Structural and dynamic states of actin in the erythrocyte

Analysis of the nucleotide tightly associated with isolated erythrocyte cytoskeletons show it to be ADP, rather then ATP. This confirms that at least a major part of the erythrocyte actin is in the F-form. A re-evaluation of the stoichiometry of spectrin and actin in the erythrocyte (taking account of a gross difference between the color responses of the two proteins on staining of electrophoretic gels) leads to values of 1x10(5) and 5x10(5) for the number of molecules of spectrin tetramer and actin respectively per cell. It has been found possible to perform spectrophotometric DNAase I assays fro actin on lysed whole cells. The concentration of monomeric actin at 0 degrees C is approximately 16 μg/ml packed cells. After washing the lysed cells the monomer pool is not re-established, indicating that only a small proportion of the actin subunits are free to dissociate. The actin monomer concentration in the cytosol remains unchanged after equilibration of the cells with cytochalasin E. The ability of actin-containing complexes in the membrane to nucleate the polymerization of added G-actin was measured fluorimetrically; it was found that membranes incubated with cytochalasin E were completely inert with respect to nucleating activity under conditions that favor appreciable growth at the slowly-growing (“pointed”) ends of free actin filaments. This suggests that these ends of the actin “protofilaments” in the red cell are blocked or sterically obstructed. After treatment of the membranes with guanidine hydrochloride under conditions that dissociate F-actin, the measured concentration of actin monomer rises to approximately 180 μg/ml of packed cells, which is nearly 70 percent of the total actin content. On treatment with trypsin in the presence of DNAase, the spectrin and 4.1 are extensively degraded, but the actin remains undamaged. This treatment, followed by exposure to guanidine hydrochloride, causes a further rise in the concentration of actin responsive to the DNAase assay to 250 μg/ml of cells, compared with 270 μg/ml estimated by densitometry of stained gels. The oligomeric complex, consisting of actin, spectrin, and 4.1, that is extracted from the membrane at low ionic strength, generates no detectable actin monomer after the same treatment. From literature data on the number of cytochalasin binding sites per cell and our value for the total actin content, we obtain a number-average degree of polymerization for actin in the membrane of 12-17. The results lead to a model for the structure of the cytoskeletal network and suggest some consequences of metabolic depletion.     

Genetic Heterogeneity in a Natural Population of Acanthamoeba polyphaga from Soil,an Isoenzyme Analysis1

Acanthamoeba polyphaga, a free-living, bacterial feeder found in freshwater and soil, reproduces asexually and is morphologicaly distinguishable from other acanthamoebae. Isoenzyme analyses were done on 15 random, clonal isolates from soil. Electrophoretic patterns indicated that enzyme bands occurred in clusters consistent with that of a diploid organism. The data indicates that natural populations of A. polyphaga have a greater genetic diversity than laboratory isolates of other amoebae, resembling the heterogeneity observed for natural populations of bacteria.     

The Fungus-culturing Behavior of Ants

A colony of attine ants begins with a recently fecundated femalecarrying hyphae from the parental garden in a pellet in an infrabuccalpocket. All future food of the colony will be derived from thisnucleus. She digs a cavity in the ground, ejects this pelletand manures it with her liquid excrement. As the hyphae proliferate,eggs are laid on them and the colony is launched. She continuallylicks both the hyphae and the brood. Thus, both salivary andanal excretions play a vital role in the beginning of a colonyand this pattern is repeated by the resulting workers. About60–65% of them in Atta are the minima and these are intimatelyinvolved in brood and fungus care. Their excretions are disproportionatelylarge. About 1/3 of the workers in Atta are 4–6 mm mediaand these cut and prepare the substrate. The 7–9 mm maximasizes and the soldiers (over 9 mm) are less directly involvedin culturing the fungus. The effectiveness of fungus culturing is shown by the rapidbuild-up of gardens. The ants maintain their garden despitesurrounding contamination after a fragment with ants is introducedto a plate of sterile nutrient agar.     

Spatial autocorrelation in biology 1. Methodology

Spatial autocorrelation analysis tests whether the observed value of a nominal, ordinal, or interval variable at one locality is independent of values of the variable at neighbouring localities. The computation of autocorrelation coefficients for nominal, ordinal, and for interval data is illustrated, together with appropriate significance tests. The method is extended to include the computation of correlograms for spatial autocorrelation. These show the autocorrelation coefficient as a function of distance between pairs of localities being considered, and summarize the patterns of geographic variation exhibited by the response surface of any given variable.
Autocorrelation analysis is applied to microgeographic variation of allozyme frequencies in the snail Helix aspersa. Differences in variational patterns in two city blocks are interpreted.
The inferences that can be drawn from correlograms are discussed and illustrated with the aid of some artificially generated patterns. Computational formulae, expected values and standard errors are furnished in two appendices.     

Regional and local (road verge) effects on size and fecundity in Banksia menziesii

Abstract Banksia menziesii is a tree at the mesic end (Swan Coastal Plain) of its range and a shrub at the xeric end (Eneabba Plain). Plants at the xeric end produced, on average, as many cones, set 2.3 times as many seeds and stored 8.8 times as many viable seeds in the crown, as those at the mesic end. Plants on road verges had, on average, 2.5 times larger crowns than those at least 50 m further from the road. Road edge plants produced, on average, 2.5 times as many cones, set 3.1 times as many seeds and stored 3.7 times as many viable seeds as non-edge plants. Greater fecundity at the xeric end, including the road verges, could help offset the greater incidence of adult deaths and the reduced likelihood of seedling recruitment after fire at Eneabba.     

A New Development of the Temperature-Gradient Tunnel

The temperature-gradient tunnel provides a range of constanttemperatures simultaneously within one chamber while maintainingother environmental variables at levels which adequately matchmost of the standards which are current in modern plant growthcabinets. The development described in this paper provides (1) an extensionof the temperature range down to 5 C; (2) an enlargement ofthe growing space to increase the work output and allow factorialcombinations of temperature with other environmental variables:(3) an improvement of access to the growing space; (4) an improvementof the humidification system; and (5) the introduction of controlby computer program, allowing, in particular, the provisionof controlled diurnal fluctuations of temperature. A radicallynew system of steam injection provides both heating and humidification,if required, and also satisfies the criteria for improved access. A specimen experiment involving two levels of light intensityand five constant day-temperatures was conducted in the newtunnel. Data are presented for two of the six contrasted specieswhich were grown simultaneously. The response to the uniformlydebilitating effects of severe shade seemed to be dependentupon the species' partitioning ability with respect to the productionof leaf weight and area. This was linked, in turn, to innategrowth potential. The expression of partitioning ability wassubstantially reduced by departures from optimal temperatureregimes. Controlled environment, temperature, computer control, temperature optima, screening, growth analysis, shade response     

The ecology and conservation status of Madagascar's endemic freshwater crayfish (Parastacidae; Astacoides)

1. Freshwater crayfish of the genus Astacoides are endemic to the highlands of eastern Madagascar. Very little is known about their ecology and how this affects their vulnerability to threats. Working in the Fianarantsoa forest corridor, we used a combination of ecological research (>29 000 crayfish caught and released) and interviews (>130 interviews in 38 villages) to investigate the ecology and status of four of the seven described species. 2. Astacoides species studied showed very slow growth, with growth rates of Astacoides granulimanus and Astacoides crosnieri among the slowest known in any species of crayfish. We found individuals of all three species for which we had growth data which we estimate at more than 20‐years old. The size at which females became ovigerous varied among species. Astacoides betsileoensis withheld reproduction until a large size (only 30% of females were gravid at 60‐mm carapace length, compared with 90% for A. granulimanus). This is likely to make A. betsileoensis particularly vulnerable to overexploitation and we found that only 10% of individuals measured in a market (n = 909) would have reproduced before being caught compared with 35% of the more common A. granulimanus (n = 30 561). 3. Habitat loss is a serious threat to the genus; even A. granulimanus, the most widespread species, was only found in rivers or streams flanked by natural vegetation. Astacoides caldwelli, the rarest species in this study, was found only at low altitudes (<800 m) in rivers draining forested catchments. Habitat loss is particularly rapid in low elevation forest. A. crosnieri was restricted to swampy land that is rapidly being converted to rice fields. Introduced Asian snakehead fish (Channa maculata) may pose a hitherto unrecognised threat to some species, particularly A. betsileoensis. 4. Madagascar's freshwater habitats have great significance for global biodiversity yet conservation effort, as in much of the world, has focused on terrestrial ecosystems. Until recently almost nothing was known about the ecology of Astacoides crayfish, a diverse and economically important genus. Here, we show that members of the genus vary markedly in their reproductive biology, growth rates, habitat requirements and the threats they face. We suggest that habitat loss is an urgent threat, especially to A. caldwelli and A. crosnieri, while overharvesting is probably the most immediate threat to the larger A. betsileoensis. We call for more attention to be paid to Madagascar's exceptional, yet understudied, freshwater biodiversity.