRNAs, as well as novel miRNA genes; unique piRNAs; and mature miRNA signatures for varying developmental stages. Collectively, these resources provide a genomic foundation supporting S. thompsoni as a model species for further examination of the exceptional rates and patterns of genomic evolution shown by urochordates. Additionally, genomic data will allow for the development of molecular indicators of key life history events and processes and afford new understandings and predictions of impacts of climate change on this key species of Antarctic pelagic ecosystems

COI metabarcoding of zooplankton species diversity for time-series monitoring of the NW Atlantic continental shelf

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Bucklin, A., Batta-Lona, P., Questel, J., Wiebe, P., Richardson, D., Copley, N., & O’Brien, T. COI metabarcoding of zooplankton species diversity for time-series monitoring of the NW Atlantic continental shelf. Frontiers in Marine Science, 9, (2022): 867893, https://doi.org/10.3389/fmars.2022.867893.Marine zooplankton are rapid-responders and useful indicators of environmental variability and climate change impacts on pelagic ecosystems on time scales ranging from seasons to years to decades. The systematic complexity and taxonomic diversity of the zooplankton assemblage has presented significant challenges for routine morphological (microscopic) identification of species in samples collected during ecosystem monitoring and fisheries management surveys. Metabarcoding using the mitochondrial Cytochrome Oxidase I (COI) gene region has shown promise for detecting and identifying species of some – but not all – taxonomic groups in samples of marine zooplankton. This study examined species diversity of zooplankton on the Northwest Atlantic Continental Shelf using 27 samples collected in 2002-2012 from the Gulf of Maine, Georges Bank, and Mid-Atlantic Bight during Ecosystem Monitoring (EcoMon) Surveys by the NOAA NMFS Northeast Fisheries Science Center. COI metabarcodes were identified using the MetaZooGene Barcode Atlas and Database (https://metazoogene.org/MZGdb) specific to the North Atlantic Ocean. A total of 181 species across 23 taxonomic groups were detected, including a number of sibling and cryptic species that were not discriminated by morphological taxonomic analysis of EcoMon samples. In all, 67 species of 15 taxonomic groups had ≥ 50 COI sequences; 23 species had >1,000 COI sequences. Comparative analysis of molecular and morphological data showed significant correlations between COI sequence numbers and microscopic counts for 5 of 6 taxonomic groups and for 5 of 7 species with >1,000 COI sequences for which both types of data were available. Multivariate statistical analysis showed clustering of samples within each region based on both COI sequence numbers and EcoMon counts, although differences among the three regions were not statistically significant. The results demonstrate the power and potential of COI metabarcoding for identification of species of metazoan zooplankton in the context of ecosystem monitoring.This publication resulted in part from support provided by the Scientific Committee on Oceanic Research (SCOR). Funds were also contributed by the U.S. National Science Foundation (Grant OCE-1840868) and by national SCOR committees

Environmental Genomics and Transcriptomics of Salpa thompsoni and Population Genetic Variation of Euphausia superba in the Southern Ocean

The Western Antarctic Peninsula (WAP) region, which is experiencing increased sea surface temperatures, is a highly productive region of the Southern Ocean, supporting dense populations of the salp Salpa thompsoni and krill Euphuasia superba. Ecological data suggest that important species like salps and krill are being affected by climate change and that this effects on these planktonic species will have considerable consequences for the balance of the Southern Ocean ecosystem. The Antarctic krill E. superba is one of the best-studied marine zooplankton species in terms of population genetic diversity and structure. However few studies have discriminated life stages and examined sub-regional scale population genetic variation. Analysis of molecular variation revealed no significant differentiation between years, however larger levels of differentiation were observed among samples when furcilia larval stages were analyzed separately, and among life stages in the 2001 collection from Marguerite Bay. On the other hand the Southern Ocean S. thompsoni is subject to variable environmental and biological conditions, as well as the marked seasonal variability and long-term climate change. Knowledge of the physiology and molecular biology is imminent; one of the approaches that can be used is whole genome and transcriptome sequencing. The draft genome provided the first basis for the construction of an annotated gene catalog for S. thompsoni, a much-needed tool to understand the physiological response to environmental condition at a molecular level. Transcriptome analysis showed clear differentiation of gene expression patterns for a wide diversity of genes in salp samples from different regions, seasons, and samples