The chloroplast haplotypes, ecology, growth, and reproduction of the introduced Japanese green alga Codium fragile were evaluated in four salt marsh pannes from Brave Boat Harbor, Kittery, Maine. All chloroplast haplotypes were identical and they matched the subsp. fragile delineated by Provan et al. Frond stature was seasonally variable and showed a pronounced increase in length from summer to early fall. Residual (i.e., overwintering) spring fronds were highly variable in stature compared to previous fall values, with some fronds only being ~ 0.5–1.0 cm. Frond stature and frequency patterns in the different pannes were related to their proximity to tidal channels, plus patterns of storm damage. Thus, one panne, which was closest to a tidal channel and had the lowest tidal level, exhibited the largest population frequency and smallest mean frond stature. The highest percent occurrence of gametangia occurred during late summer to early fall when the largest fronds were present. The reproductive pattern in the panne closest to a tidal channel peaked sharply following extensive physical damage to the panne, including diminished depth, enhanced desiccation, and anoxic conditions.
Significance Fossil evidence shows that red algae (Rhodophyta) are one of the most ancient multicellular lineages. Their ecological, evolutionary, and commercial importance notwithstanding, few red algal nuclear genomes have been sequenced. Our analyses of the Porphyra umbilicalis genome provide insights into how this macrophyte thrives in the stressful intertidal zone and into the basis for its nutritional value as human food. Many of the novel traits (e.g., cytoskeletal organization, calcium signaling pathways) we find encoded in the Porphyra genome are extended to other red algal genomes, and our unexpected findings offer a potential explanation for why the red algae are constrained to small stature relative to other multicellular lineages.
As one part of a multi‐institutional project on the biology of Porphyra , we collected extensive population samples of native Porphyra species from Long Island Sound to Nova Scotia. Samples were initially identified to species based on morphological features using taxonomic keys in Bird & McLaughlin (1992). Collections were analyzed using starch gel electrophoresis to look for intra‐specific variation useful in assessing population genetics. Isozyme variation in samples that had been originally identified as Porphyra leucosticta was far greater than expected. Samples from some collections differed by as much as 7 out of 7 loci. Other investigators have used starch gel electrophoresis to reveal cryptic differences in Porphyra that led to the descriptions of new species. In light of our isozyme results, we began a thorough examination of what had been identified as P. leucosticta in the northwestern Atlantic. The study included new collections as well as herbarium specimens. We examined morphology, habitat, seasonality, reproductive patterns, cell size & shape. We also extracted DNA and sequenced 1484bp of the rbc L gene. Based on this evidence, we feel we can circumscribe at least five distinct taxa of Porphyra not previously described from the northwestern Atlantic. Whether these represent new species, or previously described taxa from other geographic regions, we are not yet certain. We present here in detail, descriptions of each species along with summarized results of isozyme and DNA analyses.
The red algal genus Porphyra Roth (Bangiales, Rhodophyta) includes approximately 140 recognized species (Yoshida et al. 1997; Silva 1999). Several recent investigations in diverse geographic regions have resulted in newly described species and/or range extensions, including the North Pacific (Lindstrom and Cole 1990a, 1992a, 1992c; Stiller and Waaland 1993, 1996; Hwang and Lee 1994), North Atlantic (Coll and Cox 1977; Kornmann and Sahling 1991; Brodie and Irvine 1997), South Africa (Griffin et al. 1999) and New Zealand (Nelson et al. 1998; Broom et al. 2002). There appears to be a consensus among the authors of these studies that the genus is understudied and that the number of reported species represents an underestimation of the species present. In the Northwest Atlantic, Bird and McLachlan (1992) indicate “it is becoming apparent that the limits of some species of Porphyra have been too broadly interpreted, and these taxa are in fact ‘form-species’ comprising a number of similar entities.” Very little taxonomic work has been conducted on Porphyra from the Atlantic coast of North America and only eight species have been reported (Schneider and Searles 1991; Bird and McLachlan 1992, Broom et al. 2002): P. amplissima Kjellman, P. miniata (C. Agardh) C. Agardh, P. linearis Greville, P. leucosticta Thuret in LeJolis, P. purpurea (Roth) C. Agardh, P. umbilicalis Kutzing, P. rosengurttii Coll et Cox, and P. suborbiculata Kjellman. Six of the eight species were originally described from Europe in the late 1700’s and 1800’s (Brodie and Irvine in press). In early work by Collins (1900), he lists three species from New England that are Algae Volume 17(4): 203-216, 2002
The red alga Porphyra umbilicalis Kützing has a broad distribution within the North Atlantic. In the Northeast Atlantic, P. umbilicalis is dioecious and reproduces both sexually and asexually, while in the Northwest Atlantic, only asexual reproduction has been observed. In this study, transcriptomes were mined to identify putative single nucleotide polymorphisms (SNP) markers. A computational pipeline was developed that accounts for the specific characteristics of transcriptome dataset, filtered against the available red alga Chondrus genome and P. umbilicalis EST library to eliminate microbial contamination. Five hundred forty-nine putative SNPs were detected within a single population (Schoodic Point, ME, USA). Five of the validated SNP markers were applied in a pilot study of genetic diversity and population structure of seven P. umbilicalis populations within the Gulf of Maine. Results of this study revealed the genetic diversity and structure of P. umbilicalis populations in the Gulf of Maine. Novel genotypes were found in the open coastal populations at Reid State Park, Schoodic Point, and the estuarine tidal rapid population at Wiscasset. Our study represents the first attempt to develop suitable bioinformatic pipeline for RNA-seq to detect SNP markers for red alga Porphyra umbilicalis and successfully used these SNP markers for population study.
Information about past periods of climate change can provide a framework for investigating how marine communities may have adapted to changes both geographically and ecologically. The spatial distribution of variable haplotypes from the nuclear ribosomal DNA internal transcribed spacer (ITS1-5.8S-ITS2) region and a ribosomal DNA group-I intron from the obligate, rocky shore intertidal red alga Porphyra umbilicalis were used to reconstruct its biogeographical history since the last glacial maximum in the North Atlantic. Haplotype distributions from European and North American samples representing the range of P. umbilicalis are consistent with the hypothesis that North American populations were extirpated during the last glacial maximum and subsequently recolonized from European donor populations. A non-coding intergenic region between the mitochondrial cytochrome oxidase (cox)2 and cox3 genes was also investigated, but because there were extremely low levels of intraspecific variation, the spacer was not useful for phylogeographical analysis.
Abstract The intertidal marine red alga Porphyra umbilicalis reproduces asexually in the Northwest Atlantic. We looked for population substructure among typical open-coastal and atypical estuarine habitats in seven asexual populations of P. umbilicalis from Maine to New Hampshire using eight expressed sequence tag-simple sequence repeats (EST-SSR) or microsatellite loci. Six genotypes were identified, four of which may represent recombinant genotypes from a recombination event that took place locally, or that took place prior to introduction to the Northwest Atlantic. Genotypic diversity was lowest in a population from Wiscasset, Maine, which inhabits an atypical habitat high in the intertidal zone of a bridge piling in an estuarine tidal rapid. Genotypic diversity was highest in the southernmost populations from New Hampshire; we identified two genotypes that were unique to the southernmost populations, and probably represent the most derived genotypes. We looked at genetic distances among populations in similar habitats, and found that populations were more closely related to their closest neighboring population than to a population in a similar habitat. We show that genotypic diversity within P. umbilicalis populations in the Gulf of Maine is relatively high and thus fits a model of high steady-state variation within asexual populations.
Intertidal macroalgae are exposed to many abiotic stress factors, and they must regularly react to changes in their environment. We used RNA-seq to describe how Porphyra umbilicalis (Rhodophyta) changes gene expression patterns to interact with different habitats. Tissue samples were taken from a typical habitat along the open-coast of the Northwest Atlantic, as well as from a rare, atypical habitat in an estuarine tidal rapid environment. Differential gene expression analyses suggest that pathogic bacteria and viruses may be a significant factor influencing the transcriptome in the human-impacted estuarine environment, but the atypical habitat does not necessarily induce more stress in Porphyra umbilicalis growing there. We found genes related to nitrogen transport are over-expressed in tissue from the open-coastal site compared to those from the estuarine site, where environmental N levels approach hypertrophic levels. Low N levels impede growth, but high levels are toxic to cells, and we use qPCR to show this species regulates expression of a putative high-affinity NH4+ transporter under low and high N conditions. Differences in expression of this transporter in these habitats appear to be inherited from parent to offspring and have general implications for adaptation to habitat in other species that are capable of asexual reproduction, as well as more specific implications for this species’ use in aquaculture.
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