Interrelationships among fluorometric analyses of spermatozoal function, classical semen quality parameters and the fertility of frozen-thawed bovine spermatozoa

Cryopreserved spermatozoa from 8 bulls were used to examine the interrelationships among flow cytometric spermatozoal quality assessments and classical semen quality parameters and nonreturn rate estimates of fertility. The integrity of the sperm cell membrane and the functional capacity of the mitochondria were quantified by flow cytometry after concurrent staining with carboxydimethylfluorescein diacetate (CDMFDA), propidium iodide (PI), and rhodamine 123 (R123). For each sample a total of 10,000 stained spermatozoa were simultaneously quantified for the intensity of their green and red fluorescence. Three straws from each bull were each examined initially and following incubation at 37 degrees C for 3 hours to assess the rate of senescence. The proportion of spermatozoa retaining membrane integrity and having functional mitochondria, as determined by CDMFDA and R123 staining, were compared with classical semen quality assessments (sperm motility, acrosomal status, cellular and head morphology, presence of vacuoles/craters and cytoplasmic droplets) and with fertility (nonreturn to estrus rates). For individual ejaculates nonreturn rates, the range was from 61.8 to 78.8%, whereas the cumulative rates of several ejaculates for each bull ranged from 71.3 to 83.5%. The proportion of spermatozoa with functional membranes and mitochondria were positively correlated with the percentage of spermatozoa with normal morphology (r=0.82; P=0.01) and motility after 4 hours of incubation (r=0.78; P=0.02), but not with the estimates of fertility. The actual number of spermatozoa per straw staining with CDMFDA and R123 after 4 hours of incubation at 37 degrees C was correlated with the percentage of spermatozoa with normal morphology (r=0.73; P=0.04). Multiple regression equations indicated that combinations of semen quality measurements could be useful in estimating fertilizing potential.     

Plant clonality: Biology and diversity

The current approaches to the study of clonal plants are reviewed. Most studies concentrate at the level of the ramet and clonal fragment exploring the “microscopic” view of clonal plants, dealing with the translocation of resources, clonal integration, plasticity of growth etc. The information gained, by this approach can be used in the understanding of higher levels of organization within the clonal system either with the help of spatially explicit modelling techniques, or by using means and distributions of size within a population instead of studying individual ramets separately. Plant scientists use the term clone with two meanings, viz. (a) a set of physiologically connected, but potentially independent ramets, and (b) a set of genetically identical, but potentially physically separated individuals. The overlap of these terms differs between individual plant species, depending on the extent of physical separation of the ramets and the degree of physiological integration between the ramets; the lower the frequency of ramet separation, the closer are the physiological and genetic concepts of the clone. Three critical areas seem to be neglected in clonal plant research: (a) the interrelationship between hierarchical levels in clonal plants, (b) the particular spatial structure of their environment, and (c) the importance of clonal plants in different ecological communities.     

A comparison of phytoplankton assemblages in the Chesapeake and Delaware estuaries (USA), with emphasis on diatoms

The Delaware Bay is characterized as having greater nutrient and turbidity levels than the Chesapeake Bay. In reference to these differences, a one year study was conducted to identify any similarities and differences in the phytoplankton populations in these estuaries. The results indicated patterns of similarity in the diatom composition, with the total phytoplankton assemblage forming two site groups along a salinity gradient in each bay. These site groups were associated with stations located in the tidal fresh-oligohaline and meso-polyhaline regions of both estuaries. The seasonal concentrations of diatoms and total phytoplankton in both of these regions were higher in the Chesapeake Bay.Subtle differences between the two estuaries include a more diversified and abundant assemblage of neritic phytoplankters (including dinoflagellates) are present in the lower Chesapeake Bay. In contrast, a diatom dominated community is more characteristic of Delaware Bay. It is suggested the entry of neritic species into lower regions of the estuaries was enhanced by the reduced amount of rainfall and flow rates that occurred during the study period. The greater success of neritic species in the Chesapeake Bay is attributed to the lower turbidity of that estuary compared to Delaware Bay.     

Conjugative Plasmid Transfer between Bacteria under Simulated Marine Oligotrophic Conditions

Marine Vibrio S14 strains and an Escherichia coli strain were starved in artificial seawater (NSS) with no added carbon, nitrogen, or phosphorus. The broad-host-range plasmid RP1 was transferred between the starving S14 strains and also from the E. coli donor to the S14 recipient under oligotrophic conditions, in which mixtures of donor and recipient cells were held on Nuclepore filters either floated on NSS or held such that NSS flowed through the filter. Transconjugants were obtained from S14 donors and recipients starved for at least 15 days before being mixed together for conjugation, whereas transconjugants were recovered from the E. coli donor and S14 recipient for up to 3 days of prestarvation, but not after 5 days. Transconjugants were obtained when there were as few as about 10⁵ and 10⁴ cells of starving S14 donors and recipients, respectively, per ml held on the filters. Starved donor and recipient mixtures incubated at 4 or 26°C, as well as those allowed to mate for 2, 5, or 24 h, all yielded numbers of transconjugants which were not significantly (P > 0.05) different.     

Expression of the Acc1 Gene-Encoded Acetyl-Coenzyme A Carboxylase in Developing Maize (Zea mays L.) Kernels

A mutation (Acc1-S2) in the structural gene for maize (Zea mays L.) acetyl-coenzyme A carboxylase (ACCase) that significantly reduces sethoxydim inhibition of leaf ACCase activity was used to investigate the gene-enzyme relationship regulating ACCase activity during oil deposition in developing kernels. Mutant embryo and endosperm ACCase activities were more than 600-fold less sensitive to sethoxydim inhibition than ACCase in wild-type kernel tissues. Moreover, in vitro cultured mutant kernels developed normally in the presence of sethoxydim concentrations that inhibited wild-type kernel development. The results indicate that the Acc1-encoded ACCase accounts for the majority of ACCase activity in developing maize kernels, suggesting that Acc1-encoded ACCase functions not only during membrane biogenesis in leaves but is also the predominant form of ACCase involved in storage lipid biosynthesis in maize embryos.     

Confocal laser scanning light microscopy of the extra-thecal epithelia of undecalcified scleractinian corals

The extra-thecal epithelia of cryofixed undecalcified, freeze-substituted polyps of the scleractinian corals Galaxea fascicularis and Tubastrea faulkneri and axial and basal polyps of Acropora formosa have been examined, in anhydrously prepared thick slices, by confocal laser scanning light microscopy. The avoidance of chemical fixation and decalcification makes it possible to determine whether previously seen structures are real or artefactual products of swelling, shrinkage and distortion. All of the epithelia of all the corals examined are characterised by well defined intercellular spaces. Mucocytes are present in all cell layers in Galaxea and Tubastrea but are not present in any cell layers in the axial polyp of Acropora although they are abundant in the oral ectoderm of the basal polyps in this coral. Zooxanthellae are absent in Tubastrea, the epithelia of the exert septa of Galaxea and the axial polyp of Acropora. The calicoblastic ectoderm is generally composed of thin squamous cells with large intercellular spaces. At rapidly calcifying regions such as the tips of the exert septa of Galaxea, the calicoblastic cells are elongated with extensive arborisation of the basal regions of the cells. They are separated by large intercellular spaces and contain numerous fluorescent granules. The apical regions of these cells appear to be closely applied to the surface of the skeleton. There is no evidence of a space between the apical region of the calicoblastic cells and the skeleton.     

Biology of the African clupeid Limnothrissa miodon with reference to its small size in artificial lakes

Summary Limnothrissa miodon is a clupeid from Lake Tanganyika which has been introduced to Lakes Kivu and Kariba and which invaded Lake Cahora Bassa. These lakes differ considerably from one another but the biology of Limnothrissa is similar in many respects in all of them. Similarities include its feeding and breeding biology, whilst its populations fluctuate, on both an annual and a seasonal basis, in relation to environmental changes. The major differences between the lakes concern the size to which Limnothrissa grows. Their average length in the two natural lakes, Lakes Tanganyika and Kivu, is about twice the average length in the two artificial lakes, Lakes Kariba and Cahora Bassa. This in turn affects their age of maturity and they breed during their first year in the reservoirs but during their second in the natural lakes. Their growth rates and performance are comparable up to about 6 months of age and the difference in their size seems to be due to high mortality in the artificial lakes where few Limnothrissa survive for more than a year. Possible explanations for their small size include the genetic composition of the original introduction and the unpredictability of the environment. Neither of these explanations is supported by evidence at present. Deficiencies in the available food and the effects of intense predation are probably the most likely causes. In both natural lakes, Limnothrissa are predatory or cannibalistic from 100 mm in length and 12 months in age, and fish in their diet may enable them to survive into their second year. The fish in Lakes Kariba and Cahora Bassa, in contrast, are neither predatory nor cannibalistic to any degree. There are no predatory fish species in Lake Kivu but there is a diverse community of pelagic piscivores in Lake Tanganyika which tends to contradict the predation hypothesis. However, the position of Limnothrissa in the reservoirs probably resembles that occupied in Lake Tanganyika by Stolothrissa which is also a small, annual species. The significance of this phenomenon is that Limnothrissa can maintain a high biomass and productivity in the face of intense predation. This trait may be of importance to fisheries management because it means that their yield can be greatly increased.