摘要:

Summary1. The concept of evolutionary equilibrium has been derived from the theory of island biogeography via an ecological rationale for increase in species extinction rate and decrease in speciation rate with increasing diversity of the system.2. This concept is theoretically plausible at the species level and at a regional scale but, in spite of several empirical tests in the fossil record, it has thus far remained unsupported by empirical evidence. In order to test it conclusively, one has to analyze not only the pattern of species number through time but also its relationship to speciation and species extinction rates; independent evidence for perturbations must also be available.3. The concept of evolutionary equilibrium at the global scale must be extrapolated over higher levels of taxonomic hierarchy, for reliable species‐level data are unavailable at this scale. A theoretical justification for this concept cannot, then, be derived from the theory of island biogeography.4. The rates of family extinction and origination in the Phanerozoic show no evidence for diversity‐dependence, which undermines most quantitative models of biotic diversification based on the concept of global evolutionary equilibrium. Rigorous testing of these models cannot be done at the present state of knowledge because of the uncertainty about the empirical pattern (sampling and taxonomic biases, absolute time sca

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1985.tb00619.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Summary1. In Limulidae, all the factors involved in the coagulation processes are located inside the amoebocytes. The cellular coagulogen is a single 20,000‐polypeptide‐chain protein. It is converted into a non‐covalently crosslinked gel by a serine protease enzyme which cleaves a single peptide bond, releasing peptice C.2. Pro‐clotting enzyme can be activated by two independent pathways: coagulation is induced by either LPS or 1,3‐β‐D‐glucan, both of which result in gel formation. The two pathways comprise a complex enzyme cascade with several limited protein proteolyses.3. In Decapoda, clotting factors are found in both the cell‐free plasma and haemocyte compartments. Analogous factors are present in Insecta.4. Plasma coagulogen is a 400,000 molecular weight protein with both lipid and carbohydrate moieties. Its soluble polymers are converted into covalently crosslinked polymers of coagulin by Ca2+‐dependent transglutaminase. In crayfish, it is also found in other tissues such as soft integument and calcified cuticle. Its concentration varies greatly with the species investigated. It seems to possess many diversified functions such as plasma coagulation, protein transport of tanning agents, lipid and sugar transport and protein storage, and resembles fibronectin.5. A type of cellular coagulogen seems to be present in the haemocytes of Decapoda. It can be converted to a gel by a serine protease pro‐clotting enzyme. This pro‐enzyme can be activated by either LPS or 1,3‐β‐D‐glucans. The mechanism of LPS action is not entirely clear. 1,3‐β‐D‐glucans also activate the prophenoloxidase system and cause phenoloxidase attachment to foreign surfaces of haemocyte lysates. The latter system is restricted to semi‐granular and granular haemocytes, and plays an important part in host‐defence reactions.6. The evolutin of clotting processes throu

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1985.tb00620.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Summary1. While much attention has been paid to the ecology of macro‐invertebrates in flowing water, the microbial ecology of such systems has been largely ignored and our knowledge of heterotrophic slimes in particular remains far from complete. Slime‐forming organisms are ubiquitous in their distribution and are part of the normal riverine flora. Slime outbreaks occur in all types of organically enriched flowing fresh waters, regardless of their chemical nature. Slimes are predominantly of heterotrophs which require a constant supply of (i) a suitable carbon source, (ii) inorganic nutrients and in particular nitrogen and phosphorous, and possibly (iii) growth factors such as vitamins. Phosphorous is not a limiting factor for growth, with slimes developing in rivers with<0·02 mg P l‐1. Other inorganic nutrients such as nitrogen can be used in various forms and are usually present in adequate amounts, even in unpolluted streams. Therefore occurrence appears to be most closely correlated with the presence of a source of available carbon.2. The severity of outbreaks are not closely associated with soluble organic carbon content although there is a tendency for heavy growths to occur more frequently in more severely polluted waters. Low‐molecular‐weight sugars are clearly the causative agents ofSphaerotilus natansdominated slimes with higher molecular weight material such as starches not immediately effective as growth promoters. Mono‐ to penta‐saccharides are mainly used by bacterial slimes while fungal components utilize fatty acids up to C8. It is not possible to adopt a nationwide BOD5standards to control slime outbreaks as even small increases in river BOD5(<1·0 mg l‐1) can support slime growth. There is a need to develop new methods of assessing the slime‐promoting capability of effluents such as measuring the readily degradable low‐molecular‐weight carbon compounds, so that threshold concentrations of soluble organic carbon below which slime will not develop can be determined.3. The effect of effluent enrichment on slime growth diminishes downstream as there is a tendency for the soluble carbohydrate to mix and dilute. The slime also metabolizes the carbohydrate, reducing the concentration by up to 60 % depending on the stage of slime development, thus limiting its own proliferation. This is the typical pattern of self‐purification in flowing waters.4. The taxonomy of all the slime‐forming species are poorly understood as is the ecology of slimes. Species composition of slimes vary temporally and spatially within individual rivers. The primary factors affecting composition are nutrient type and water velocity, although pH determines whether a slime is either predominantly fungal or bacterial. The rate of transfer of oxygen and nutrients is dependent on water velocity with zoogloeal forms predominating as velocity falls to5 km) resulting in oxygen depletion, increased siltation, alteration in flow pattern, increase in sloughed biomass, reduction in species diversity, destruction and reduction in habitat diversity and the elimination of fisheries. Case studies on the effects of slime growth, especially those causing fish kills, need to be carefully analysed and published.10. The potential of heterotrophic slimes in biotechnology and wastewater treatment has yet to be fully realized. The ability to grow rapidly, producing considerable biomass rich in protein could be utilized. The sorption of heavy metals by all the slime‐forming organisms but especially by the iron and manganese bacteria, could be used for the removal of low concentrations of metals in wastes, treatment of metal‐rich effluents or for metal recovery. The property of removing phosphorous and nitrogen from solution should also be further considered.11. No adequate control measures are available except for full treatment of effluents prior to discharge. Even traces of low‐molecular‐weight carbon compounds will result in slime development. Inadequate partial treatment may enhance slime growth by partially breaking down the effluent and releasing slime‐promoting compounds. Intermittent discharge can reduce the standing crop of slime per unit surface area but as the total biomass supported by an effluent will remain the same, the slime will be extended over a greater length of river. Bacterial slimes are assemblages of filamentous and dispersed bacteria, and are far more common than fungal or algal dominated slimes. The two slime‐forming organismsS. natansand zoogloeal bacteria are the major components of the majority of heterotrophic slimes, therefore any a

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1985.tb00621.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1985.tb00622.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY