Ulva and Enteromorpha are two of the most common, ubiquitous, and environmentally important genera of green seaweeds. They are widely regarded as easily distinguishable because of their dramatically different morphologies: Ulva species are flat, lettucelike blades two cell layers thick, and Enteromorpha species form hollow liquid- or gas-filled tubes one cell thick, which may also be highly branched. We present molecular phylogenetic analyses of nuclear ribosomal RNA ITS sequences from 39 samples representing 21 purported species within these two genera. The results clearly indicate that the two genera are not respectively monophyletic and that the characteristic Ulva and Enteromorpha morphologies have arisen independently several times throughout the evolutionary diversification of the group. The analyses demonstrate that this radical change in gross morphology can also happen within clades exhibiting sequence divergence typical of conspecific assemblages of this group. We suggest that this morphological flexibility is the result of some form of developmental switch that results in either blades or tubes, but that this putative switch must be activated relatively infrequently, since there is evidence that some lineages have retained their form for significant periods. This discovery suggests a possible new model system for study of the molecular mechanisms involved in the interplay between environmental stimuli and plant development.
We report six complete 18S ribosomal DNA (rDNA) sequences representing five brown algal orders: Sporochnus comosus C. A. Agardh (Sporochnales), Chorda tomentosa Lyngbye (Chordaceae, Laminariales), Saccorhiza polyschides (Lightfoot) Batters (Phyllariaceae, Laminariales), Desmarestia ligulata (Lightfoot) Lamouroux (Desmarestiales), Ectocarpus siliculosus (Dillwyn) Lyngbye (Ectocarpales), and Scytosiphon lomentaria (Lyngbye) J. G. Agardh (Scytosiphonales). These sequences were compared with published laminarialean (Alaria marginata Postel et Ruprecht [Alariaceae] and Macrocystis integrifolia Bory [Lessoniaceae]) and fucalean (Fucus gardneri Silva) rDNA sequences for phylogeny inference using both the distance‐matrix and parsimony methods. The inferred 18S phylogenies clustered Sporochnus, Desmarestia, Chorda, Saccorhiza, Alaria, and Macrocystis in an assemblage. This Sporochnales–Desmarestiales–Laminariales (S‐D‐L) complex was consistently separated from the Ectocarpales, Scytosiphonales, and Fucales by bootstrap analyses. The inferred phylogenies are consistent with several possible evolutionary processes leading to this S‐D‐L complex. Members in this assemblage lack eyespots in their sperm, and their sperm have the atypical brown algal flagellation: shorter anterior and longer posterior flagella. In addition, they are oogamous with a heteromorphic alternation of generations between a microscopic gametophyte and a macroscopic sporophyte. Members of the S‐D‐L complex can be separated into different phylogenetic lines based on the presence/absence of eyespots in their meiospores. Our findings support the contention that the Sporochnales, Desmarestiales, and Laminariales are closely related. In addition, our rDNA tree suggests that the Laminariales is paraphyletic.
Newly adapted extraction methods for harvesting total cellular DNA from kelp (Laminariales; Phaeophyta) exploit the life‐history stages of these heteromorphic algae. Earlier techniques, developed primarily for chloroplast DNA extraction, were time consuming and labor intensive and required large quantities of fresh sporophyte tissue. In contrast, the new methods expedite DNA extraction by employing dried sporophyte laminae or fresh gametophyte filaments and meiospores. The current methods require less tissue and procedural manipulation, reducing the time and labor involved in DNA extraction. Additionally, the current methods were successfully employed to extract DNA from herbarium specimens up to 22 years old. Total cellular DNA yields were 12.8 and 26.4 μg:g−1 from dried laminae,: 1.9 and 11 μg from small volumes of concentrated gametophyte filaments (25 μL), and 43 to 54.5 μg from pellets of isolated meiospores (50 μL). Following purification on Sepharose columns, DNA from all three sources was sufficiently pure for molecular applications, including restriction endonuclease digestion, Southern blot‐hybridizations, and amplification via the polymerase chain reaction.
Partial 18S rRNA gene sequences have been determined for thirteen brown algae representing nine Northeast Pacific brown algal orders: Chordariales, Desmarestiales, Dictyosiphonales, Dictyotales, Ectocarpales, Fucales, Scytosiphonales, Sphacelariales and Syringodermatales. These sequences were compared with published sequences from a kelp (Laminariales), a xanthophyte and a bacillariophyte. A preliminary phylogeny generated by the neighbor-joining phylogeny inference method indicated that the class Phaeophyceae is a monophyletic group in relation to the xanthophyte and the bacillariophyte. Further, bootstrap analysis of the phylogeny consistently grouped together all the representatives belonging to the orders Ectocarpales, Chordariales, Dictyosiphonales and Scytosiphonales and separated them from the representatives belonging to the other brown algal orders. These results offer valuable insights into the controversial brown algal orders' phylogeny and provide additional data to the phylogenetic relationship study among the chromophyte classes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.