Thymus-independent Step in the Immune Response to Sheep Erythrocytes

THE nature of the T and B cell interaction in the response to erythrocyte antigens¹ has been an area of intense interest recently. Perhaps because of the influences of molecular biology, there has been a tendency to invoke specific mechanisms such as informational RNA and thymus specific immunoglobulins as mediators of this synergism. But once it was demonstrated that antigen specific receptors of immunoglobulin nature were on the surface of immune competent cells², it was possible to approach the problem more simply; that is from the viewpoint of control of protein synthesis and/or release of proteins from the cell surface. This communication outlines recent evidence concerning the role of non-specific mitogens in the control of antibody precursor (B cells) and antibody secreting cells.     

Number of meals in a day, maximum weight of food consumed in a day and maximum rate of feeding for brown trout, Salmo trutta L.

Brown trout (live weight 9–302 g) were fed to satiation in each of four meals at seven different water temperatures (range 3.8–18.1°C). The period (Ih) from the start of one meal to the start of the following meal was not significantly affected by the weight (Wg) of the trout, but was negatively correlated with water temperature (T°C). A regression equation described the exponential relationship between I and T, and also estimated the number of meals {N) in a day. Values ranged from one meal at about 4°C t o three meals at about 18°C, The greatest increase in appetite occurred at the end of the period I. The maximum weight offood (Drng) eaten in a day was positively correlated with both W and T, a relationship which was well described by a multiple regression equation. The maximum rate of feeding (Fmg h⁻¹) was not significantly affected by W, but increased from 3.8 to 6.8°C, was fairly constant from 6.8 to 19.3°C, and decreased markedly above 19.3°C. Estimates of D and F(with 95% confidence limits) were applicable to a wide variety offood organisms with the exception of mealworms. From comparisons with the results of other workers, it was concluded that the upper limit ofthe daily energy intake determines the optimum temperature for growth.     

The association of tree species,landform, soils and erosion on Narrabeen sandstone west of Putty,New South Wales

An exploratory study was made of the tree species, landform, soils and erosional sequence along altitudinal transects from interfluve to stream channel in a valley incised into Narrabeen Group sandstones and shales to the west of Putty, NSW. Four groups of soils with similar edaphic features were identified. These ranged from duplex soils on the apparently old and stable valley rim, through eroded earths on zones of depletion and sandy regoliths with thick surface horizons on zones of accumulation, to mature duplex soils with thick surface horizons on the colluvial toeslopes. Four communities of tree species were found associated with the four groups of soils. A Eucalyptus punctata –E. piperita open-forest was found on the stable valley rim and a related Eucalyptus punctata –E. piperita – E. oblonga open-forest to low woodland was found on zones of depletion. An Angophora costata open-forest was found associated with the sandy regoliths on zones of accumulation and a Eucalyptus viminalis – E. tereticornis open-forest to tall open-forest occurred on thick soils of the colluvial waning slopes. It was found that the landform fitted a hypothetical nine unit land surface model. The soil types and plant communities were found to reflect the dominant contemporary pedogenetic and geomorphic processes which are also used to define the units of this model. Erosion was evident in the catchment, and the sequence of alluvial soils on the valley floor was found to be consistent with previous suggestions of widespread slope instability during the Quaternary period. Speculation is offered about the effects of management of the valley, especially in terms of land surface instability.     

Ontogenetic changes in the drifting of four species of elmid beetles elucidate the complexity of drift-benthos relationships in a small stream in Northwest England

1. This study aimed to quantify ontogenetic changes in the drifting of Elmis aenea, Oulimnius tuberculatus, Esolus parallelepipedus and Limnius volkmari (Coleoptera: Elmidae), and to relate their drift to benthic density. Monthly samples were taken over 39 months, using three surface nets at each of two contrasting sites in a small stream: one in a deep section with abundant macrophytes, and the other in a shallow stony section. 2. Most larvae and adults were taken in the drift at night with little variation between catches in the three nets at each site. Day catches were very low, often zero. No significant relationships could be established between mean numbers in the drift catches and benthic densities. 3. When night catches were converted to drift densities (number caught per 100 m³ of water sampled), the latter were positively related to monthly losses in the benthos, but not to benthic densities. A linear regression described the relationship, and equations for the different life‐stages within each species were not significantly different from the equation for all life‐stages combined. However, drift losses were only about 0.07% of total losses in the benthos. A severe spate in October 1967 increased the number of larvae and adults in the drift, but not drift densities, except for immature adults of E. aenea, O. tuberculatus and E. parallelepipedus. 4. Key life‐stages with the highest drift density were the earliest life‐stage soon after egg hatching for E. aenea, the start of the larval overwintering period for O. tuberculatus and L. volkmari, and mature adults during the mating season for all three species. Drift density for E. parallelepipedus was too low to identify a key life‐stage. These key life‐stages corresponded with critical periods for survival in the life cycle, as identified in an earlier study in the same stream. Mortality was high during these critical periods, hence the strong relationship between drift density and benthic losses. The latter relationship was very consistent for different life‐stages within each species, and partially supported the rarely‐tested hypothesis that drift represents surplus production in the benthos.     

Predicting the potential long‐term influence of climate change on vendace (Coregonus albula) habitat in Bassenthwaite Lake,U.K.

1. The long‐term suitability of Bassenthwaite Lake as a habitat for vendace (Coregonus albula) was assessed using two models. The first was the phytoplankton model (PROTECH) that provided temperature and phytoplankton biomass outputs that were used to drive a second model of lake oxygen (LOX). 2. Both temperature and oxygen concentrations were used to define the available habitat for the adult vendace, using 18 °C as an upper and 2 mg L^?1 as a lower threshold, respectively. The outputs of both models were compared with 4 years of observed data for the purposes of validation and produced good simulations of water temperature, total chlorophyll a and oxygen concentrations in the epilimnion, hypolimnion and at the lake bottom. 3. Using the outputs of a regional climate model (RCM) simulating 20 years of both present and future climate conditions for this part of the United Kingdom, both models were re‐run. These data suggest the future climate will cause a mean increase of >2 °C in water temperature, little change in overall phytoplankton biomass and a 10% decline in oxygen concentration. 4. Using the thresholds defined above, the habitat volume will decline greatly under the future climate scenarios, with all of the 20 years simulated having periods of zero habitat volume for >7 consecutive days, primarily caused by high temperature. These results suggest that the long‐term viability of the lake as a habitat for this rare fish is extremely low.