Re-Definition of the Genus Acanthamoeba with Descriptions of Three Species

SYNOPSIS. Ten strains of Acanthamoeba from freshwater habitats were isolated in clonal cultures. Studies were made of trophic structure, nuclear division, cyst structure, some aspects of cytochemistry, and other characteristics. One strain was identified as A. castellanii (Douglas, 1930), one as A. astronyxis (Ray and Hayes, 1954), and 8 as A. polyphaga (Puschkarew, 1913). Strains of Acanthamoeba isolated by other workers were also examined comparatively.
The pattern of nuclear division in all strains resembled that in metazoan cells, with the exception that centrioles were never found. Trophic amoebae had a PAS-positive surface outline. Cyst walls were strongly PAS-positive and also gave a positive test for cellulose with zinc chloroiodide.
The genus Acanthamoeba Volkonsky, 1931 is re-defined, being distinguished from Hartmannella Alexeieff, 1912, emend. Volkonsky, chiefly by the formation of tapering, hyaline pseudopods (acanthopodia) and by a cyst made up of an ectocyst and a polyhedral or stellate endocyst, with excystment by removal of opercula. Other characteristics found in all strains include a distinctive food cup, the presence of many small refractile globules in the cytoplasm of trophic amoebae, and a cyst wall containing cellulose. The degree of spindle convergence, employed by Volkonsky as a generic criterion, was unusable.
Differential diagnoses based principally on cyst structure are offered for A. castellanii, A. astronyxis , and A. polyphaga. The strain previously called Mayorella palestinensis Reich, 1933 is a distinct species of Acanthamoeba.     

Increases in lake phytoplankton biomass caused by future climate‐driven changes to seasonal river flow

For the many lakes world‐wide with short residence times, changes to the rate of water throughput may have important effects on lake ecology. We studied relationships between current and predicted residence times and phytoplankton biomass using a eutrophic lake in the north‐west of England with an annual residence time averaging about 20 days, as a test case. Using 32 years of recent hydrological flow data for Bassenthwaite Lake, multiple sets of scaled flow for each year, and the process‐based phytoplankton response model, PROTECH, we modelled the effects of changing river flow on phytoplankton biomass in the lake. The impact on biomass was shown to depend on seasonal changes in flow rather than annual changes. Furthermore, there was a qualitative difference in impact depending on whether the nutrient loading to the lake came principally from flow‐independent sources, or from flow‐dependent ones. Predictions for changes in river flow under future climate scenarios in the north‐west of England have suggested that, despite little change in the annual flow magnitude, there will be a shift to greater flow in the winter and lesser flow in the summer. Applying these flow predictions to our modelling of Bassenthwaite Lake revealed that, with flow‐independent nutrient loading, and no overall increase in nutrient load, phytoplankton abundance in the summer could increase by up to 70%, including an increased proportion of Cyanobacteria. Conversely, were the loading completely dependent on the flow, the biomass would fall. In many parts of the world, river flow is expected to decrease in the summer even more than in England, suggesting these areas may expect substantial changes to seasonal phytoplankton biomass as a result of climate‐driven changes to seasonal river flow. Such changes would be in addition to any other changes owing to warming effects or eutrophication.     

Cultivation and Lyophilization of Mastigina sp.

SYNOPSIS Mastigina sp. is an amoeboid flagellate isolated from pine frass collected in the Guadarrama Mountains in Spain. It feeds on bacteria and yeasts. It prefers yeasts that produce extracellular polysaccharides, and the 2 species that have been used predominantly for cultivation of the flagellate are Pachysolen tannophilus and Hansenula holstii. Mastigina sp. is easily isolated in axenic culture and grows abundantly therein. Its locomotive form, averaging 27 μ in length, resembles that of a limax amoeba, with a vesiculate nucleus at the anterior end. Cells are capable of simultaneous movement by pseudopodia and flagella. It develops rapidly on dead or living yeast cells in shaken cultures and the trophozoites may convert quantitatively to cysts. The cysts remain viable for long periods of time in refrigerated suspensions and in the lyophilized state. They are spherical or ovoid and smooth-walled cysts; the trophozoite emerges from them by breaking the wall.     

Oviposition behaviour of the grasshopper Zonocerus variegatus

Abstract. 1. Long-term changes in the numbers of Zonocerus at oviposition sites reflect changes in the maturity of the general population.
2. Short-term changes in the numbers of Zonocerus at oviposition sites are associated partly with normal diurnal behaviour in which roosting occurs at night.
3. Immigration of Zonucems , particularly females, into the oviposition site occurs prior to periods of oviposition activity. Emigration follows oviposition.
4. The majority of Zonocerus move upwind into the oviposition site suggesting an odour and/or sound attraction.
5. Periods of intense oviposition activity follow heavy rainfall.     

Toward a Unified Paradigm of Race

Racism in Mind. Michael Levine and Tamas Pataki, eds. Ithaca, NY: Cornell University Press, 2004. 320 pp.
Only Skin Deep: Changing Visions of the American Self. Coco Fusco and Brian Wallis, eds. New York: Harry N. Abrams, 2003. 416 pp.     

Fourteen months of seed rain in three Australian semi‐arid communities

The abundance and composition of seed rain was measured over 14 months (February 2004 to March 2005) in Currawinya National Park, western Queensland. The experimental design included four measurement periods, three vegetation communities and two grazing regimes. A total of 12 586 seeds from 104 species were captured. There were significantly more seeds and species captured during the measurement period with the least rainfall, although no significant correlation was found between the amount of rainfall and the number of seeds or species captured. More seeds and species were captured where native and feral grazing pressure was removed, but this was only significant for the number of species. The above‐ground vegetation showed no significant difference between grazing treatments over the study period and exhibited far fewer species than the seed rain. However, the majority of species found in the above‐ground vegetation were represented in the seed rain. Hypotheses are explored as an attempt to understand the apparent lack of a relationship between seed rain and rainfall. The effects of grazing and seed movement and storage are also discussed.     

Three new species of deep‐sea Gromia (Protista,Rhizaria) from the bathyal and abyssal Weddell Sea,Antarctica

We describe three new species of the genus Gromia from bathyal and abyssal depths in the Weddell Sea. The new species are characterized by a combination of morphological and molecular criteria. All three species possess a distinct oral capsule and a layer of ‘honeycomb membranes’, which form the inner part of the organic test wall. Both these features are typical of gromiids. Their identification as gromiids is confirmed by analyses of partial small subunit ribosomal DNA (SSU rDNA) gene sequences. Gromia marmorea sp. nov. is a rounded species with a prominent oral capsule and a characteristically mottled appearance. In Gromia melinus sp. nov. , the test surface exhibits a polygonal pattern of ridges, with a layer of clay particles coating the surface between the ridges. Gromia winnetoui sp. nov. represents an elongate morphotype in which the organic test is enclosed within an agglutinated case, a feature previously unknown in gromiids. Phylogenetic analysis using the maximum‐likelihood method revealed that all three species form distinct clades, reflecting the morphological differences among Weddell Sea species, as well as between deep‐water Southern Ocean Gromia and previously described gromiids. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 157 , 451–469.