Patterns and drivers of aquatic invertebrate diversity across an arid biome

Managing and restoring faunal diversity across large areas requires an understanding of the roles of connectivity and dispersal in driving community patterns. We sought to determine the influence of connectivity, water regime, water source, geographical location, and dispersal traits on patterns of aquatic invertebrate diversity across a continent‐wide arid biome. We compiled data on freshwater invertebrate assemblages from sites spanning the breadth of arid Australia. Univariate analyses (analysis of variance and rarefaction) revealed that alpha and gamma diversity across sites decreased as latitude increased. Multivariate analyses (ordination and analysis of similarity) revealed that community composition had considerable fidelity to geographic regions. Hydrological connectivity was strongly associated with riverine community composition although water rarely flowed (often less than annually). Hydrologically isolated sites (springs and rockholes) supported communities that were markedly dissimilar to hydrologically connected sites, and to each other. We investigated the influence of dispersal on diversity patterns by examining distance decay relationships for each of four dispersal trait groups (obligate aquatic and passive, weak, and strong aerial dispersers) on the basis of geodesic (shortest path) distances between pairs of sites and Mantel tests. We did not detect clear differences between dispersal traits and distance decay relationships at the continental scale, even for the two groups with the lowest dispersal ability (obligate aquatics and passive dispersers). Our results suggest that the loss of hydrological connectivity from water developments in arid lands (for example, the impoundment of intermittent rivers) is likely to affect macroinvertebrates. However, the exact flow mechanisms underlying such changes remain to be determined.     

A novel method for characterisation and quantification of plant root exudates

A microcosm unit is described which readily allows manipulation of experimental conditions to enable the subsequent impact on root exudation release to be monitored with time. Festuca ovina and Plantago lanceolata seedlings were grown in this microcosm unit over a 34 day experimental period under conditions of high (3.75 mol m^–3 N) or low (1.25 mol m^–3 N) nitrate-nitrogen treatment. At the end of the experimental period the seedlings in the microcosms were labelled with [¹⁴C]-CO₂ and the fate of the label within the plant and its release by the roots monitored. Total organic carbon (TOC) content of the collected exudate material was measured throughout the experimental period as well as during the ¹⁴C-chase period and comparison of plant C budgets using these two measurements is discussed. Nitrogen treatment as found to have a greater effect on exudate release by F. ovina than by P. lanceolata seedlings as indicated by both the total organic carbon and ¹⁴C results. The use and applications of the microcosm unit are discussed.     

Allozyme frequencies, heterozygosity and genetic distances following S1 recurrent selection in two synthetic maize populations

 Three cycles of S₁ recurrent selection for yield were carried out in two synthetic maize populations, EPS6 from humid Spain and EPS7 from arid Spain. One-hundred S₁ lines were evaluated from each cycle of selection and the ten highest-yielding S₁ lines were recombined to produce the next cycle. Changes in variability and genetic distances in two synthetic maize populations, following three cycles of recurrent selection, recombining ten S₁ lines in each cycle, were determined. Isozyme analysis was performed on 125 seedlings per cycle of selection (four cycles in each of two populations). Regressions of each allozyme frequency on cycles of selection were performed, genetic distances between populations were determined, and simple correlations between genetic distances and heterosis were calculated. The average heterozygosity per locus was also calculated for each population. Regression analysis did not reveal any common trend between EPS6 and EPS7 for changes in allele frequencies presumably due to selection. The number of polymorphic loci, the mean alleles per locus, and the mean heterozygosity did not show any reduction in variability. Finally, selection did not affect genetic distances among cycles of selection. The agronomic evaluation of the selection program, after three cycles of selection, revealed that the genetic variance was not significantly reduced for most traits, and that the heterosis among cycles of selection of both populations had not changed significantly. The conclusions based on isozyme data supported the deductions made from agronomic data. Three cycles of selection neither caused relevant changes on variability nor on genetic distance among cycles of selection of both maize synthetic populations. These data did not indicate any basis for increasing the number of S₁ lines recombined for recurrent selection. Received: 28 April 1997 / Accepted: 23 June 1997     

Structure of the human genomic region homologous to the bovine prochymosin-encoding gene

Two human genomic libraries were probed with bovine prochymosin (bPC) cDNA. Recombinant clones covering a genomic region homologous to the entire coding region and flanking sequences of the bPC gene were isolated. Human sequences homologous to exons of the bPC gene are distributed in a DNA fragment of 10 kb. Alignment of the human sequences and the exons of bPC reveals that the human 'exons' 1-3, 5 and 7-9 have sizes identical to the corresponding bovine exons, but a nucleotide (nt) has been deleted in the human exon 4 and two nt in the human exon 6. The aligned human sequence and the coding part of bPC gene share 82% nt homology, the value ranging, in separate exons, from 76 (exon 1) to 84% (exons 5 and 6). 150 bp of 5'-flanking sequence of the human gene has 75% homology to the corresponding region of bPC gene and contains a TATA-box in a similar position. A 1-nt deletion in the human exon 4 would shift the translational reading frame of a putative human PC mRNA relative to bPC mRNA, and result in an in-phase terminator spanning codons 163 and 164 in bPC mRNA. Another terminator in-phase with the amino-acid sequence encoded by the bPC gene occurs in the human exon 5 and the second frameshift mutation in exon 6. Thus, the nt sequence analysis of the human genomic region has revealed the presence of mutations that have rendered it unable to produce a full-length protein homologous to bPC and, therefore, we refer to this gene as a human prochymosin pseudogene (hPC psi). Blot-hybridization analysis of human genomic DNA indicates that hPC psi is a single gene in the human genome.     

A relationship between nuclear DNA and RNA synthetic activities and the changes produced by n-methyl-n-nitroso urethane: A study using Amoeba proteus as a single cell model

Changes caused by a carcinogen generally vary from one cell to another even among similar types of cells. The following work investigates the degree to which damage (inhibition of division, lethality, or inherited cellular changes) caused by N-methyl-N-nitroso urethane (MNU) alters at different times during the cell cycle, and relates fluctuations in the sensitivity of cells to changes in their DNA and RNA synthetic activities—possibly in the configuration of their DNA—at the time of treatment.Studies on amoebae exposed to MNU for short periods at 50 different times in their cell cycle led to the following conclusions: amoebae are sensitive to MNU at all ages, but the dose needed to produce lethal damage to young and old cells varies by a factor of 3. Cells are most sensitive at the time of division and during the peak of DNA synthesis. Smaller changes are found during the G₂ phase, some of which occur at times of intensive RNA synthesis. Transfer of nuclei between treated and control cells proved that the changing sensitivity of the cells, as shown by both inherited changes and lethal damage, was dependent on changes in their nuclei. Though the cytoplasm could be affected directly by MNU, i.e. in the absence of a nucleus, supralethal doses 2–6 times whole cell dose were required to either kill the cell or to cause a recognizable change in the offspring of viable cells. Experiments with cells having altered nuclear/cytoplasmic ratios showed that the relative insensitivity of older cells was not due to the increased volume of their cytoplasm. However, a possible involvement of cytoplasm in the repair of nuclear damage is suggested by the ability of control cytoplasm to alleviate some nuclear damage, particularly in S phase cells.     

Changes in proportion of thiol to disulphide in acid-soluble nuclear proteins of Echinus during the first cell cycle

1. DNA synthesis in Echinus esculentus eggs kept at 10°C takes place just after fusion, 0.75–1.5h after fertilization, and at telophase at about 2.67–3.33h after fertilization. 2. An increase in the thiol/thiol+disulphide ratio in acid extracts from washed nuclear fractions of the eggs is found at fusion, at early stages of mitosis and at telophase. When DNA is being synthesized, the relative amount of thiol in the extracts increases. 3. There are at least five thiol-containing histones in the acid extract together with a diffusible thiol peptide containing methyl-lysine and 3-methylhistidine and a thiol-containing acidic protein.     

Protein kinase activities in rat liver nuclei: Effects of age and partial hepatectomy

Selective substrates and inhibitors have been used to measure kinases phosphorylating endogenous proteins in rat liver nuclei during growth and regeneration after partial hepatectomy. Peaks in activity were found at 5, 22, and 29 hours after partial hepatectomy. Administration of ₁ and adrenergic blockers suggested that the Be²⁺ sensitive and cyclic AMP-dependent protein kinases were interdependently regulated by Ca²⁺ and cyclic AMP.     

Thymidine metabolism in regenerating rat liver one to two hours after partial hepatectomy

1. When [(3)H]thymidine was injected intravenously into rats in amounts up to 40mg/kg body wt. and the (3)H radioactivity in the livers measured at 30min, saturation kinetics for thymidine uptake were not found. If the animals were examined 3 min after intravenous injection, saturation could be attained in normal rats with 12mg of thymidine/kg and in partially hepatectomized rats with 4mg/kg. At concentrations of thymidine close to saturation, no differences were found in rate or amount of uptake/g of liver between normal and partially hepatectomized rats 1-2h after operation. 2. Perfusion techniques were used to compare thymidine uptakes in the two sets of rats at concentrations up to 40mum-thymidine. Uptakes with tracer amounts of thymidine after 30min were identical in vivo and in the perfusion studies and were twice as great in livers from partially hepatectomized rats with concentrations up to 40mum-thymidine. 3. At 1.5h after operation there was nearly twice as much beta-aminoisobutyrate present per g of liver from partially hepatectomized as compared with normal rats.     

Regulation of the proliferation of primary rat hepatocytes by eicosanoids

DNA synthesis in primary adult rat hepatocyte cultures was promoted by epidermal growth factor (EGF), arachidonic acid, and prostaglandins E2 and F2 alpha (PGE2 and PGF2 alpha). Growth promotion by EGF was blocked by 0.1 mM indomethacin and 1 mM aspirin, without affecting cell viability. If verapamil was present in the medium when EGF was added, the growth response was inhibited. Hepatocytes stimulated by EGF or arachidonic acid released PGE2 and PGF2 alpha into the culture medium. This was diminished if 0.1 mM indomethacin was also in the medium. The importance of autocrine regulation of hepatocyte growth by prostaglandins is discussed.