Rosalina Stancheva

SYSTEMATICS OF THE GENUS ZYGNEMA (ZYGNEMATOPHYCEAE, CHAROPHYTA) FROM CALIFORNIAN WATERSHEDS 1

Natural populations of Zygnema were collected from 80 stream sites across California, and eight species were identified and characterized morphologically. Generic and infrageneric concepts of Zygnema and Zygogonium were tested with cox3 and rbcL gene sequence analysis. Strains of Zygnema were positioned in a single monophyletic clade sister to Zygogonium tunetanum Gauth.‐Lièvre. In both the rbcL and cox3 phylogenies, strains of Zygnema formed two major clades. The first clade contained species that have zygospores with a blue‐colored mesospore or akinetes with a colorless mesospore. The second clade contained species that have a yellow or brown mesospore. The existing taxonomic concepts for Zygnema classification are not consistent with our molecular phylogeny and do not correspond to natural groups. We propose that mesospore color may be useful in the infrageneric classification of Zygnema. Newly described Zygnema aplanosporum sp. nov. and Zygnema californicum sp. nov. have zygospores with a blue mesospore formed in the conjugation tube and separated by a cellulosic sporangial wall. Z. aplanosporum also possessed a combination of vegetative and reproductive features characteristic of Zygogonium, such as presence of short branches, rhizoidal outgrowths, thickened vegetative cell walls, purple‐colored cell content, small compressed‐globular chloroplasts as well as predominant asexual reproduction. Z. aplanosporum and Z. californicum were deeply embedded in a larger clade of Zygnema both in rbcL and cox3 analyses. Based on our observations, there are no features or combination of features that separate Zygnema and Zygogonium. Therefore, we conclude that Zygogonium is probably a synonym of Zygnema.

Investigation of the molecular and morphological variability in Batrachospermum arcuatum (Batrachospermales, Rhodophyta) from geographically distant locations

Vis M.L., Feng J., Chiasson W.B., Xie S.-L., Stancheva R., Entwisle T.J., Chou J.-Y. and Wang W.-L. Investigation of the molecular and morphological variability in Batrachospermum arcuatum (Batrachospermales, Rhodophyta) from geographically distant locations. Phycologia 49: 545–553. DOI: 10.2216/10-04.1 Phylogeographic patterns in Batrachospermum arcuatum were investigated using the mitochondrial intergenic spacer between the cytochrome oxidase subunit 2 and 3 (cox2-3 spacer) from locations worldwide. Sixteen locations were sampled in six regions as follows: three locations in Bulgaria, two in China, three in the northwestern United States, one in New Zealand, six in Hawaii and one in Taiwan. Sequencing of 107 individuals resulted in 12 haplotypes. In the United States and Bulgaria, there was considerable sequence divergence among haplotypes. Likewise in the Hawaiian Islands, there was variation among haplotypes, and each island appeared to have a single haplotype represented. Three closely related haplotypes were present at the Taiwan location. The New Zealand sample was identical to one of the haplotypes from the northwestern United States. Individuals representing the 12 cox2-3 spacer haplotypes were sequenced for the rbcL gene. In the combined analysis, the Hawaii and Taiwan samples were a well-supported clade as were two Bulgaria samples. The US and New Zealand haplotypes formed a well-supported clade and likewise the China samples, but the relationship of the third Bulgaria haplotype to these others was unresolved. The specimens showed morphological variation among localities and regions, but no morphological features appeared to be diagnostic of the molecular results. Batrachospermum arcuatum appears to be a widespread taxon with considerable morphological plasticity that does not coincide with the substantial molecular variation. Alternatively, B. arcuatum may harbour cryptic species. There appears to be a temperate origin of the taxon and a derived group of haplotypes from tropical regions.

Development and comparison of stream indices of biotic integrity using diatoms vs. non-diatom algae vs. a combination

Stream algal indices of biotic integrity (IBIs) are generally based entirely or largely on diatoms, because non-diatom (“soft”) algae can be difficult to quantify and taxonomically challenging, thus calling into question their practicality and cost-effectiveness for use as bioindicators. Little has been published rigorously evaluating the strengths of diatom vs. soft algae-based indices, or how they compare to indices combining these assemblages. Using a set of ranked evaluation criteria, we compare indices of biotic integrity (IBIs) (developed for southern California streams) that incorporate different combinations of algal assemblages. We split a large dataset into independent “calibration” and “validation” subsets, then used the calibration subset to screen candidate metrics with respect to degree of responsiveness to anthropogenic stress, metric score distributions, and signal-to-noise ratio. The highest-performing metrics were combined into a total of 25 IBIs comprising either single-assemblage metrics (based on either diatoms or soft algae, including cyanobacteria) or combinations of metrics representing the two assemblages (for “hybrid IBIs”). Performance of all IBIs was assessed based on: responsiveness to anthropogenic stress (in terms of surrounding land uses and a composite water-chemistry gradient) using the validation data, and evaluated based on signal-to-noise ratio, metric redundancy, and degree of indifference to natural gradients. Hybrid IBIs performed best overall based on our evaluation. Single-assemblage IBIs ranked lower than hybrids vis-à-vis the abovementioned performance attributes, but may be considered appropriate for routine monitoring applications. Trade-offs inherent in the use of the different algal assemblages, and types of IBI, should be taken into consideration when designing an algae-based stream bioassessment program.

Identity and phylogenetic placement of Spirogyra species (Zygnematophyceae, Charophyta) from California streams and elsewhere1

Diversity of the filamentous green algae in the genus Spirogyra (Zygnematophyceae) was investigated from more than 1,200 stream samples from California. We identified 12 species of Spirogyra not previously known for California (CA), including two species new to science, Spirogyra californica sp. nov. and Spirogyra juliana sp. nov. Environmental preferences of the Californian species are discussed in the light of their restricted distribution to stream habitats with contrasting nutrient levels. We also investigated the systematic relationships of Spirogyra species from several continents using the chloroplast‐encoded genes ribulose‐1,5‐bisphosphate carboxylase/hydrogenase large subunit (rbcL) and the beta subunit of the ATP synthase (atpB). Californian species were positioned in most major clades of Spirogyra. The phylogeny of Spirogyra and its taxonomic implications are discussed, such as the benefits of combining structural and molecular data for more accurate and consistent species identification. Considerable infraspecific genetic variation of globally distributed Spirogyra species was observed across continental scales. This finding suggests that structurally similar species from distant regions may be genetically dissimilar and that Spirogyra may contain a large number of cryptic species. Correlating the morphological and genetic variation within the genus will be a major challenge for future researchers.

Phylogenetic position of Zygogonium ericetorum (Zygnematophyceae, Charophyta) from a high alpine habitat and ultrastructural characterization of unusual aplanospores

Zygogonium ericetorum, the type species of the genus, was studied from a natural population collected in Mt. Schönwieskopf, Tyrol, Austria. Generic concepts of Zygogonium and Zygnema were tested with atpB, psbC, and rbcL gene sequence analysis, which showed a sister relationship between Z. ericetorum and Mesotaenium, in an early branching clade sister to a grouping of Zygnema and several other filamentous and unicellular zygnematalean taxa. A variety of light, confocal, transmission electron microscopy, and cytochemical techniques provided new data on the variable chloroplast shape of Z. ericetorum, and its aplanospore structure and development, which has been previously considered taxonomically important but has been ambiguously interpreted. Zygogonium can be distinguished from other zygnematophytes (particularly Zygnema), based on the combination of two characters: (i) irregular, compressed plate‐like chloroplasts and (ii) residual cytoplasmic content left in sporangia outside of the fully developed aplanospores or zygospores. The presence of a sporangial wall that separates the spores from the parent cell should be excluded from the definition of Zygogonium, because it is also observed in Zygnema. Similarly, the ecological characterization of Zygogonium as acidophilic is not unique to the genus. The names of 18 species currently belonging to Zygogonium are here changed to Zygnema, because of incompatibility with this new proposed Zygogonium concept. In the species transferred to Zygnema, chloroplasts are typically stellate in three‐dimensions, and the entire content of fertile cells is transformed into the spore, so there is no cytoplasmic residue.

Discovery of the rare freshwater brown alga Pleurocladia lacustris (Ectocarpales, Phaeophyceae) in California streams

ABSTRACT. Pleurocladia lacustris A. Braun is a freshwater member of the Phaeophyceae, a class of algae that occurs almost entirely in marine waters. It has previously been reported from only about 13 freshwater locations worldwide, just 2 of which are in North America. Outside of North America, P. lacustris has been listed as a threatened species on several European red lists. In this paper, we report the discovery of P. lacustris in 3 calcareous streams draining the Santa Lucia Mountains in coastal California, sites that are more than 1200 km from the nearest known population. Pleurocladia lacustris is a filamentous, benthic species that forms distinctive hemispherical colonies. It co-occurs with the green alga Cladophora glomerata and species of cyanobacteria (Rivularia, Nostoc, Schizothrix spp.). Detailed color illustrations of the diagnostic macroscopic and microscopic features are provided and appear identical to those features of European populations. In the California streams, P. lacustris and other associated algae co-precipitate CaCO3 to form carbonate crusts on rocks. Preliminary ecological data are consistent with other streams and lakes in Europe where P. lacustris has also been reported (pH > 8.0, calcareous substrata, travertine). The global distribution of this presumed rare alga is also described and examined with respect to a specialized ecological niche.

Conjugation morphology of Zygogonium ericetorum (Zygnematophyceae, Charophyta) from a high alpine habitat.

Reproductive characteristics are important for defining taxonomic groups of filamentous Zygnematophyceae, but they have not been fully observed in the genus Zygogonium. Specimens of Z. ericetorum previously studied and used to clarify the generic concept lacked fertile material, which was obtained recently. This study illustrates for the first time, using color light microscopic and fluorescence images, a consequent conjugation stage in Z. ericetorum, including completely developed zygospores and purple cytoplasmic residue content left outside the zygospores, similar to aplanospore formation. Structures confirmed earlier reports and provided new observation informative regarding phylogenetically relevant reproductive characters of Z. ericetorum.

Ochlochaete incrustans sp. nov., a new species of freshwater ulvophycean algae from California, USA, with notes on Friedaea torrenticola

Abstract: During a broad survey of the stream algae of California, a rare and unusual green alga was encountered. Samples were collected in three sites, one 200 m from a stream outlet into the Pacific Ocean and the others 6–20 km inland from the ocean. We initially identified the alga as Friedaea torrenticola Schmidle, which had been previously reported from California by G.M. Smith in 1933. However, additional observations and analysis led us to conclude that the specimen represented a new species of the primarily marine genus Ochlochaete. Ochlochaete incrustans sp. nov. grows in dense, lime-encrusted mats in fast-flowing streams. The thallus is a branched filament terminating in slightly clavate cells. Some intercalary cells are furnished with long, colourless setae. Transmission electron microscopic analysis revealed that the pyrenoid is traversed by a single, straight thylakoid similar to the ulvophycean alga Phaeophila. Molecular phylogenetic analysis of the new species based on the nuclear-encoded 18S rDNA and chloroplast-encoded tufA gene sequences revealed that it is most closely related to Ochlochaete hystrix Thwaites (Ulvaceae, Ulvophyceae).

Morphological variation of the Caloneis schumanniana species complex (Bacillariophyceae) from different environmental conditions in North American streams

Morphological variations of the Caloneis schumanniana (Grunow) Cleve species complex were studied using multivariate analysis. Populations of three species, synonymized in the literature, i.e., C. schumanniana, Caloneis limosa (Kützing) Patrick and Caloneis lewisii Patrick, were analyzed. Their morphological and ecological characteristics were evaluated and outlined for the sampled streams by US EPA’s Western Environmental Monitoring and Assessment Program. Geographic separation among the three taxa was not resolved. This study showed that C. schumanniana has wider ecological tolerance than C. limosa and C. lewisii. Despite the ecological overlap, specific ecological preferences of C. limosa and C. lewisii were described.