Journal of Phycology最新文献

This study examines how hyposaline stress impacts the early life-stages of commercial kelp species from Alaska. Kelp are important species both ecologically and commercially and are likely to experience significant impacts due to ongoing climate change. Climate-driven glacial melt and changing rainfall patterns globally will release large amounts of freshwater into coastal systems in the coming decades. Both bull kelp (Nereocystis luetkeana) and ribbon kelp (Alaria marginata) are high-latitude species of commercial and ecological importance. These species inhabit very different environments: While bull kelp is a subtidal, canopy-forming species, ribbon kelp is an intertidal subcanopy species. In this study, fertile specimens of both were collected from various locations in Alaska and induced to release spores. These were cultivated for 30 days in four salinity treatments: 32, 25, 20, and 13. Both species grew and produced gametophytes in salinities down to a salinity of 20, although A. marginata seems to be better adapted to hyposaline conditions. Below a salinity of 20, we observed several impacts on progression between life stages. The response of gametophyte growth and the production of eggs and sporophytes to different salinities varied both by species and by population. Gametophytes of N. luetkeana grew fastest at a salinity of 32, while those of A. marginata grew fastest between 20 and 25 (Juneau) or 25 and 32 (Kodiak). In terms of egg production, A. marginata displayed significant population-level variation. Juneau individuals produced the same number of eggs regardless of salinity. Kodiak individuals produced fewer eggs in hyposaline conditions. The production of sporophytes from eggs for both species from all locations was unaffected by salinities above 20; however, no sporophytes at all were produced at 13. All of this has implications for commercial production in the hatchery phase, as hyposaline stress may induce N. luetkeana to produce sporophytes faster than in full oceanic salinity. In terms of wild populations, the observed population-level and species-level differences in adaptation to hyposaline conditions suggest that decreased salinities in coastal areas are likely to impact the distribution of these two species over the coming decades.

Temporal population genetic studies have investigated evolutionary processes, but few have characterized reproductive system variation. Yet, temporal sampling may improve our understanding of reproductive system evolution through the assessment of the relative rates of selfing, outcrossing, and clonality. In this study, we focused on the monoicous, haploid-diploid freshwater red alga Batrachospermum gelatinosum. This species has a perennial, microscopic diploid phase (chantransia) that produces an ephemeral, macroscopic haploid phase (gametophyte). Recent work focusing on single-time point genotyping suggested high rates of intragametophytic selfing, although there was variation among sites. We expand on this work by genotyping 191 gametophytes sampled from four sites that had reproductive system variation based on single-snapshot genotyping. For this study, we sampled at multiple time points within and among years. Results from intra-annual data suggested shifts in gametophytic genotypes throughout the season. We hypothesize that this pattern is likely due to the seasonality of the life cycle and the timing of meiosis among the chantransia. Interannual patterns were characterized by consistent genotypic and genetic composition, indicating stability in the prevailing reproductive system through time. Yet, our study identified limits by which available theoretical predictions and analytical tools can resolve reproductive system variation using haploid data. There is a need to develop new analytical tools to understand the evolution of sex by expanding our ability to characterize the spatiotemporal variation in reproductive systems across diverse life cycles.

Diatoms are an important component of marine and freshwater ecosystems. Although the majority of described diatom species live in freshwater systems, genome sequencing efforts have focused primarily on marine species. Genomic resources for freshwater species have the potential to improve our understanding of diatom ecology and evolution, particularly in the context of major environmental shifts. We used long- and short-read sequencing platforms to assemble reference genomes for three freshwater diatom species, all in the order Thalalassiosirales, which are abundant in the plankton of oceans, lakes, reservoirs, and rivers worldwide. We targeted three species that cover the breadth of phylogenetic diversity in the cyclostephanoid clade of Thalassiosirales: Cyclostephanos tholiformis (JALLPB020000000), Discostella pseudostelligera (JALLBG020000000), and Praestephanos triporus (JALLAZ020000000). The reference genome for D. pseudostelligera was considerably smaller (39 Mb) than those of both P. triporus (73 Mb) and C. tholiformis (177 Mb). Long-read sequencing allowed for the assembly of scaffold-level genomes, including regions rich in repetitive DNA. Compared to short-read assemblies, long-read assemblies increased the contig N50 length as much as 37-fold and reduced the number of contigs by more than 88%. Transcriptome-guided annotation of the protein-coding genes identified between 10,000 and 12,000 genes. This work provides further demonstration of the value of long-read sequencing and provides novel genomic resources for understanding the ecology and evolution of freshwater diatoms.

Investigating taxa at varying stages of divergence can shed light on the evolutionary forces that lead to reproductive isolation and eventual speciation. The forces promoting isolation vary in space and time, which makes it difficult to reconstruct the trajectory that resulted in the divergence observed among species today. The red macroalgal genus Plocamium is known worldwide for its cryptic genetic and chemical diversity. Previous work on the genus Plocamium in Antarctica observed two haplotypes along the western Antarctic Peninsula that have been treated as the same species. Using 10 microsatellite loci, we observed that these two haplotypes correspond to two highly divergent, co-occurring genetic entities in Antarctic Plocamium, which are located within close vicinity of each other at the same sites. The morphology of the reproductive structures, a feature commonly used to identify cryptic species in Plocamium, as well as the timing of reproduction, differed significantly between the two genetic entities. Altogether, this suggests that two Antarctic Plocamium species exist on the western Antarctic Peninsula. We observed evidence for high levels of selfing in both genetic entities, which likely exacerbated the lack of gene flow between them. In addition, we identified concomitant chemodiversity that generates compelling evidence of early evolutionary divergence within one of these entities. This chemodiversity has ecological consequences for its main grazer, which alludes to one putative evolutionary driver of divergence. Antarctic Plocamium spp. provide a promising model system for investigating the eco-evolutionary forces that initiate and maintain species boundaries.

The Indian subcontinent has emerged as a natural habitat to several cyanobacterial taxa which have been explored and described in the past few years using a polyphasic approach. Various new genera and species of Nostoc morphotypes, heteropolar unbranched as well as branched heterocytous cyanobacteria, have been described from various parts of India such as the central mainland, temperate hill stations of extreme northern India, and the biodiversity hotspots of northeast India. Konkan, a small strip of land bounded by Arabian sea on the west and Sahyadri mountains on the east, has various habitats such as coastal beds, old monuments, freshwater lakes, and rivers; however, this region has been less charted in modern cyanobacterial systematics, relative to others. The region has a tropical climate with heavy monsoon showers owing to its location on the windward side of the northern Western Ghats, a global biodiversity hotspot. Through this study, several districts of the Konkan region of Maharashtra and Goa were explored for cyanobacterial diversity and evaluated through a polyphasic approach with three novel species of the genus Desikacharya, two novel species of the genus Pseudoaliinostoc and one new species of the monotypic genus Chlorogloeopsis being described in accordance with the International Code of Nomenclature for algae, fungi and plants (ICN).

Phytoplankton plays a crucial role in the fate of pollutants in aquatic ecosystems by biotransformation and bioaccumulation. Aniline was listed in priority pollutants due to its toxicity and widespread distribution in the aquatic environment. This study focused on investigating the capacity and mechanism of eukaryotic alga Chlamydomonas reinhardtii in transforming aniline. Results showed that the total removal percentage of aniline was 56% within 8 days at an initial concentration of 10 mg · L^-1. The percentage of the biotransformation by C. reinhardtii was 23.4%. The biotransformation product was identified as acetanilide, indicating that acetylation was the primary biotransformation pathway. To reveal the key enzyme of the biotransformation process, the N-acetyltransferase (NAT) gene was cloned from the C. reinhardtii genome, and the NAT protein was obtained through heterologous expression. Aniline was significantly transformed by the purified NAT protein in vitro, and the product was also acetanilide. The characteristics of C. reinhardtii NAT in biotransformation of aniline was analyzed by bioinformatics methods. The binding sites in C. reinhardtii NAT for ligands (aniline and acetyl-CoA) were identified. Three highly reserved valine residues (Glu⁸⁵-Asp⁸⁶-Val⁸⁷-Val⁸⁸-Val⁸⁹) as well as GLU¹³¹ and Cys¹²² were the indispensable amino acid residues for the catalysis from aniline to acetanilide. These results demonstrated the capacity of C. reinhardtii in the biotransformation of aniline, and the transformation process was primarily through N-acetylation of aniline to acetanilide catalyzed by NAT enzyme. This study provides novel insights into the biotransformation mechanism of aniline in eukaryotic green alga C. reinhardtii, facilitating the evaluation of the fate of aniline within aquatic ecosystems.

Kelp forests are among the most abundant and productive marine ecosystems but are under threat from climate change and other anthropogenic stressors. Although knowledge is growing about how the abundance and distribution of kelp forests are changing, much less is known about the "non-lethal" effects that global change is having on the performance and health of kelp populations in areas where they persist. Here we assessed the age distribution of two common stipitate kelp species, Laminaria setchelli and Pterygophora californica, at Wizard Islet in Barkley Sound, British Columbia, Canada, and compared these data to historical demographic data collected by De Wreede (1984) and Klinger and DeWreede (1988) from the same site between 1981 and 1983. We observed that L. setchelli populations in 2020 were younger and less evenly aged than the same populations sampled nearly four decades prior, while the P. californica population was composed of older individuals on average than at the historical time point. Although the drivers of these demographic changes remain unclear, Barkley Sound has experienced substantial changes in the physical and biological environment over the past decade that could be responsible for these patterns. Given that the size of an individual and its probability of reproduction increases with age, shifting demographics may impact the reproductive output of each population, potentially altering the competitive relationships between co-occurring species. Changes in size distribution may also influence ecosystem-level processes such as habitat complexity or productivity.

The filamentous red algal genus Bryocladia was recently deeply revised based on molecular and morphological data. However, data from the Southwestern Atlantic Ocean are scarce. Here, we provide a phylogenetic study of Bryocladia representatives from the Brazilian coast with new additions to the genus. Our samples were collected from the north to southeastern Brazilian coast in marine and estuarine areas. We carried out a morphological and molecular study based on COI-5P and rbcL gene sequences. Our phylogenetic analyses confirmed the presence of seven species on the Brazilian coast, four of which were previously known: B. cuspidata, B. subtilissima, B. thyrsigera, and B. villum. Three new species are described here, B. itaipensis sp. nov., B. oceanica sp. nov., and B. mucuripensis sp. nov., all morphologically included in the B. scopulorum complex. Bryocladia subtilissima was observed only in Brazilian estuarine areas. However, it was split into two subclades, which require further investigation. The three new species expand the known diversity of the B. scopulorum complex from 12 to 15 species. Bryocladia itaipensis is closely related to B. canariensis and B. caespitosa, whereas B. oceanica and B. mucuripensis formed distinct lineages with unsolved relationships. All new species are restricted to their type localities in Brazilian waters, reinforcing the need for further study of tiny species, especially from the tribes Polysiphonieae and Streblocladieae.

Sea ice can profoundly influence photosynthetic organisms by altering subsurface irradiance, but it is susceptible to changes in the climate. The patterns and timing of sea ice cover can vary on a monthly to annual timescale in small sub-regions of the Western Antarctic Peninsula (WAP). During the latter part of the 20th century, sea ice coverage significantly decreased in the WAP, a trend that aligns with warming in this area. Macroalgal biochemical components are impacted by light availability, often showing a close relationship between photosynthesis and biochemical compositions. We used satellite imagery of annual sea ice duration and extent as well as water turbidity during ice-free periods to identify 14 study sites that differed dramatically in sea ice coverage but were similar in terms of turbidity along the central WAP between 68° S and 64° S. The common macroalgal species Desmarestia menziesii, Himantothallus grandifolius, Sarcopeltis antarctica, and Iridaea sp. were collected by scuba divers between 5 m and 35 m depth at each site where they occurred, for later biochemical analyses. Overall percentages of major biochemical components as well as carbon and nitrogen percentages and C:N were determined and correlated with four different sea ice indices. Surprisingly, most of the chemical components were not significantly correlated with sea ice cover. The few significant correlations varied between species and chemical components. This indicates that although patterns of sea ice coverage have major implications for macroalgal abundance, on a per-biomass basis, sea ice coverage does not impact the nutritional contributions of macroalgae to food webs.