Upright Fronds Research Articles

Phylogenetic relationships among the Rangeomorpha: the importance of outgroup selection and implications for their diversification

The Rangeomorpha are the oldest, most diverse, and most disparate clade of Ediacaran macrofossils. Easily identifiable by their self-similar branching pattern, they occupied epibenthic niche space ranging from the lowest-tiered and recumbent taxa up to metre-long upright fronds. A phylogenetic analysis using the largest and most complete character set known for this group scored for 14 separate taxa was undertaken to resolve their internal relationships and test previous hypotheses of their evolutionary and ecological history. Owing to the lack of consensus on the relationship amongst Ediacaran clades, several permutations with different potential outgroup taxa were performed. Across these analyses, there is a strong signal for an upright frondose ancestral state for this clade, likely displaying primary branches that were double-sided, nonrotated, with the lower-tiered and recumbent forms being derived members of a single subclade. This has implications on the life history reconstruction as well as taxonomic implications for this clade and the origins of large multicellular life in the late Ediacaran.

Evolutionary reversals in Bossiella (Corallinales, Rhodophyta): first report of a coralline genus with both geniculate and nongeniculate species.

This is the first report of a coralline genus with both geniculate (upright fronds with non-calcified joints) and nongeniculate species that has been verified by DNA sequence data. Two nongeniculate (crustose) species of Bossiella are recognized, B.mayae sp. nov. and B.exarticulata sp. nov. DNA sequencing of the lectotype specimen of Pseudolithophyllum whidbeyense revealed that this name had been misapplied and instead belongs to an undescribed coralline species in the Hapalidiales. Phylogenetic analyses of concatenated DNA sequences (psbA, rbcL, COI-5P) indicate that B.mayae and B.exarticulata represent phenotypic reversals from the geniculate character state back to the nongeniculate character state. Secondary loss of genicula has occurred three times in the subfamily Corallinoideae, once to generate the entirely nongeniculate genus Crusticorallina and twice in the now morphologically heterotypic Bossiella. Since phenotypic reversals have occurred several times during the evolution of coralline algae, we speculate about the putative mechanism and adaptive significance of this phenomenon.

Upright Fronds of Dryopteris intermedia Suffer Frost Damage and Breakage during Winter

The most abundant fern species in northeast United States forests are wintergreen. These ferns keep their fronds for one year before replacing them in the spring. The wintergreen fronds soften at their base in fall and survive the winter under snow, allowing vernal photosynthesis and providing an energetic benefit to the plant. This study addressed whether or not the softening of the stipe is critical to the evolutionary adaptiveness of the wintergreen leaf habit. I kept the fronds of 12 Dryopteris intermedia plants upright through the winter of 2015–2016 and left those of 12 other plants prostrate as controls. In the spring of 2016, a greater proportion of the frond surface area had frost damage on the upright fronds than on the control plants, and a greater proportion of the fronds were broken in the upright plants than in the control plants. The softening of the stipe was probably a critical step in the evolution of the wintergreen habit in D. intermedia.

Spatial distribution and reproductive phenology of sexual and asexual Mastocarpus papillatus (Rhodophyta)

Fierst J.L., Kübler J.E. and Dudgeon S.R. 2010. Spatial distribution and reproductive phenology of sexual and asexual Mastocarpus papillatus (Rhodophyta). Phycologia 49: 274–282. DOI: 10.2216/09-41.1Species of the genus Mastocarpus exhibit two distinct life cycles, a sexual alternation of generations and an obligate, asexual direct life cycle that produces only female upright fronds. In the intertidal red alga, M. papillatus (Kützing) sexual fronds dominate southern populations and asexual fronds dominate northern populations along the northeast Pacific coast, a pattern of spatial separation called geographic parthenogenesis. Along the central coast of California, sexual and asexual variants occur in mixed populations, but it is not known whether they are spatially separated within the intertidal zone at a given site. We investigated reproductive phenologies and analyzed patterns of spatial distributions of sexual and asexual M. papillatus at three sites in this region. Sexual M. papillatus were aggregated lower on the shore at two sites and only reproduced during part of a year, while asexual M. papillatus occurred throughout the intertidal range at all sites and reproduced throughout the year. The distribution patterns of sexual and asexual M. papillatus are consistent with a hypothesis of shoreline topography influencing their dynamics of dispersal and colonization. Spatial and temporal partitioning may contribute to the long-term coexistence of sexual and asexual life histories in this, and other, species of Mastocarpus. The occurrence of geographic parthenogenesis at multiple spatial scales in M. papillatus provides an opportunity to gain insight into the phenomenon.

Life History and Systematic Studies of Pseudothrix borealis gen. et sp. nov. (=North Pacific Capsosiphon groenlandicus, Ulotrichaceae, Chlorophyta)

We cultured a tubular marine green alga, originally identified as Capsosiphon groenlandicus (J. Agardh) K.L. Vinogradova, from Amaknak Island, Alaska. The alga had an alternation of heteromorphic generations in which tubular monoecious fronds produced quadriflagellate zoospores and/or biflagellate isogametes. The gametes fused to produce cysts or Codiolum-like zygotes with long, tortuous stalks. Cysts and codiola produced 8-16 aplanospores, which germinated in situ to yield upright fronds. Fronds arising from both aplanospores and zoospores displayed a distinctive development in which non-septate colorless rhizoids from the base of the initially uniseriate, Ulothrix-like filament were transformed into septate uniseriate Ulothrix-like photosynthetic filaments. These transformed filaments then developed new basal non-septate rhizoids. This pattern of rhizoids becoming filaments, which then produced new rhizoids, was repeated to yield a tuft of up to 50 fronds. Periclinal and longitudinal divisions occurred in each filament, starting basally, until the mature tubular thallus was achieved. Pyrenoid ultrastructure revealed several short inward extensions of chloroplast lamellae, each of which was surrounded by pyrenoglobuli. Analysis of ribosomal SSU and ITS sequences placed this alga in the family Ulotrichaceae, order Ulotrichales, together with but as a distinct species from North Atlantic Capsosiphon groenlandicus. Analysis of a partial ITS sequence from authentic Capsosiphon fulvescens, the current name of the type of the genus Capsosiphon, indicated that neither our material nor C. groenlandicus belongs in that genus, and we propose a new genus, Pseudothrix, to accommodate both species. We propose P. borealis for the North Pacific entity formerly called C. groenlandicus and make the new combination P. groenlandica for the Atlantic species.

New phenomenon in early development of sporelings inGracilaria asiatica Chang et Xia (Gracilariaceae, Rhodophyta)

Study on the early development of sporelings from carpospores ofGracilaria asiatica Chang et Xia was conducted indoors under controlled culture conditions. Besides normal development of sporelings, a new developmental phenomenon of filamentous frond was observed. It was composed of one or two rows of cells, and took place from the outmost brim of the basal disc. During the early disc stage of germinated carpospores, one or two filamentous fronds formed on about 10% basal discs. Simultaneously, young fronds began to arch slightly from the centers of single and coalescent discs; lately more filamentous fronds up to 80% appeared on the brims of basal discs. Meanwhile one or more upright fronds protuberated on the basal discs. Generally, filamentous fronds exhibited in self-existence or co-existence forms with normal young sporelings on the same basal disc, and single cell detached from filamentous fronds developed into a new filamentous frond. This new phenomenon exhibited a unique differentiation pathway during the early development ofG. asiatica, which would be potential for the application in artificial sporelings nursery.

Spatial and Temporal Distribution of Life History Variants in the Red Alga, Mastocarpus Papillatus

AbstractWe investigated small‐scale spatial structure in Mastocarpus papillatus, a red alga with sexual and apomictic life‐history variants. Spatial structure and habitat partitioning can facilitate the coexistence of ecologically similar organisms, and in M. papillatus a large scale geographic spatial division is well documented. Variants of M. papillatus display geographic parthenogenesis where sexual fronds are common south of San Francisco Bay and apomicts dominate north of San Francisco Bay. Although geographic parthenogenesis in M. papillatus is well‐documented small‐scale spatial structure was not previously known due to the similar appearance of sexual and apomictic upright fronds. We investigated whether sexual and apomictic fronds differed in their spatial distribution by sampling for vertical differences in intertidal height and horizontal patchiness. Fronds were sampled when reproductive and cultured for life history. We found sexual variants were significantly aggregated at lower intertidal heights while apomicts were found throughout the intertidal range. Sexual fronds were strongly seasonal and reproduced October–December whereas apomictic fronds reproduced throughout the year. These results parallel the large‐scale geographic distribution with apomicts inhabiting marginal areas, and suggest dispersal capability may also facilitate geographic parthenogenesis.

COEXISTENCE OF SIMILAR SPECIES IN A SPACE-LIMITED INTERTIDAL ZONE

The lower intertidal zone (0.0 to +1.0 m mean low water [MLW]) of rocky shores in New England is a space-limited community occupied by two similar rhodophyte seaweeds, Chondrus crispus and Mastocarpus stellatus, that overlap broadly in their use of three essential resources: space, light, and nutrients. C. crispus coexists primarily with the prostrate-crust generation of M. stellatus lower on the shore (less than +0.35 m MLW) and with the alternate upright-frond generation higher on the shore (greater than +0.35 m MLW). Our objectives were to determine (1) whether these two species compete and (2) if so, what process(es) enable their coexistence. Upright fronds of M. stellatus transplanted to the lowest intertidal zone (less than +0.25 m MLW) where C. crispus predominates grew faster and showed higher survivorship after 2 yr than those transplanted to areas where M. stellatus predominates. However, the failure of upright fronds of M. stellatus to consistently recruit limits their abundance in the lowest z...

The phenology of leaf life spans in woodland populations of the ferns Dryopteris filix-mas (L.) Schott and D. dilatata (Hoffm.) A. Gray in Derbyshire

WILLMOT, A., 1989. The phenology of leaf life spans in woodland populations of the ferns Dryopteris filix-mas (L.) Schott and D. dilatata (Hoffm.) A. Gray in Derbyshire. The results of a survey on the number of upright fronds per plant in a population of Dryopteris filix-mas and in a population of D. dilatata over a 14 month period are presented. These coupled with similar information on the number of developing fronds per plant demonstrate that large plants in the population of each species were summergreen, while small ones were wintergreen. This size-specific difference in leaf phenology does not seem to have been recorded before in Dryopteris filix-mas. It is suggested that this difference, in both species, may have been due to either the different environments in which the plants grew or to a risk-sensitive strategy in the small plants. It is considered that such a strategy might be concerned with the obtaining or retention of resources at a critical period in the life history of the species.

A field study on the growth and development ofDumontia contorta

Young, crustose plants ofDumontia contorta grown in the laboratory from carpospores were transferred in September 1983 to their natural habitat in Lake Grevelingen (SW Netherlands). The number of upright fronds per crust, length of upright fronds, and diameter of crusts were determined monthly until October 1984 and the presence of tetrasporangia was noted. Although fronds were initiated from crusts throughout the period of short daylengths (<13 h light per day, i.e. from September to March), the majority of the fronds was initiated in October and November when short daylengths coincided with optimum temperatures for frond initiation (ca 10–20°C). By April, i.e. within 5–6 months, these plants had reached maximum sizes and had become fertile; subsequently, the plants decayed. The successively smaller numbers of fronds that were formed in December and January also reached maximum sizes after ca 5–6 months, i.e. by May and June, but these fronds remained much smaller than the fronds initiated in October–November, possibly because of lower temperatures and light levels at the start of their growth. It is suggested that the fronds have a fixed maturation period (ca 5–6 months) irrespective of their size and the moment of their initiation. Crusts were shown to “oversummer” and to produce new fronds at the onset of shortday conditions in September 1984.

Palmaria mollis stat. nov.: a newly recognized species of Palmaria (Rhodophyceae) from the northeast Pacific Ocean

Attempts were made to hybridize Palmaria palmata (L.) O. Kuntze from the North Atlantic Ocean with Palmaria palmata f. mollis (Setchell and Gardner) Guiry from the eastern North Pacific Ocean. No hybrids were obtained in reciprocal crosses, although fertilization was readily achieved for control crosses within each taxon. The number and placement of carpogonia on well-developed female gametophytes (disc diameter, 100–150 μm) was different for the two taxa. The Atlantic plants had comparatively few carpogonia (1–10), which were always found at the center of the holdfast disc or on young upright fronds, whereas the Pacific plants had many carpogonia (15–60), which were most commonly located away from the centermost portion of the disc and were never observed on developing fronds. The two taxa also differed in their susceptibility to a small parasitic Oomycete of the genus Petersenia Sparrow, which is pathogenic for f. mollis but did not infect the Atlantic plants. Cytological examination revealed that f. mollis has n = 21 chromosomes, the same as P. palmata from the north Atlantic Ocean. In view of the genetic isolation between the two forms, P. palmata f. mollis is raised to specific status as Palmaria mollis (Setchell &amp; Gardner) van der Meer &amp; Bird.

Search for possible latitudinal ecotypes inDumontia contorta (Rhodophyta)

Effects of daylength and temperature on the formation of erect fronds (macrothalli) from crusts (microthalli) ofDumontia contorta (S. G. Gmel.) Rupr. from three localities in Nova Scotia and one locality in Southern Iceland were investigated and compared to such effects shown by strains from three different East Atlantic localities (Isle of Man; Zeeland, S. W. Netherlands; and Roscoff, Brittany, France). Although these strains showed small differences in their temperature-daylength responses, these could not be interpreted as latitudinal adaptations, and consequently no latitudinal ecotypes could be found forDumontia contorta in the N. Atlantic Ocean. Upright fronds are formed at a broad temperature range of about 4°–18°C and at daylengths ≤ 13 h. Only in the southernmost part of its distribution area can high autumnal temperatures be expected to block the reappearance of upright fronds after passage of the critical daylength in September. In the larger part of the distribution area even summer temperatures are not high enough to block formation of uprights and here apparently only short daylengths initiate the reappearance of young upright fronds in autumn. The consequences of these aspects of the life history regulation for the geographic distribution are discussed.

Morphology, Phenology and Photoperiodism in Halymenia latifolia Kütz. (Rhodophyta) from Ireland

Halymenia latifolia Crouan frat. m Uoyd ex Kutzing (Cryptonemiales, Halymeniaceae), a marine red alga originally described from the Brittany coast, has been positively identified for the first time in the British Isles, growing in the subtidaJ at two sites in Galway Bay, western Ireland. Plants grow only on dead maerl (unattached coralune algae) and Shell fragments. Acrochaetioid filaments form the basal holdfast and these penetrate into the calcareous substrates, giving rise to upright fronds, Plants become apparent in April in Galway Bay as small upright fronds, start to reproduce in August/September, and reach their maximum size in December, at which time they start to degenerate. Details of the reproduction of field-collect ed material are given which correspond weU with previously-published descriptions of the reproductive structures of other Halymenia species. Carpospores isolated into laboratory culture. produce plants with a normal morphology when grown on Shells but not when grown on glass slides. Tetrasporangia are formed on the resulting upright fronds in both 16:8h (LD) and 8:16h (SD) photoregimes at 15 °C but the number of tetrasporangia formed at SD is significantly greater than at LD. Nightbreaks (8:73: l :?75h photoregime) at 15 °C are effective in reducing to control LD levels the numbers of tetrasporangia formed. It is concluded therefore that a true, although not absolute, photoperiodic response is involved in tetrasporogenesis in this species. Daylengths of 20 h completely inhibited tetrasporangial initiation. Some tetrasporangia were formed at 10 °C, 8:T6h but not at 10 °C, 16:8h. Tetraspores from laboratory-cultured plants give rise to plants bearing both carpogonial and auxiliary ampullae at 15 °C, 8:16h. Monosporangia are not found in any phase of the life history, which appears to be of the Polysiphonia-type.

Winter fragmentation of Codium fragile (Suringar) Hariot ssp. tomentosoides (van Goor) Silva (Chlorophyceae, Siphonales) in New England

Abstract Winter fragmentation of the upright fronds of Codium fragile ssp. tomentosoides is recorded for the first time. Maximum fragmentation occurs from January to March in New England. Temperature is suggested as the causative factor. The largest fronds of Codium (i.e. those over 8 cm in length) are most susceptible to fragmentation.