Phylogeography of the freshwater red alga Sirodotia (Batrachospermales,Rhodophyta) in Brazil

Considering the lack of knowledge on genetic variation on members of the freshwater red algal of the order Batrachospermales in tropical regions, phylogeographic patterns in Sirodotia populations were investigated using two mitochondrial regions: the cox2‐3 spacer and partial cox1 gene (barcode). Individuals identified as Sirodotia delicatula were analyzed from 14 stream segments across its distribution in Brazil. Phylogenetic analyses based on the ribulose‐1,5‐bisphosphate carboxylase/oxygenase large sub‐unit gene showed three clades, one representing S. delicatula, from all locations in southeastern Brazil and other regions from Brazil. The remaining samples formed two clades, which were highly divergent and distantly positioned from those of S. delicatula: 2.5–2.7% and 3.4–3.7%. This level of variation would warrant the species split of these taxa from mid‐western Brazil. A total of eight cox2‐3 spacer and nine cox1 haplotypes were observed among the 122 individuals studied. One location had two cox2‐3 haplotypes and three locations had two cox1 haplotypes; all others had a single dominant haplotype each. The existence of high intraspecific genetic variation among individuals of distinct locations (several haplotypes), but little variation within a location seems to be a pattern for the Batrachospermales. Haplotype networks showed low variation among the haplotypes from southeastern Brazil (10 locations with divergence of 0.3–1.1% for cox2‐3, 0.1–0.3% for cox1) and high variation among the haplotypes from the mid‐west region (four locations, 4.0–9.3% for cox2‐3, 6.2–8.4% for cox1). Thus, the present data clearly suggest the existence of cryptic species in Sirodotia in Brazil.     

Ecology and morphological characterization of gametophyte and 'Chantransia' stages of Sirodotia huillensis (Batrachospermales, Rhodophyta) from a stream in central Mexico

The morphology and phenology of Sirodotia huillensis was evaluated seasonally in a central Mexican first‐order calcareous stream. Water temperature was constant (24–25°C) and pH circumneutral to alkaline (6.7–7.9), and calcium and sulfates were the dominant ions. The gametophyte stages were characterized by the presence of a distinctive mucilaginous layer, a marked difference in phycocyanin to phycoerythrin ratio between female and male plants, and the presence of a carpogonia with a large trichogyne (>60 µm). Occasionally three capogonia were observed on a single basal cell. The ‘Chantransia’ stages were morphologically similar to those described for the other members of Batrachospermales. A remarkable observation was the formation of dome‐shaped structures, consisting of prostrate filaments that are related with the development of new gametophytes. Chromosome numbers were n = 4 for fascicle cells, cortical filament cells and dome‐shaped cells, and 2n = 8 for gonimoblast filament cells and ‘Chantransia’ stage filaments. Gametophytes and ‘Chantransia’ stages occurred in fast current velocities (60–170 cm/s) and shaded (33.1–121 µmol photons/m²/s) stream segments. The population fluctuated throughout the study period in terms of percentage cover and frequency: the ‘Chantransia’ stages were most abundant in the rainy season, whereas gametophytic plants had the highest frequency values during the dry season. These results were most likely a result of fluctuations in rainfall and related changes in current velocity. Some characteristics of this population can be viewed as probable adaptations to high current velocities: the mucilaginous layer around plants that reduces drag; potential increase in fertilization by the elongate and plentiful trichogynes and abundant dome‐shaped structures producing several gametophytes.     

SYSTEMATIC SIGNIFICANCE OF THE ABSENCE OF PIT-PLUG CAP MEMBRANES IN THE BATRACHOSPERMALES (RHODOPHYTA)1

Four species of the Batrachospermales were examined by transmission electron microscopy to determine whether or not cap membranes, a typical structural component of pit plugs in several orders of red algae, were present. Routine specimen preservation methods used in past studies led to contradictory reports, so Batrachospermum keratophytum Bory, B. sirodotii Skuja ex Reis, Sirodotia suecica Kylin, and S. tenuissima (Collins) Skuja ex Flint were prepared by secondary fixation in potassium permanganate or a combination of potassium ferrocyanide-osmium tetroxide to enhance membrane contrast. These fixation procedures produced clear, well-contrasted images in which cap membranes were absent. The absence of cap membranes in S. suecica and S. tenuissima and the presence of cap membranes in two members of the Nemaliales was confirmed by freeze-substitution methods. Absence of cap membranes in representatives of the Batrachospermales further distinguishes the Batrachospermales from the Nemaliales, the order in which they long resided, and demonstrates the value of this character in elucidating ordinal alliances among the Rhodophyta.     

Phenology of Sirodotia suecica (Batrachospermaceae, Rhodophyta) in a high-altitude stream in central Mexico

The morphology and phenology of a monoecious population of Sirodotia suecica Kylin was evaluated seasonally in a central Mexican fifth-order high-altitude stream. Abundance of gametophytes is positively correlated with concentrations of total dissolved solids, specific conductivity and total ionic concentration; being present the whole dry season and disappearing in the rainy season. The gametophytes grew in eutrophic circumstances and particular microhabitat conditions: high current velocity (66–122 cm s⁻¹), low irradiance (75–263 µmol photons m⁻² s⁻¹) and shallow depth (7–26 cm). Percent cover of gametophytes ranged from 5–90% and significant differences in abundance were not observed when alga was present. Some morphological and reproductive characteristics seem to be adaptations to high current velocity: abundant secondary branches, spermatangia and carpogonia. 'Chantransia' stage, microscopic creeping filaments associated with the base of the gametophyte, were not observed in natural conditions. In terms of reproductive success, the population studied can be regarded as highly efficient, considering the high fertilized carpogonia rate, similar to monoecious populations in lotic habitats. However S. suecica was not common in the study region because it was restricted to particular microhabitat conditions.     

中国连珠藻属(串珠藻科)的分类研究

记述了中国产连珠藻属Sirodotia Kylin的6个种,即黄山连珠藻S.huangshanensis Z．X．Shi et S．L.Xie,威拉连珠藻S．huillensis(Welwitsch ex W．et G．S．West)Skuja,中华连珠藻S.sinica Jao,纤细连珠藻S.delicatula Skuja,瑞典连珠藻S.suecica Kylin和细连珠藻S．tenuissima(Collins)Skuja ex Flint。其中,黄山连珠藻S．huangshanensis Z．X．Shi et S．L.Xie为新种,威拉连珠藻S.huillensis(Welwitsch ex W．et G．S．West)Skuja,纤细连珠藻S．delicatula Skuja和瑞典连珠藻S.suecica Kylin为中国新记录。     

Circumscription of species in the genus Sirodotia (Batrachospermales,Rhodophyta) based on molecular and morphological data

Species level taxonomy and phylogeographical distribution patterns in the freshwater rhodophyte Sirodotia are resolved through phylogenetic inferences based on rbcL and cox2–3 sequence data. Previous studies focused on the taxonomy of specific Sirodotia species or the distributions across a limited geographical region. Our molecular phylogenies included samples attributable to five recognized Sirodotia species and include collections from Australia, Brazil, Costa Rica, Canada, Finland, Mexico, New Zealand, South Africa and the United States. Both rbcL and cox2–3 phylogenies inferred S. suecica, S. tenuissima and S. goebelii as a monophyletic group with little sequence divergence. This result supports the synonymy of S. tenuissima and S. goebelii with S. suecica (the species name with priority). Within this clade, samples collected from Australia and New Zealand formed a monophyletic group with no other discernible phylogeographical patterns within S. suecica. This result seems to be somewhat unusual in the Batrachospermales, as other species have shown greater genetic variation among geographically distant locations. As in previous studies, S. huillensis and S. delicatula were inferred as a separate species based on the rbcL phylogeny, supporting the current taxonomy. A specimen of S. aff. huillensis from South Africa, may represent a new species but further research is necessary before it can be designated as such.     

我国淡水红藻两新记录种

本文报道我国淡水红藻的两个新记录种,即弧形串珠藻Batrachospermum arcuatum Kylin emend.Vis et al.和细链珠藻Sirodotia tenuissima(Collins) Skuja ex Flint.标本均采自我国山西省。       

DISTRIBUTION AND SYSTEMATICS OF THE FRESHWATER GENUS SIRODOTIA(BATRACHOSPERMALES,RHODOPHYTA) IN NORTH AMERICA1

Multivariate morphometrics and image analysis were used to determine the number of well-delineated infrageneric taxa of Sirodotia in North America. Three groupings were distinguished from 25 populations examined from Newfoundland and Quebec in the north to central Mexico in the south. These groupings were statistically related to 10 type specimens, and the following species were recognized: Sirodotia huillensis (Welwitsch ex W. et G. S. West) Skuja (syn. S. ateleia Skuja), S. suecica Kylin (syn. S. acuminata Skuja ex Flint and S. fennica Skuja), and S. tenuissima (Collins) Skuja ex Flint. These species are differentiated on the basis of whorl shape and degree of separation at maturity (S. suecica, rounded and appressed; S. huillensis and S. tenuissima, truncated apex and separated), the density of spermatangia (S. huillensis, dense clusters; S. suecica and S. tenuissima, sparsely aggregated), and the mode of germination of the gonimoblast initial (S. suecica and S. tenuissima, from the nonprotuberant side of the fertilized carpogonium; S. huillensis from the protuberant side). Sirodotia huillensis was found only in the desert-chaparral, whereas S. suecica and S. tenuissima occurred from south-temperate to boreal regions in cool (temperature 8–18° C), low ion (specific conductance 10–99 μS · cm^?1), and mildly acidic to neutral (pH 5.7–7.3) waters.