Robert G. Sheath

Ribosomal DNA phylogeny of the Bangiophycidae (Rhodophyta) and the origin of secondary plastids

We sequenced the nuclear small subunit ribosomal DNA coding region from 20 members of the Bangiophycidae and from two members of the Florideophycidae to gain insights into red algal evolution. A combined alignment of nuclear and plastid small subunit rDNA and a data set of Rubisco protein sequences were also studied to complement the understanding of bangiophyte phylogeny and to address red algal secondary symbiosis. Our results are consistent with a monophyletic origin of the Florideophycidae, which form a sister-group to the Bangiales. Bangiales monophyly is strongly supported, although Porphyra is polyphyletic within Bangia. Bangiophycidae orders such as the Porphyridiales are distributed over three independent red algal lineages. The Compsopogonales sensu stricto, consisting of two freshwater families, Compsopogonaceae and Boldiaceae, forms a well-supported monophyletic grouping. The single taxon within the Rhodochaetales, Rhodochaete parvula, is positioned within a cluster containing members of the Erythropeltidales. Analyses of Rubisco sequences show that the plastids of the heterokonts are most closely related to members of the Cyanidiales and are not directly related to cryptophyte and haptophyte plastid genomes. Our results support the independent origins of these secondary algal plastids from different members of the Bangiophycidae.

PHYLOGENY OF THE BATRACHOSPERMALES (RHODOPHYTA) INFERRED FROM rbcL AND 18S RIBOSOMAL DNA GENE SEQUENCES

The sequence data from the large subunit of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (rbcL) gene and 18S ribosomal DNA (small subunit) of taxa in the freshwater rhodophyte order Batrachospermales were used to construct phylogenetic hypotheses. Taxa examined in this study represent four families, eight genera, and six sections of the genus Batrachospermum. In addition, Rhododraparnaldia oregonica Sheath, Whittick et Cole, was included in the analysis because it shares particular ultrastructural, reproductive, and morphological characteristics with members of the Batrachospermales and Acrochaetiales. The trees generated from each gene, as well as a combined data set, were largely congruent. Rhododraparnaldia consistently occurs on an early branch within the Acrochaetiales–Palmariales clade and does not appear to be a member of the Batrachospermales. In addition,Thorea violacea Bory de St. Vincent was not closely related to the other taxa of the Batrachospermales in all trees and hence the family Thoreaceae does not appear to be a natural grouping within this order. All other taxa analyzed, which are presently classified within this order, formed a monophyletic clade in most analyses. Psilosiphon scoparium Entwisle was not closely allied with the taxa of the Lemaneaceae, lending support to the newly proposed family Psilosiphonaceae. Sequence data from the remaining taxa of the Lemaneaceae support the concept of a derived monophyletic clade. The genus Batrachospermum appears to comprise many morphologically similar but distantly related taxa, which will need further investigation to resolve their taxonomic status. Tuomeya, Sirodotia and Nothocladus are retained at the generic level until further data are obtained.

Tundra stream macroalgae of North America: composition, distribution and physiological adaptations

Eighty-three infrageneric taxa of stream macroalgae have been reported from tundra regions of North America, composed of 32 cyanobacteria, 35 Chlorophyta, 10 Chrysophyta and 6 Rhodophyta. There are few if any endemics represented in this flora. The most widespread species are the cyanobacteria Rivularia minutula, Nostoc commune and Tolypothrix tenuis as well as asexual populations of the chlorophyte genus Zygnema. The relative contribution of cyanobacteria compared to that of the Chlorophyta increases from the low to high arctic. Number of species per segment ranges from 0 to 7, with a mean of 2.8, and varies little between the low and high arctic. The percentage of stream bottom covered by macroalgae ranges from 0 to ca. 75%; mean cover values for low and high arctic streams are ca. 12 and 8%, respectively. Tundra macroalgae tend to be more abundant and diverse in less rigorously flowing stream sections. Most species tolerate prolonged freezing by forming resistant vegetative cells with thick walls, plentiful reserves and low molecular weight solutes to lower the freezing point. Many tundra stream macroalgae also produce ‘sunscreen’ pigments to reduce exposure to damaging radiation in the blue and ultraviolet regions. Nutrients tend to be low and phosphorus is often limiting in these systems. Arctic streams appear to differ from those of Antarctica in having potential grazers of macroalgae, such as the chironomid Diamesa, the mayfly Baetis and the caddisfly Brachycentrus.

BIOGEOGRAPHYOF BATRACHOSPERMUM GELATINOSUM (BATRACHOSPERMALES, RHODOPHYTA) IN NORTH AMERICA BASED ON MOLECULAR AND MORPHOLOGICAL DATA1

Fifteen populations of the widespread fieshwater red alga Batrachospermum gelatinosum (L.) De Candolle were sampled throughout the geographic range in North America from central Alabama, U.S.A. (33° N), to Ellesmere Island, Northwest Territories (NWT), Canada (80° N). Analysis of ribosomal DNA internal transcribed spacer (ITS) 1 and 2 sequences yielded a parsimony tree with a large polytomy consisting of most populations plus a branch with one Nova Scotia and two NWT populations. The nucleotide variation, both within the polytomy and within the branch, was small (< 1%). The sequence divergence between the branch and polytomy was 3%. The lengths of the ITS 1 and 2 sequences of B. gelatinosum, 216–229 and 448–458 base pairs, respectively, fall within the very broad ranges reported for other red algae. The cluster analysis of 11 morphometric characteristics revealed three groupings of populations, partly based on geographic distribution. All tundra, eastern boreal forest, and mid‐western hemlock‐hardwood populations were in one grouping, whereas the deciduous forest, coastal plain, and eastern hemlock‐hardwood populations were in a second. How ever, one deciduous forest population from Rhode Island, U.S.A. was unassociated. There was considerable overlap in morphometric characteristics among the three groupings. Based on this fact and the relatively small nucleotade variation in ITS sequences, we conclude that B. gelatinosum is a morphologically variable and geographically widespread species that is a valid taxonomic entity.

Seasonality of macroalgae and epilithic diatoms in spring-fed streams in Texas, USA

A seasonal study of two spring-fed stream systems in south-central Texas was undertaken over a 15-month period from June 1996 to September 1997. Relative abundance of the epilithic diatom flora, percent cover of macroalgae, and several physical and chemical conditions were monitored in one 20-m stretch in each of the streams at approximately two-month intervals. Six additional spring-fed stream segments were sampled in May 1996 for macroalgae and measured for the same conditions, in order to determine how representative the macroalgal floras of the study sites were of south-central and western Texas. Conditions in the two stream segments were relatively constant over the 15 months, except for maximum depth; this finding is similar those reported for other spring-fed systems worldwide. Sixty-eight diatom taxa and nine macroalgae taxa were identified from the San Marcos River, which compares to 46 diatom taxa and six macroalgae taxa from the Comal River. Several diatom and macroalgae species were significantly correlated to stream conditions (e.g. Dichotomosiphon tuberosus and Hildenbrandia angolensis with daylength, and Amphora pediculus with maximum depth). Twenty-one macroalgal taxa were identified from the six additional spring-fed steam segments. Conditions in these streams were very similar to those measured in the San Marcos River and Comal River, except that they had a higher average pH x= 8.1 versus x= 7.6). The epilithic diatom flora of the San Marcos River and the Comal River contains many of the diatom and some macroalgal taxa commonly reported from springs globally.

A re‐examination of the morphology, ultrastructure and classification of genera in the Lemaneaceae (Batrachospermales, Rhodophyta)

Vegetative and reproductive morphology and ultrastructure were examined for the three genera of the freshwater red algal family Lemaneaceae: Lemanea (two species, seven populations), Paralemanea (two species, three populations) and Psilosiphon (one species, one population). Psilosiphon is readily distinguished from the other two genera in having an outer cortex composed of well‐defined filaments interconnected with a dense medulla (both cell types being little vacuolated), spores cleaving off obliquely, putative spermatangia scattered on the thallus surface and reproduction by adventitious filaments. Based on the distinctness of this genus (and corroborated by molecular phylogenies in preparation), a new family is described, the Psilosiphonaceae. Lemanea and Paralemanea appear to be closely related, with an outer cortex that has cells of increasing size and vacuolation from the periphery to the interior and not in obvious rows, a central lumen that contains few ray cells but no medullary filaments, sexual reproduction with spermatangia in distinct clusters, and carpospores in chains, some of which can germinate in the thallus lumen. Lemanea and Paralemanea have distinguishing characteristics that the other genus does not: for Lemanea, hair cells, ray cells abutting the outer cortex and spermatangia in patches; for Paralemanea, no hair cells or ray cells appressed to the outer cortex, inner cortical filaments surrounding the central axis and spermatangia in rings.

Seasonality and distribution of epilithic diatoms, macroalgae and macrophytes in a spring-fed stream system in Ontario, Canada

A study of the epilithic diatom, macroalgal and macrophyte communities from a spring-fed stream in Ontario, Canada was undertaken from September 1996 to July 1997. The relative abundance of the epilithic diatom flora, percent cover of macroalgal and macrophyte taxa, and several physical and chemical stream conditions were monitored along a 20-m stretch at each of four sites, approximately every 2 months. Several stream conditions were relatively constant over the sampling period (pH, maximum width and maximum depth), while others exhibited a distinct seasonal pattern (water temperature, specific conductance and daylength) and some fluctuated strongly with no discernable seasonal pattern (turbidity, current velocity). A total of 124 taxa were identified from the four sites, including 79 epilithic diatoms, three macroalgal diatom species (large gelatinous masses), one cyanobacterium, two red algae, eight green algae, one chrysophyte alga, one tribophyte alga, three mosses, three horsetails and 23 angiosperm taxa. Species richness was positively correlated to stream channel maximum width and depth, indicating that the total number of species tends to increase in a downstream direction. Distribution of several diatom and macroalgal species was significantly correlated to stream conditions (e.g. Gomphonema parvulum and Phormidium subfuscum with current velocity); however, the vast majority of species did not display seasonal variation in abundance that could be explained by changes in stream conditions. Many of the taxa identified from Blue Springs Creek are common elsewhere in North America.

Biogeography and systematics of Hildenbrandia (Rhodophyta, Hildenbrandiales) in Europe: inferences from morphometrics and rbcL and 18S rRNA gene sequence analyses

Twenty-one marine and freshwater specimens of Hildenbrandia from Europe were compared by analyses of morphometric data and sequences of the rbcL chloroplast gene (which codes for the large subunit of the ribulose-1,5-bisphosphate carboxylase/oxygenase enzyme) and the nuclear 18S ribosomal RNA (rRNA) gene. Eleven freshwater specimens, all corresponding to H. rivularis, were collected from the British Isles, Germany, France, Austria, Spain and Italy. Six marine specimens, representing H. rubra, were obtained from Northern Ireland, Wales, France, Norway, Sweden and the Netherlands, while four marine specimens, corresponding to H. crouanii, were collected from Scotland and Germany. Morphometric analyses of vegetative and reproductive characters distinguished three groups of specimens, which correspond to the three species. Parsimony and distance analyses of the rbcL and 18S rRNA genes were performed on these samples and sequences of North American representatives were included to determine their inter-relationships. The rbcL gene sequence analyses separated the marine and freshwater specimens, with the H. rivularis and H. angolensis representatives forming a wellsupported monophyletic clade. The rbcL sequence analyses did not resolve the groupings of marine specimens determined in the morphometric analysis. Analyses of the 18S rRNA gene sequences also supported separation of the marine samples from freshwater samples, although the bootstrap and decay support was not as strong as for the rbcL gene. H. rubra formed a monophyletic clade that was weakly supported. In terms of biogeographic trends, the fairly low intraspecific divergence of H. rivularis (0–1·9% for the rbcL gene and 0–3·6% for the 18S rRNA gene) and the positioning of these samples in the gene trees supports the concept that they are derived from marine populations.

SYSTEMATIC STATUS AND PHYLOGENETIC RELATIONSHIPS OF THE FRESHWATER GENUS BALBIANIA (RHODOPHYTA)

The freshwater rhodophyte Balbiania investiens (Lenormand) Sirodot was collected as an epiphyte of Batrachospermum in small streams in England, Ireland, and Germany. Unialgal cultures and field collections of Balbiania were analyzed in terms of their morphology, ultrastructure, and the DNA sequences of the genes coding for the large subunit of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (rbcL) and 18S ribosomal RNA (rRNA), as well as the first internal transcribed spacer region (ITS1) of the rRNA genes. One of the major distinguishing features of this genus is the production of spermatangia on the tips of specialized, elongate cells. The spermatangia are cut off in a cluster together with similar nonspermatangial cells that are packed with starch granules. The only other rhodophyte genus with this feature is Rhododraparnaldia; the two genera are differentiated from each other by the pattern of branching, substratum of attachment, and type of diploid phase. In the parsimony and distance trees inferred from the two gene sequences as well as in a combined parsimony tree, Balbiania and Rhododraparnaldia grouped together on a well‐supported branch separate from other taxa of the Batrachospermales, Acrochaetiales, Nemaliales, and Palmariales. However, the two genera are positioned within a clade containing the last three orders. Based on these findings, it is clear that the genus Balbiania is a valid taxon and that it is phylogenetically associated with Rhododraparnaldia. A new order is proposed, the Balbianiales. The two specimens of Balbiania analyzed from England and Germany have identical sequences for all regions of DNA analyzed.

A molecular and morphological investigation of the relationship between Batrachospermum spermatoinvolucrum and B. gelatinosum (Batrachospermales, Rhodophyta)

Four populations of the newly described freshwater red algal species Batrachospermum spermatoinvolucrum were sampled from British Columbia on the west coast of North America and Labrador on the east. The rDNA internal transcribed spacer (ITS) 1 and 2 sequences, RUBISCO large subunit (rbcL) gene data for three of the populations and morphometric characteristics were compared with those of B. gelatinosum. In addition, the key feature distinguishing B. spermatoinvolucrum, spermatangia on the involucral filaments of the carpogonial branch, was investigated seasonally in one British Columbia population of this species. The ITS analysis suggested that the B. spermatoinvolucrum populations were more closely related to particular B. gelatinosum populations than to each other and did not form a monophyletic clade. Two populations of B. spermatoinvolucrum from Labrador and British Columbia had identical rbcL sequences that were distinct from that of B. gelatinosum. However, the rbcL sequence from the third populati...