Characterizing a zooplankton neighbourhood: small-scale patterns of association and abundance

• 1 This study compares small-scale (i.e. neighbourhood) associations among distributions of phytoplankton, zooplankton, and zooplankton grazing rates using a combination of correlations and analyses of spatial patchiness.
• 2 All zooplankton and phytoplankton populations had patchy distributions. On average, individuals experienced members of their same taxon at a density that was 42% greater than the mean sample density.
• 3 The various zooplankton taxa experienced different average neighbourhoods, even within the same stratum of the lake. For example, Daphnia galeata mendotae (Birge) experienced phytoplankton concentrations that were nearly 50% greater than those experienced by Daphnia pulicaria (Forbes) at the same depth.
• 4 The distributions of the various phytoplankton taxa were positively correlated with each other, but the distributions of zooplankton were negatively correlated, or more often, unrelated to each other.
• 5 Phytoplankton abundance was negatively correlated with zooplankton grazing rates.
• 6 We hypothesize that while phytoplankton distributions are driven by common external factors, the factors that determine horizontal distributions of zooplankton are species specific. In addition, zooplankton grazing appears at least partially responsible for the generation of patchiness in the distribution of phytoplankton.

     

Interaction between chemical and tactile cues in mayfly detection of stoneflies

• 1 Sediments and eleven species of rooted submerged aquatic macrophytes were sampled from twenty-five lakes in southern Quebec to examine species patterns in metal content.
• 2 Linear regression models relating the content of metals in the macrophytes to their sediments demonstrated that the isoetoid (Eleocharis acicitlaris, Eriacaulon septangulare, Isoetes sp. and Sagittaria graminae) and the non-isoetoid species had different plant-sediment relationships. Canopy-forming (Myriophyllum spicatum, Potamogeton amplifalius, P. crispus and P. perfoliatus) and understory species (Elodea canadensis, P. robbinsii and Vallisneria americana) had similar linear regression model slopes, but the understory species had significantly higher intercepts, indicating higher plant metal contents for a given sediment metal concentration.
• 3 We grouped species by their biomass density (biomass (kg)/height (m)), a measure of the packing of the plant canopy, and averaged values for each metal, thereby producing one model per group. Comparison of the models by analysis of covariance revealed no significant differences in metal content. However, the canopy-forming species that occurred in monospecific and mixed species stands (M. spicatum and P. amplifolius) had significantly higher metal content for a given sediment metal content when an understory was present.
• 4 These results show that sediment metal content explains the largest proportion of variation in plant metal content across all sites and species. Deviations from what would be predicted by the most general model are not related to large-scale differences in sediment geochemistry, but to the physical structure of the weedbed within geochemically similar sediments.

     

Distribution, production and role of aquatic macrophytes in a southern Michigan marl lake

A typical marl lake of the Upper Great Lakes region has very few quantitatively important aquatic macrophytes. The macrophytes, however, dominate the total primary production of the lake. Submersed vegetation is extremely sparse on the shallow (less than I m) marl bench that characterizes the littoral of these lakes, and is completely dominated by one. little-known species (Scirpus subterminalis Torr.) between 1 and 7 m. A detailed investigation of the spatial and seasonal distribution of macrophytic species and biomass showed that S. subterminalis strongly dominated the lake (79% of total biomass). S. suhterminalis represented an almost pure stand (to 200 g m^?2 mean annual ash-free dry weight) at all times of the year at intermediate depths of macrophytic growth (1–6 m). Two species of Chara (of eight varieties and forms) were present in significant quantities (12% of total biomass; to 100 g m^?2) but were severely limited to shallow depths (0-S-l m) and protected areas. Several annual submersed angiosperms were present (9% of total biomass), but only two species were quantitatively important. Potamogeton illinoensis Morong. and P. praelongus Wulfen formed brief summer peaks (less than 100 g m^?2) at 3 and 4–6 m, respectively. A striking feature of the seasonal biomass distribution of Scirpus subterminalis was the higher, viable biomass (to 150g m^?2) throughout the winter under ice cover. Cyclic fluctuations of the S. subterminalis populations were discerned at different depths, each with different periodicities. The population at 2 m exhibited a fall peak; that at 4 m had a summer maximum. The lowest overall biomass of S. subterminalis occurred in the 2 m population in June. Chara populations at 0–2 m also exhibited a relatively constant biomass throughout the year. The appearance of Nitella at 7 m in July-October and of Chara at 5 m in September-October was interpreted as an interaction between light, thermal, and carbon stratification. Estimates of macrophytic productivity of perennial (‘evergreen’) species populations whose biomass remains relatively constant throughout the year were made employing several different methods of calculation and turnover factors. All methods resulted in productivity estimates in good agreement with the conservative value of 178 g m^?2 year^?1 for the entire lake. In comparison to the other components (phyto-planktonic, epiphytic and epipelic algae) of the primary production of Lawrence Lake, the aquatic macrophytes constituted a major portion (anuual mean 82·77 g C m^?2 year^?1 or 48·3 %) of the total production of the lake. The low diversity but relatively high quantitative importance of macrophytes in marl lakes is attributed to an adverse dissolved inorganic and organic chemical milieu which inhibits phytoplanktonic production and allows only certain adapted macrophytes to develop strongly. The phenomenon of perennial biomass levels throughout the year is believed to be much more common than previously suspected and has iikely resulted from adaptations of submersed macrophytes to ameliorated conditions of water and temperatures relative to the terrestrial situation in winter.     

Transfer of Immunity to Tumour Isografts by the Systemic Administration of Xenogeneic “Immune” RNA

SPECIFIC immunoreactivity can be conferred on lymphoid cells by incubation with RNA-rich extracts prepared from lymphoid tissues exposed to specific antigens in vivo¹ and in vitro^2,3. We have shown transfer of immunity to tumour specific antigens in vivo⁴ and in vitro⁵ by incubation of syngeneic spleen cells in vitro with RNA extracted from the lymphoid tissues of xenogeneic or syngeneic animals immunized with the tumour to be treated. Administration of these spleen cells to normal animals decreased the development and growth of isografts of the same tumour.     

Thermal Inactivation of Plant Growth: Effects on Cotyledon Metabolism

Temperature exposures which normally decrease growth of Pisum sativum seedlings by 50 % were found to be lethal in plants whose cotyledons were removed. Utilization of the two major reserves, starch and protein, decreased at high temperatures. However, the two enzymes responsible for their hydrolysis were thermostable. It appears that the influence of high temperatures on seedling growth is not due to direct effects of temperature on cotyledon metabolism, but rather indirectly through the axis.     

Biochemical Adaptation to the Environment

SYNOPSIS. Biochemical adaptation to environmental parameterssuch as temperature appears to involve two distinct types ofchanges in the organism's chemistry. On the one hand, the quantitiesof certain molecular species present in the cells may change.Alternatively, the actual types of molecules present may vary.Rainbow trout (Salmo gairdneri) acclimated to warm and coldtemperatures exhibit a striking example of this latter typeof adaptation. For all enzymes we have examined in this species,distinct "warm" and "cold" isozymes are present. The isozymesfound in warmacclimated (18°C) trout function well onlyat temperatures above 10–12°C. The isozymes presentin cold-acclimated (4°C) trout function optimally at 2-5°C,temperatures this species normally encounters in winter. Thesedata, plus information on comparable changes in membrane lipids,lead us to propose that adult poikilotherms may undergo a considerabledegree of "biochemical restructuring" on a seasonal basis. Thefactors which control this "restructuring," and the rates atwhich the process occurs at high and low temperatures, are topicsfor future investigation.     

Regulation of Growth in Avena (Oat) Stem Segments by Gibberellic Acid and Abscisic Acid

The purpose of this study was to analyze the nature of the interaction between gibberellic acid (GA₃) and abscisic acid (ABA) in the regulation of growth in excised Avena (oat) stem segments. Growth, compared to sucrose controls, was inhibited by ABA in the range of 10^?4 to 10^?6M. GA₃-promoted growth was also inhibited by ABA in the same concentration range. A Lineweaver-Burk analysis of the interaction between GA₃ and ABA indicated that ABA acts in a non-competitive fashion with GA₃. This same result was obtained previously with GA₃-indoleacetic acid (IAA) and GA₃-kinetin interactions with Avena stem sections. Our results indicate that ABA can inhibit GA₃-promoted growth within physiological concentrations, and that it is probably acting at a different physiological site from that for GA₃.     

Natural distribution, spread, and variation, in the tobacco mosaic virus infecting Nicotiana glauca in Australia

Nicotiana glauca is a naturalised introduced species widely distributed in Australia. A survey of stands in the central zone of its recorded distribution has shown that a type of tobacco mosaic virus which characteristically induces a bright yellow mosaic symptom (TMV-Y) is commonly associated with N. glauca throughout this zone. Surveys of a natural community of N. glauca less than 5 yr old, and in an experimental block, showed that TMV-Y could spread at a rate, and in a pattern, which could not be explained by contact transmission alone, and which indicated that an airborne vector was probably involved in transmission. These results together have led to the conclusion that the common association of TMV-Y with N. glauca is due to spread of the virus by an unknown vector(s). Seed transmission of TMV-Y in N. glauca has not been detected. Molecular hybridisation analysis has shown that all but one of the TMV-Y isolates studied were related to TMV-U², and that the isolate which was unrelated to U², was partially related to TMV-U¹, TMV-U⁵, and tomato mosaic virus. Selected isolates which showed a close relationship to TMV-U², also showed a close relationship to TMV-U⁵, a distant relationship to TMV-U¹, and tomato mosaic, and very little or no relationship with three other tobamoviruses (sunn-hemp mosaic virus, odontoglossum ringspot virus, and cucumber virus 4). These results show that the Australian TMV-Y isolates are similar to the TMV isolated from N. glauca in California.     

A Comparison of Petiolar Growth of Isolated Hazel Cotyledons in Response to Stratification and Exogenous GA3

Following stratification seeds of Corylus avellana exhibitedtheir characteristic ability to germinate at 20 °C undermoist conditions. Stratification of the intact fruit also stimulatedelongation of the cotyledonary petiole when isolated cotyledonswere transferred to moist conditions at 20 °C. GA₃ inducedboth of these effects in non-stratified material. ABA substantiallydecreased seed germination and the response of cotyledonarypetioles to stratification and GA₃. CCC² applied to stratifiedor GA₃-pretreated cotyledons did not depress the final percentageof growing petioles. Cotyledons can clearly regulate the development of their petiolesin the absence of the embryonic axis. It is concluded that thereis at least one gibberellin-sensitive site in the cotyledonscapable of initiating petiole development independent of axiscontrol.     

Aspects of Scotia Sea zooplankton

Information on small scale distributions of three species of Antarctic zooplankton is reviewed. Aggregations of the euphausiid Euphausia superba , the tunicate Salpa thompsoni , and the amphipod Parathemisto gaudichaudii are compared, and the manner in which such aggregations mav arise is discussed. A possible relationship between swarming and feeding activity in E. superba is suggested in which krill are thought to be dispersed whilst feeding but that on repletion they swarm. It is thought that this may account for this species' irregular spatial distribution as recorded bv previous expeditions. A further consequence of this theory is that during the Winter swarming will be minimal.