Chromosomal distribution of rRNA genes in the karyotypes of two dioicous liverwort species from the genus Pellia Raddi

Over one hundred years have passed since the first cytogenetic studies were made on the liverwort genus Pellia Raddi. The karyotype of Pellia is characterised by large chromosomes, a varying heterochromatin content and the presence of sex chromosomes in the dioicous species. Most of the Pellia species are diploids with n?=?9, but one of them, Pellia borealis Lorb., has been described as an example of allopolyploidy in liverworts. Although the localisation of rRNA genes, which are essential components of the nuclear genome, remains a challenge in bryophytes, data on the number and chromosomal localisation of 35S and 5S rDNA in all of the Pellia species are now available. Previously, fluorescence in situ hybridisation using rDNA probes was performed on the mitotic chromosomes of 2 monoicous species. The aim of this study was to establish the number and chromosomal distribution of rRNA genes in 2 dioicous diploid species—Pellia endiviifolia (Dicks.) Dumort. and Pellia neesiana (Gottsche) Limpr. The relationships between the species within the genus Pellia can now be discussed in the context of the localisation of the rDNA sites and the range in the number of rDNA loci among bryophytes can also be verified.     

A cytological study of Pellia epiphylla (L.) Corda in Britain with reference to the status of Pellia borealis Lorbeer

Abstract

The history of Pellia borealis is outlined and its morphology compared with that of P. epiphylla. The techniques for preparing material for chromosome counts are described. Several gatherings of monoecious Pellia with large epidermal cells (P. borealis) were found to be haploid, n = 9. The size of the epidermal cells is shown to be valueless as a character for distinguishing the two species. It is concluded that only P. epiphylla should be retained as a species.

We wish to record our thanks to Dr S. Arnell for examining British material and for helpful correspondence; to Dr A. J. E. Smith for his valuable advice and criticism, and for the use of cytological facilities; and to all those who have contributed material of possible P. borealis.     

Response of bryophytes to exposure and water availability on some European travertines

Abstract

Seventeen travertine-bryophyte taxa were recorded in 212 quadrats from 17 sites, and the cover of the eight commonest species was analysed in terms of aspect, slope, exposure and water relations. Only Aneura pinguis was significantly affected by aspect, while Eucladium verticillatum and Hymenostylium recurvirostrum preferred steep slopes. The last two species, with Didymodon tophaceus, were also found to prefer sheltered sites, while Bryum pseudotriquetrum, Palustriella commutata var. commutata and Pellia endiviifolia were more common in exposed situations. Didymodon tophaceus, Hymenostylium recurvirostrum and Aneura pinguis were mostly confined to seepages and were kept moist by capillarity, while Palustriella commutata var. falcata and Pellia endiviifolia withstood high flows. Cratoneuron filicinum, Palustriella commutata var. commutata and Pellia endiviifolia had wide ecological amplitudes and were among the most frequently recorded species.     

Evolution and speciation in Pellia,with special reference to the Pellia megaspora-endiviifolia complex (Metzgeriales), II. Cytology

Abstract

A unique karyotype within the genus Pellia, both in terms of chromosome structure and in the distribution of heterochromatin as defined by Giemsa C-banding, supports the taxonomic recognition of P. megaspora. Resembling P. endiviifolia more closely than P. epiphylla or P. neesiana in its heterochromatin content, the species differs significantly in karyotype symmetry and the absence of an m-chromosome. Comparison of P. endiviifolia from Britain, Japan and Canada has identified clear and extensive evidence of cytological polymorphism.     

Studies on Dawsonia superba Grev. II. Growth rate

Abstract

The shoot growth of plants in two clumps of Dawsonia superba was monitored in conjunction with temperature, humidity and throughfall for one year. Growth was found in both cases to be strongly positively correlated with mean air temperature. In one clump a negative correlation with mean atmospheric water deficit was also found. Growth rates as high as 48 mm per year were obtained for the fastest growing plants. Average growth rates were 24 mm per year for Clump I and 15 mm per year for Clump 2.     

Comparative experiments on temperature responses of bryophytes: assimilation,respiration and freezing damage

Abstract

(1) Temperature-net assimilation and temperature-respiration curves based on manometric measurements at high carbon dioxide concentrations are presented for twenty-three mosses and five hepatics.

(2) In most of the species, the optimum temperature for net assimilation under the experimental conditions was about 25°–30°C and the temperature compensation point about 35°–40°C.

(3) Substantially lower optima and maxima were found in Orthothecium rufescens, Plagiopus oederi, Acrocladium trifarium, Fontinalis squamosa, Nardia compressa and Hookeria lucens.

(4) Several northern and montane species (e.g. Anthelia julacea, Andreaea nivalis, Rhacomitrium lanuginosum) did not differ substantially from the majority of lowland species in the response of net assimilation to temperature. Some substantial differences were found between species of differing habitats.

(5) Most of the mosses and leafy liverworts tested withstood rapid cooling to ?5°C for 6 hr. They are evidently protected from intracellular freezing at normal rates of cooling by the withdrawal of water to form extracellular ice.

(6) Conocephalum conicum, Targionia hypophylla and Pellia epiphylla were killed by rapid cooling to ?5°C.

(7) Plagiochila spinulosa and Myurium hebridarumwithstood periods of 1–2 weeks at ?5°C. Survival of bryophytes for long periods of low temperatures appears to be principally a matter of desiccation resistance.     

Growth patterns of Mytilopsis leucophaeata,an invasive biofouling bivalve in Europe

Abstract

For the first time, growth of Mytilopsis leucophaeata, an important European fouling species, was investigated. By means of growth cages, individual shell growth of three cohorts, with, respectively, initial shell lengths of ≤5 mm, 10 mm and 15 mm, was monitored in the harbour of Antwerp, Belgium, during 2003 – 2004. M. leucophaeata followed an oscillatory growth pattern with a single summer growing period per year (May to August). Growth decreased during wintertime, but never ceased completely. M. leucophaeata has an average growth rate of <3 – 6 mm year^?1. Temperature was found to be the main environmental factor affecting growth. The von Bertalanffy growth function was used to model growth of individuals ≤5 mm, resulting in L_∞ = 16.7 mm and K = 0.56. Based on a combination of growth of all three cohorts, the hypothetical growth of an average individual mussel could be modelled over a 5-year period, resulting in a maximum length >19 mm with a growth rate of 0.41. Its longevity (more than 5 years) and the positive effect of higher water temperatures on growth, combined with its high resistance to chlorination, provides M. leucophaeata with a high potential for severe and long-lasting biofouling     

Effect of temperature on vegetative growth among isolates of Metarhizium anisopliae and M. flavoviride

Effects of temperature on vegetative growth on a semi-synthetic medium of 22 isolates of Metarhizium anisopliae and 14 isolates of M. flavoviride were determined. The majority of isolates of both species grew between 11 and 32°C; several isolates grew at 8 and 37 °C. None of the isolates grew at 40 °C. Relative growth rate, calculated from the maximum growth rate for each isolate, was significantly affected by temperature and isolate, with significant isolate * temperature interactions. The maximum absolute growth rates among the isolates ranged from 2.5 mm to 5.9 mm/day. Optimal temperatures were generally between 25 and 32 °C with several isolates exhibiting optimal growth at temperatures as high as 32 °C. Overall, relative growth rates were greater in isolates of M. anisopliae than M. flavoviride at temperatures of 25 °C or lower; conversely mean relative growth rates were greater in M. flavoviride than M. anisopliae at temperatures higher than 25 °C. However, the two most cold tolerant isolates at 8 °C were M. flavoviride and the three most heat tolerant at 35 °C were M. anisopliae. Since temperature growth responses varied considerably between isolates, strain selection according to thermal tolerance may be warranted when choosing a strain for development as a microbial control agent.This revised version was published online in October 2005 with corrections to the Cover Date.     

STUDIES OF SPERMATOGENESIS IN THE HEPATICAE. IV. ON THE BLEPHAROPLAST OF BLASIA

Spermatogenesis in Blasia pusilla L. was reexamined with electron optics to help evaluate conflicting results of the two earlier light microscope studies of this species. The present micrographic resumé of spermatid transformation confirms Sharp's observation of centrosomes in very young spermatids and agrees with Woodburn's general account of spermatozoid maturation. Further, male gamete development in Blasia is shown to be closely comparable to that of Marchantia and Pellia. It is concluded that Sharp's report of blepharoplast development in Blasia by fragmentation and coalescence was based on anomalous plant material.     

Distribution maps

Abstract

There are two groups of Pellia peroxidase isozyme phenotypes, one composed of P. epiphylla, P. neesiana and P. borealis, the other of P. endiviifolia from Europe, P. endiviifolia from Japan and P. megaspora. The phenotypes within the second group differ supporting the suggestion that there are three taxa present.     

The hybrid origin of the polyploid liverwort Pellia borealis

Isozyme markers were used to investigate the origin of the polyploid liverwort, Pellia borealis (gametophytic n=18), which was believed to represent an autopolyploid form of Pellia epiphylla (n=9). Enzyme variation was studied in four taxa: polyploid P. borealis, two recently discovered sibling species of P. epiphylla complex, and the closely related P. neesiana (n=9). Gametophytes of the polyploid showed a complex electrophoretic phenotype for three diagnostic enzymes (DIA1, MPI1 and ACO) in contrast to simple pattern in all haploid taxa. It was postulated that the pattern found in the polyploid represents a fixed heterozygous phenotype resulting from allopolyploidy. Alleles present in the polyploid were found (with only one exception) in the two sibling species of the P. epiphylla complex, suggesting that they are the parents of the allopolyploid. Pellia neesiana was excluded as a donor of either of the genomes. Variation in the polyploid suggests at least three separate origins of P. borealis.     

Himalayan Moss Notes

Abstract

Studies of the relative and absolute lengths of mitotic chromosomes show that Pellia endiviifolia is cytologically distinct from the species P. megaspora, P. epiphylla and P. neesiana. This supports the recognition, on morphological grounds, of P. megaspora as a species distinct from P. endiviifolia.     

Optimization of diet and culture environment for larvae and juvenile freshwater pearl mussels,Hyriopsis (Limnoscapha) myersiana Lea, 1856

Summary

Culture of the freshwater pearl mussel, Hyriopsis (Limnoscapha) myersiana, was carried out in three consecutive steps: (1) culture of glochidia larvae in artificial media, (2) rearing the early juveniles (0–120 days old) in a nursery, and (3) rearing the juveniles (120–360 days old) in an earthen pond. The percentage survival of glochidia in standard tissue culture medium (M199) supplemented with common carp plasma was 95±2.5. All surviving larvae (100%) transformed to juveniles, the duration of transformation being 8 days. The early juveniles (0–60 days old) were fed with a mixture of four selected phytoplankton species (Chlorella sp., Kirchneriella incurvata, Navicula sp. and Coccomyxa sp.). The survival rate of juveniles was 8±0.2%. The average length of these juveniles increased from 0.13±0.01 mm to 1.41±0.16 mm and the average height from 0.16±0.01 mm to 0.98±0.09 mm. Subsequently, 60–120-day juveniles were fed with one of the same four phytoplankton species or a combination of the four. Feeding the juveniles with K. incurvata resulted in the highest survival rate (65±8.32%), with an average length of 3.46±0.04 mm and an average height of 1.94±0.04 mm. Finally, the 120–360-day juveniles were cultured in an earthen pond. There were progressive changes in average weight (0.0037±0.002 g to 11.24±5.02 g), length (3.48±0.39 mm to 54.08±6.21 mm), height (1.97±0.24 mm to 25.09±2.48 mm) and width (0.98±0.06 mm to 12.28±3.21 mm) from 120 to 360 days. The average growth rates per day of these parameters were 0.0497±0.01 g, 0.2414±0.15 mm, 0.0975±0.08 mm and 0.0493±0.03 mm, respectively. H. (L.) myersiana juveniles developed the complete structural composition of the adult by 160 days, and at 360 days, gametogenesis was complete.     

Evolution and speciation in Pellia,with special reference to the Pellia megaspora-endiviifolia complex (Metzgeriales), I. Taxonomy and distribution

Abstract

The genus Pellia, with three currently recognised species, includes a relatively primitive taxon, P. endiviifolia, in which the perichaetium is high and incised, with an enclosed calyptra. It is dioecious, produces anthocyanin wall pigments in exposed sites, reproduces asexually by repeatedly furcate, narrow fragmenting ‘autumnal innovations’, is freely branched and has relatively small spores. A species previously confused with this taxon, and here described as P. megaspora, is an endemic boreal American species, found from New York, Connecticut and Massachusetts north to Newfoundland and west to Minnesota. The plant has a tall perichaetium that is strikingly incised-ciliate to lacerate. It is dioecious but does not produce wall pigments and autumnal innovations, is simple or oncefurcate and has extremely large spores. Cytological and biochemical data support the specific recognition of P. megaspora. Biochemical data also suggest that Japanese populations currently assigned to P. endiviifolia are distinct and field observation suggests that these plants may represent an autonomous subspecies.     

Effects of Temperature and Culture Media on Vegetative Growth of an Entomopathogenic Fungus <Emphasis Type="Italic">Isaria</Emphasis> sp. (Hypocreales: Clavicipitaceae) Naturally Affecting the Whitefly, <Emphasis Type="Italic">Bemisia tabaci</Emphasis> in Texas

The effects of temperature and mycological media on mycelial growth and estimates of spore production of an indigenous entomopathogenic fungus, Isaria sp., found during natural epizootics on whiteflies in the Lower Rio Grande Valley of Texas, were investigated. The radial growth (mm/day) of Isaria sp. as a function of temperature fits a linear model; with faster growth on Sabouraud dextrose agar with yeast extract, SDAY slopes (0.23) than on Sabouraud maltose agar, SMA slopes (0.14) from 20 to 30°C, with an optimal temperature of 30°C (SDAY: 4.1 mm, SMA: 3.1 mm). Moderate growth occurred at 25°C (SDAY: 3.4 mm, SMA: 2.7 mm). Growth was lowest at 20°C (SDAY: 1.9 mm, SMA: 1.8 mm). No fungal growth was observed at 35°C and 40°C. However, when Isaria sp. was exposed to 35°C for the first 7 days, it could recover and grow when transferred to 25°C (SDAY: 3.5 mm, SMA: 2.8 mm). No recovery or growth occurred after transfer from 40°C to 25°C. The average conidial production on SDAY after 20 days incubation at 25°C and a photoperiod of 14:10 h light: dark was 1.2 × 10⁸ conidia/cm² with 100% spore viability. When compared on SDAY at 25°C, the radial growth rate of I. javanica ex type CBS 134.22 (5.1 mm/day) was greater than seven Isaria isolates including Isaria sp.; but maximum growth rates were similar among all related Isaria isolates (90–97%). The Isaria sp. fungus tolerates high temperatures (35°C), suggesting that it is naturally selected for the subtropical semi-arid environment, where it could serve as an important natural control agent of the sweet potato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) biotype B, one of the most invasive and economically damaging insects to agriculture. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U. S. Department of Agriculture.     

热带喀斯特森林多花白头树木质部年内生长动态及其对环境因子的响应

多花白头树(Garuga floribunda var.gamblei)是西双版纳热带喀斯特森林中常见的落叶树种,容易受水分亏缺的影响。为探究热带喀斯特森林树木年内生长动态及其对环境因子的响应,该研究利用生长环和微树芯两种方法监测了多花白头树在2020—2021年的树干径向变化和木质部生长动态,并分析了树干径向变化和木质部生长与环境因子的相关性。微树芯法的监测表明,在2020年,多花白头树在3月底开始出现扩大细胞,9月底细胞壁加厚结束;在2021年,多花白头树在4月中旬开始出现扩大细胞,10月中旬细胞壁加厚结束。生长环的监测表明,2020年和2021年的径向生长开始时间均晚于扩大细胞出现时间,径向生长结束时间均早于细胞壁加厚结束时间。多花白头树在2020年和2021年的木质部生长持续时间大致相同,2020年的木质部生长量((2.87±1.46)mm)也与2021年((2.98±1.02)mm)几乎一致。多花白头树的月径向生长量、扩大细胞区域宽度和细胞壁加厚区域宽度均与降水呈显著正相关,这表明水分状况在多花白头树的木质部生长过程中发挥了重要作用;扩大细胞区域宽度还与日平均气温和日最低温显...     

升温突变对川西道孚林线川西云杉和鳞皮冷杉生长的影响

高山林线作为理想的全球气候变化监测器,是研究植被与气候变化关系的重要场所。利用川西道孚县高山林线川西云杉（Picea likiangensis var.balfouriana）和鳞皮冷杉（Abies squamata）的年轮宽度资料,基于树木年代学的方法,构建差值年表并通过升温突变前后（1995年前后）年轮指数与气候要素的相关分析,探讨了该区林线主要针叶树种的年轮响应变化,为研究青藏高原地区树木与气候响应关系提供研究基础。结果表明：（1）年尺度上,1995年气温突变前后川西云杉和鳞皮冷杉年轮指数和生长弹性时间变化趋势均不显著,没有发生显著的响应分歧现象。（2）月尺度上,升温突变前川西云杉年轮指数与前一年11月月均最高温、5-7月月均温、6月月均最高温、7月月均最低温呈显著正相关;鳞皮冷杉则与前一年11月月均温、11月月均最高温和12月月均温呈显著正相关;表明升温突变前林线树木生长分别受夏季和冬季温度控制;升温突变后川西云杉年轮指数与前一年11月月均温呈显著负相关,和当年2月降水量及7月月均最低温呈显著正相关;而鳞皮冷杉则与当年5月月均温和5月月均最低温呈显著负相关,与5月降水的正相关性达到最大;表明升温突变后林线川西云杉生长依然受夏季温度控制,而鳞皮冷杉生长则受到春季干旱胁迫的影响。未来气候若随着升温出现干暖化,则林线鳞皮冷杉可能会发生明显的响应分歧现象。     

Growth of Leucobryum glaucum cushions In a Berkshire oakwood

Abstract

Radial growth of cushions of Leucobryum glaucum was studied by the crankwire method over two years in an oakwood at Mill Pond, Easthampstead, Berkshire. At this site L. glaucum is the dominant ground flora species on acidic peat and forms some exceptionally large cushions (largest 2 m long, 1.5 m wide, 55 cm high). Growth was unrelated to initial cushion radius and proceeded at a similar rate on all faces of the cushions (overall average, 9.1 mm yr^-1). Estimates of the age of the largest cushion range from sixty to eighty-four years depending on the radius measurement used. Growth rate was highest during the summer and autumn. It was unrelated to variations in precipitation but correlated strongly with air temperature, particularly accumulated temperatures (day-degrees) above 5°C. Evidence is discussed in support of the proposal that L. glaucum is relatively thermophilic. The large cushions at Mill Pond probably result from a combination of favourable circumstances including the warm southern locality, the moist acidic soils, a humid sheltered microclimate and protection from disturbance.     

Embryonic duration and post-embryonic growth rates of the tropical freshwater shrimp Caridina nilotica (Decapoda:Atyidae) under laboratory and experimental field conditions

SUMMARY. Embryonic durations and post embryonic growth rates of Caridina nilotica were determined under laboratory conditions at constant temperatures near 18, 24 and 30°C. Embryonic durations and intermoult intervals were negative curvilinear functions of temperature. At a given temperature moulting frequency varied inversely with shrimp size and slight sexual differences were apparent. Moulting frequency of berried females was governed by the temperature-specific embryonic durations. Growth rates were determined from changes in carapace length (CL) of individual shrimps (laboratory) or batches of shrimps (field enclosures) over 1 month and these data were used to calculate temperature-specific life-long growth curves for males and females. Growth in body mass was estimated indirectly from the carapace length-mass relationship of C. nilotica. On average, males grew marginally faster than females during the first 2 months of life, but growth of males larger than CL= 4 mm was considerably depressed relative to that of females. Inflexions in growth rate, apparently related to the onset of sexual maturity, were apparent in both sexes. Under laboratory conditions, the growth rate of males increased with temperature, but temperature-related differences were not as marked in females. Notwithstanding the more rapid moulting rate at 30°C the growth rate of females was slightly slower at 30 than at 24°C as a result of marginally but significantly smaller per moult growth increments observed at 30°C in animals up to CL= 5.5 mm. Possible reasons for this depressed growth are discussed. Growth rates of animals in field enclosures in Lake Sibaya over 1 month in winter (20 ± 3°C) were generally comparable to those estimated for the 18°C laboratory experiments. Growth rates in enclosures containing tripled standing stocks were almost identical to those containing the naturally occurring biomass of animals, suggesting a non-limited environment at least during the time of the experiment.     

Simulations of the Ontogeny of Spongiophyton, a Devonian Plant

Mathematical representations of the cellular organization anddimensions of Spongiophyton Krusel, a Middle Devonian thallophytewere projected by means of a computer to simulate patterns ofdevelopment and organization. Extrapolation of the cellularpatterns observed on the surface of the fossil may be comparedwith those derived from living plants of which the ontogenycan be directly observed. Spongiophyton is compared in thisrespect with the growth of Protosalvinia (an Upper Devonianplant of enigmatic affinity), Pellia (a thallose liverwort)and Cutleria (a brown alga). The growth pattern of Spongiophytondeveloped by computer shows a closer similarity to that of thepseudoparenchymatous alga Cutleria than to the truly parenchymatousPellia or the fossil Protosalvinia. Computer simulations ofthe growth process throw light on the affinity of Spongiophytonwhich cannot be derived from direct observation of the fossil.Broader applications of computer simulations of tissue organizationand gross morphology are suggested with regard to the studyof living and fossil plants.