Phenological and growth responses of Papaver radicatum along altitudinal gradients in the Canadian High Arctic

Phenology and growth of Papaver radicatum Rottb. was monitored over four summers (1990–1993) at 12 sites, along a dolomitic and a granitic altitudinal gradient (330 m a.s.l.–770 m a.s.l.) at Sverdrup Pass, central Ellesmere Island, Canada. The gradients provided substantial differences in environmental characteristics. Three of the four seasons (1990, 1991 and 1993) had more than 400 thawing degree-days (TDD) in the valley, while the 1992 season had less than 300. The granitic sites had consistently higher temperatures than the dolomitic sites, despite their northerly aspect. Increasing elevation reduced total degree-day accumulation ( c . 40 degree-days/100 m) and length of potential growing season. The proportion of the population producing flower buds was similar at all sites in any given year, but there were differences among years. Production of flowers and fruits per site, decreased with altitude along the dolomitic gradient in 1991 and 1992. There was no difference in the number of buds or flowers produced per plant with increasing altitude, although larger plants with multiple flowers were found only on low elevation granitic sites. Plants from the dolomitic sites were smaller and flowered, on average, after the site accumulated 150 degree-days, while plants on the granitic sites were larger and bloomed after 200 degree-days. Papaver is able to grow and reproduce over a wide range of environmental conditions and moderate climate warming would likely promote its growth and establishment, unless other factors, especially snow-free periods and water availability, become limiting.     

Responses of High Arctic wet sedge tundra to climate warming since 1980

The global climate is changing rapidly and Arctic regions are showing responses to recent warming. Responses of tundra ecosystems to climate change have been examined primarily through short‐term experimental manipulations, with few studies of long‐term ambient change. We investigated changes in above‐ and belowground biomass of wet sedge tundra to the warming climate of the Canadian High Arctic over the past 25 years. Aboveground standing crop was harvested from five sedge meadow sites and belowground biomass was sampled from one of the sites in the early 1980s and in 2005 using the same methods. Aboveground biomass was on average 158% greater in 2005 than in the early 1980s. The belowground biomass was also much greater in 2005: root biomass increased by 67% and rhizome biomass by 139% since the early 1980s. Dominant species from each functional group (graminoids, shrubs and forbs) showed significant increases in aboveground biomass. Responsive species included the dominant sedge species Carex aquatilis stans, C. membranacea, and Eriophorum angustifolium, as well as the dwarf shrub Salix arctica and the forb Polygonum viviparum. However, diversity measures were not different between the sample years. The greater biomass correlated strongly with increased annual and summer temperatures over the same time period, and was significantly greater than the annual variation in biomass measured in 1980–1983. Increased decomposition and mineralization rates, stimulated by warmer soils, were likely a major cause of the elevated productivity, as no differences in the mass of litter were found between sample periods. Our results are corroborated by published short‐term experimental studies, conducted in other wet sedge tundra communities which link warming and fertilization with elevated decomposition, mineralization and tundra productivity. We believe that this is the first study to show responses in High Arctic wet sedge tundra to recent climate change.     

The Development of Radial and Biradial Symmetry: The Evolution of Bilaterality

SYNOPSIS. Understanding the evolutionary origin of novel metazoanbody plans continues to be one of the most sought after answersin biology. Perhaps the most profound change that may have occurredin the Metazoa is the appearance of bilaterally symmetricalforms from a presumably radially symmetrical ancestor. The symmetryproperties of bilaterally symmetrical larval and adult metazoansare generally set up during the cleavage period while most "radially"symmetrical cnidarians do not display a stereotyped cleavageprogram. Ctenophores display biradial symmetry and may representone intermediate form in the transition to bilateral symmetry.The early development of cnidarians and ctenophores is comparedwith respect to the timing and mechanisms of axial determination.The origin of the dorsal-ventral axis, and indeed the relationshipsof the major longitudinal axes, in cnidarians, ctenophores,and bilaterian animals are far from certain. The realizationthat many of the molecular mechanisms of axial determinationare conserved throughout the Bilateria allows one to formulatea set of predictions as to their possible role in the originsof bilaterian ancestors.     

The use of experimental palaeontology in reproducing the effects of diagenetic flattening on graptolites

The detailed effects of diagenetic flattening on the graptolitc rhabdosomc have been investigated experimentally. The initial procedure, to test the effects of flattening on cylinders constructed from a variety of semi-brittle to plastic materials when compressed in a plaster 'matrix', demonstrates that a degree of rigidity is necessary to prevent lateral spread on diagenetic compression, even when lateral confining pressures are present. A second experiment demonstrates conclusively that the effects of flattening on the thecal style of Dicellograptus complanatus proposed by Briggs & Williams (1981; Lethaia 14) can be simulated. A model of an aseptate diplograptid produced a median depression when compressed but no preservational 'median septum', which is considered to be produced in several diplograptid taxa. It is shown that some diplograptids spread laterally along a median line when flattened in scalariform orientation although this has not yet been achieved experimentally owing to the high degree of compression required. □ Graptolithina, diagenesis, flattening,