Ageing of juvenile coral grouper (Plectropomus maculatus) reveals year-round spawning and recruitment: implications for seasonal closures.

Temporal patterns in spawning and juvenile recruitment can have major effects on population size and the demographic structure of coral reef fishes. For harvested species, these patterns are crucial in determining stock size and optimizing management strategies such as seasonal closures. For the commercially important coral grouper (Plectropomus spp.) on the Great Barrier Reef, histological studies indicate peak spawning around the summer new moons. Here we examine the timing of spawning activity for P. maculatus in the southern Great Barrier Reef by deriving age in days for 761 juvenile fish collected between 2007 and 2022, and back-calculating settlement and spawning dates. Age-length relationships were used to estimate spawning and settlement times for a further 1002 juveniles collected over this period. Unexpectedly, our findings indicate year-round spawning activity generates distinct recruitment cohorts that span several weeks to months. Peak spawning varied between years with no clear association with environmental cues, and little to no alignment with existing seasonal fisheries closures around the new moon. Given the variability and uncertainty in peak spawning times, this fishery may benefit from additional and longer seasonal closures, or alternative fisheries management strategies, to maximize the recruitment contribution from periods of greatest reproductive success.

Critical research needs for managing coral reef marine protected areas: perspectives of academics and managers.

Marine protected areas (MPAs) are a primary policy instrument for managing and protecting coral reefs. Successful MPAs ultimately depend on knowledge-based decision making, where scientific research is integrated into management actions. Fourteen coral reef MPA managers and sixteen academics from eleven research, state and federal government institutions each outlined at least five pertinent research needs for improving the management of MPAs situated in Australian coral reefs. From this list of 173 key questions, we asked members of each group to rank questions in order of urgency, redundancy and importance, which allowed us to explore the extent of perceptional mismatch and overlap among the two groups. Our results suggest the mismatch among MPA managers and academics is small, with no significant difference among the groups in terms of their respective research interests, or the type of questions they pose. However, managers prioritised spatial management and monitoring as research themes, whilst academics identified climate change, resilience, spatial management, fishing and connectivity as the most important topics. Ranking of the posed questions by the two groups was also similar, although managers were less confident about the achievability of the posed research questions and whether questions represented a knowledge gap. We conclude that improved collaboration and knowledge transfer among management and academic groups can be used to achieve similar objectives and enhance the knowledge-based management of MPAs.

Transgenerational marking of marine fish larvae: stable-isotope retention, physiological effects and health issues.

This study examined the toxicological and physiological responses of a commercially important coral-reef grouper, Plectropomus leopardus (Serranidae), to injection of enriched stable-isotope barium chloride (BaCl(2)) solution. Thirty adult P. leopardus were subject to one of two (138)BaCl(2) injection treatment groups (corresponding to dosage rates of 2 and 4 mg (138)Ba kg(-1) body mass), and a control group in which fish were injected with 0.9% sodium chloride (NaCl) solution. Fish from each group were sampled at post-injection intervals of 48 h and 1, 3, 5 and 8 weeks, at which time blood and tissue samples were removed from each fish. Residual concentrations of Ba and (138)Ba:(137)Ba ratios were measured in muscle, gonad, liver and bone tissues of each experimental fish. Elevated Ba concentrations were detected in all treatment fish tissue samples within 48 h post injection. Residual Ba concentrations decreased throughout the remainder of the 8 week experimental period in all tissues except bone. The BaCl(2) injection had no significant effects on measured whole blood variables or on the plasma concentrations of steroid hormones. Enriched Ba stable isotopes can therefore be used at low dosages to mark larvae of commercially important marine fishes, without adverse effects on the health of the fishes or on humans who may consume them.

Alanine metabolism in acute falciparum malaria.

We investigated the integrity of the gluconeogenic pathway in severe malaria using alanine metabolism as a measure. Alanine disposition and liver blood flow, assessed by indocyanine green (ICG) clearance, were measured simultaneously in 10 patients with falciparum malaria (six severe and four moderately severe malaria). After intravenous infusion of alanine (0.3 g/kg), glucose increments (AUC0-55 min) were lower in patients with severe malaria than in those with moderately severe malaria (median = 508 vs. 808 mmol/min/l; P = 0.055). There were no significant differences in the other metabolite increments (alanine, lactate and pyruvate; P >/= 0.27). The two fatal cases had markedly delayed alanine removal (larger AUC0-55 min), prolonged T(1/2) and slower clearance (P /= 0.07) but the increments of lactate and pyruvate were lower in convalescence. Thus, the ratio of the increments of alanine to those of lactate and pyruvate were significantly higher in the convalescent study (P

The plastid DNA of the malaria parasite Plasmodium falciparum is replicated by two mechanisms.

In common with other apicomplexan parasites, Plasmodium falciparum, a causative organism of human malaria, harbours a residual plastid derived from an ancient secondary endosymbiotic acquisition of an alga. The function of the 35 kb plastid genome is unknown, but its evolutionary origin and genetic content make it a likely target for chemotherapy. Pulsed field gel electrophoresis and ionizing radiation have shown that essentially all the plastid DNA comprises covalently closed circular monomers, together with a tiny minority of linear 35 kb molecules. Using two-dimensional gels and electron microscopy, two replication mechanisms have been revealed. One, sensitive to the topoisomerase inhibitor ciprofloxacin, appears to initiate at twin D-loops located in a large inverted repeat carrying duplicated rRNA and tRNA genes, whereas the second, less drug sensitive, probably involves rolling circles that initiate outside the inverted repeat.

The in vivo conformation of the plastid DNA of Toxoplasma gondii: implications for replication.

The Phylum Apicomplexa comprises thousands of obligate intracellular parasites, some of which cause serious disease in man and other animals. Though not photosynthetic, some of them, including the malaria parasites (Plasmodium spp.) and the causative organism of Toxoplasmosis, Toxoplasma gondii, possess a remnant plastid partially determined by a highly derived residual genome encoded in 35 kb DNA. The genetic maps of the plastid genomes of these two organisms are extremely similar in nucleotide sequence, gene function and gene order. However, a study using pulsed field gel electrophoresis and electron microscopy has shown that in contrast to the malarial version, only a minority of the plastid DNA of Toxoplasma occurs as circular 35 kb molecules. The majority consists of a precise oligomeric series of linear tandem arrays of the genome, each oligomer terminating at the same site in the genetic map, i.e. in the centre of a large inverted repeat (IR) which encodes duplicated tRNA and rRNA genes. This overall topology strongly suggests that replication occurs by a rolling circle mechanism initiating at the centre of the IR, which is also the site at which the linear tails of the rolling circles are processed to yield the oligomers. A model is proposed which accounts for the quantitative structure of the molecular population. It is relevant that a somewhat similar structure has been reported for at least three land plant chloroplast genomes.

An alteration in concatameric structure is associated with efficient segregation of plasmids in transfected Plasmodium falciparum parasites.

Transfection of the human malaria parasite Plasmodium falciparum is currently performed with circularised plasmids that are maintained episomally in parasites under drug selection but which are rapidly lost when selection pressure is removed. In this paper, we show that in instances where gene targeting is not favoured, transfected plasmids can change to stably replicating forms (SRFs) that are maintained episomally in the absence of drug selection. SRF DNA is a large concatamer of the parental plasmid comprising at least nine plasmids arranged in a head-to-tail array. We show as well that the original unstable replicating forms (URFs) are also present as head-to-tail concatamers, but only comprise three plasmids. Limited digestion and gamma irradiation experiments revealed that while URF concatamers are primarily circular, as expected, SRF concatamers form a more complex structure that includes extensive single-stranded DNA. No evidence of sequence rearrangement or additional sequence was detected in SRF DNA, including in transient replication experiments designed to select for more efficiently replicating plasmids. Surprisingly, these experiments revealed that the bacterial plasmid alone can replicate in parasites. Together, these results imply that transfected plasmids are required to form head-to-tail concatamers to be maintained in parasites and implicate both rolling-circle and recombination-dependent mechanisms in their replication.

Protein synthesis in the plastid of Plasmodium falciparum.

The plastid organelle of malarial and other apicomplexan parasites contains ribosome-like particles as well as a genome dedicated largely to specifying components of a protein expression system. We have identified plastid ribosomes using hybridization studies and show that in erythrocytic stages of Plasmodium falciparum a subset of polysomes carries plastid-specified rRNAs and mRNA, supporting the idea that protein synthesis is active in the plastid.

Malaria parasites contain two identical copies of an elongation factor 1 alpha gene.

Elongation factor 1alpha (EF-1alpha) is an abundant protein in eukaryotic cells, involved chiefly in translation of mRNA on the ribosomes, and is frequently encoded by more than one gene. Here we show the presence of two identical copies of the EF-1alpha gene in the genome of three malaria parasites, Plasmodium knowlesi, P. berghei and P. falciparum. They are organized in a head-to-head orientation and both genes are expressed in a stage specific manner at a high level, indicating that the small intergenic region contains either two strong promoters or a single bidirectional one. Both genes are expressed at the same time during erythrocytic development of the parasite. This expression pattern and the 100% similarity of the two genes excludes the possibility that the duplicated genes developed in accordance to the different types of ribosomes in Plasmodium. It is more likely that the duplication reflects a gene dosage effect. Comparison of codon usage in the Cdc2-related kinase genes (CRK2) of Plasmodium, which are expressed at a very low level, with the EF-1alpha genes indicates the existence of a codon bias for highly expressed genes, as has been shown in other organisms.

Anti-TNF treatment does not reverse the abnormalities in lipid metabolism of the obese Zucker rat.

Because obesity, insulin resistance, and hyperlipidemia are often associated, and recent evidence suggests that the cytokine tumor necrosis factor-alpha (TNF) may influence the activity of insulin in various target tissues, the present study was designed to see whether TNF was also associated with the changes in lipid metabolism that lead to hyperlipidemia in the obese model of the Zucker rat. A polyclonal goat anti-rat TNF antibody was subcutaneously administered to Zucker rats for 4 days to block TNF actions. The results indicate that none of the alterations in lipid metabolism seen in the obese animals were reversed by the anti-TNF treatment. This was the case for the lipogenic rate in liver and adipose tissue, the disposal of an exogenous [14C]triolein load, adipose tissue lipoprotein lipase activity, and the hypertriglyceridemia. Measurements of lipolysis in adipose tissue slices from the anti-TNF-treated animals also did not show any significant effect of the treatment. In conclusion, TNF does not seem to be involved in the abnormalities of lipid metabolism observed in the obese Zucker rat.

Extrachromosomal DNA in the Apicomplexa.

Malaria and related apicomplexan parasites have two highly conserved organellar genomes: one is of plastid (pl) origin, and the other is mitochondrial (mt). The organization of both organellar DNA molecules from the human malaria parasite Plasmodium falciparum has been determined, and they have been shown to be tightly packed with genes. The 35-kb circular DNA is the smallest known vestigial plastid genome and is presumed to be functional. All but two of its recognized genes are involved with genetic expression: one of the two encodes a member of the clp family of molecular chaperones, and the other encodes a conserved protein of unknown function found both in algal plastids and in eubacterial genomes. The possible evolutionary source and intracellular location of the plDNA are discussed. The 6-kb tandemly repeated mt genome is the smallest known and codes for only three proteins (cytochrome b and two subunits of cytochrome oxidase) as well as two bizarrely fragmented rRNAs. The organization of the mt genome differs somewhat among genera. The mtDNA sequence provides information not otherwise available about the structure of apicomplexan cytochrome b as well as the unusually fragmented rRNAs. The malarial mtDNA has a phage-like replication mechanism and undergoes extensive recombination like the mtDNA of some other lower eukaryotes.

Organelle DNAs: The bit players in malaria parasite DNA replication.

The replication mechanics of the extrachromosomal DNAs of the malaria parasite are beginning to be anravelled. At 6 kb, the mitochondrial genome is the smallest known and, unlike higher eukaryotes, its multiple copies per cell occur as polydisperse linear concatemers. Here, Don Williamson, Peter Preiser and Iain Wilson discuss recent evidence that this DNA replicates by a process akin to those of certain bacteriophages, which make use of extensive recombination coupled with rolling circles. The parasite's second extrachromosomal DNA, a 35 kb circular molecule thought to be a plastid remnant inherited from a remote photoautotroph, probably replicates in a more familiar fashion from conventional origins or D loops. Improved understanding of both organelle's replicative mechanisms could give new leads to malaria chemotherapy.

Complete gene map of the plastid-like DNA of the malaria parasite Plasmodium falciparum.

Malaria parasites, and other parasitic protists of the Phylum Apicomplexa, carry a plastid-like genome with greatly reduced sequence complexity. This 35 kb DNA circle resembles the plastid DNA of non-photosynthetic plants, encoding almost exclusively components involved in gene expression. The complete gene map described here includes genes for duplicated large and small subunit rRNAs, 25 species of tRNA, three subunits of a eubacterial RNA polymerase, 17 ribosomal proteins, and a translation elongation factor. In addition, it codes for an unusual member of the Clp family of chaperones, as well as an open reading frame of unknown function found in red algal plastids. Transcription is polycistronic. This plastid-like DNA molecule is conserved in several genera of apicomplexans and is conjectured to have been acquired by an early progenitor of the Phylum by secondary endosymbiosis. The function of the organelle (plastid) carrying this DNA remains obscure, but appears to be specified by genes transferred to the nucleus.

Recombination associated with replication of malarial mitochondrial DNA.

Mitochondrial DNA of the malarial parasite Plasmodium falciparum comprises approximately 20 copies per cell of a 6 kb genome, arranged mainly as polydisperse linear concatemers. In synchronous blood cultures, initiation of mtDNA replication coincides with the start of the 4-5 doublings in nuclear DNA that mark the reproductive phase of the erythrocytic cycle. We show that mtDNA replication coincides with a recombination process reminiscent of the replication mechanism used by certain bacteriophages and plasmids. The few circular forms of mtDNA which are also present do not replicate by a theta mechanism, but are themselves the product of recombination, and we propose they undergo rolling circle activity to generate the linear concatemers.

tRNA genes transcribed from the plastid-like DNA of Plasmodium falciparum.

Besides their mitochondrial genome, malarial parasites contain a second organellar DNA. This 35 kb circular molecule has a number of features reminiscent of plastid DNAs. Sequence analysis shows that along with other genes the circle codes for 25 different tRNAs all of which are transcribed. Six of the tRNAs have some unusual features, and one has an intron, the only one found so far on the circle. Comparison of codon and anticodon usage indicates that the 25 tRNAs are sufficient to decode all the protein genes present on the circle. The maintenance of such a parsimonious but complete translation system is further evidence for the functionality of the circle.

Regulation of milk lipid secretion: effects of oxytocin, prolactin and ionomycin on triacylglycerol release from rat mammary gland slices.

A system for the study of the regulation of the release of triacylglycerols by mammary gland slices was developed. By prelabelling the triacylglycerol pool with [3H]oleate measurements of release of both mass of triacylglycerol and of newly synthesized triacylglycerol have been made. Oxytocin and ovine prolactin stimulated release of triacylglycerol and protein, but the former was 40-fold more effective. Recombinant bovine prolactin was even less active than ovine prolactin, suggesting that contamination of the latter with oxytocin and/or vasopressin was partly responsible for its stimulatory effect on release. The findings support the view that the major effect of oxytocin is to stimulate contraction of myoepithelial cells and thus release secreted lipid stored in the lumen of the mammary gland alveoli. Ionomycin, a Ca2+ ionophore, also stimulated lipid release, but probably not by the usual apocrine route. Parathyroid hormone-related protein, a peptide produced by the mammary gland, did not stimulate release or antagonize the effects of oxytocin. Release of lipid was also measured in mammary gland slices from late-pregnant, early- and mid-lactating rats and lactating rats made prolactin-deficient. Hormonal stimulation in vitro showed the maturation of response seen in vivo on transition from late pregnancy to peak lactation. Prolactin deficiency resulted in decreased release of newly synthesized lipid in response to oxytocin.

Acute effects of endotoxin (lipopolysaccharide) on tissue lipid metabolism in the lactating rat. The role of delivery of intestinal glucose.

The aim of this study was to compare the effects of endotoxin on lipid metabolism and, in particular, lipogenesis in virgin and lactating rats. Intraperitoneal administration of bacterial endotoxin (lipopolysaccharide, LPS; 3 mg/kg body wt.) to fed virgin rats caused a 4-fold increase in lipogenic rate in liver in vivo. The stimulatory effect was not seen when glucose (6 mmol) was administered either orally or intraperitoneally to increase the basal rate. In contrast, the rate of lipogenesis in interscapular brown adipose tissue was inhibited, after LPS, and this was relieved by intraperitoneal glucose. In the lactating rat there were no significant changes in hepatic lipogenesis after the administration of endotoxin. However, LPS decreased the lipogenic rate in mammary gland of lactating rats and intraperitoneal glucose administration, but not oral, was able to restore the rate. In both virgin and lactating rats, LPS decreased glucose removal from the intestinal tract. In lactating rats, LPS induced a rise in blood concentrations of lactate, and plasma triacylglycerols and non-esterified fatty acids, similar to those in endotoxin-treated virgin rats. The administration of LPS did not decrease the accumulation of radioactivity in lipid in either liver or in mammary gland after injection of 3H-oleate. In contrast, LPS decreased the accumulation of radioactivity in mammary gland after injection of 3H-chylomicrons and increased it in liver and plasma. These changes were accompanied by a decrease in mammary gland activity of lipoprotein lipase. Intraperitoneal glucose partially reversed these changes in chylomicron disposition.(ABSTRACT TRUNCATED AT 250 WORDS)

High plasma insulin-like growth factor-II and low lipid content in transgenic mice: measurements of lipid metabolism.

Transgenic mice were made by introducing extra copies of the mouse insulin-like growth factor-II (IGF-II) gene driven by the bovine keratin 10 promoter (BKVI). The adult plasma IGF-II levels were elevated at least three times in one line. In this line, there was a lower lipid content of both brown and white adipose depots at 2-4 months of age, and 40% less fat in the carcass at 7-9 months. The low lipid phenotype was not detected in the carcass at 2 weeks after birth. The lean characteristic was attributed to circulating IGF-II because the transgene was not expressed in fat. At 2-4 months of age, the transgenes oxidized more oral lipid, and less of this lipid was incorporated into the whole body and the epididymal fat. In contrast, the interscapular brown adipose tissue maintained lipid incorporation and lipoprotein lipase activity despite its reduced size. The altered activity of the brown adipose tissue may account for the gradual onset and persistence of the lean feature of the transgenic mice. There were no substantial changes in lipogenesis which could account for the low fat content. The plasma levels of IGF-I, insulin, glycerol, non-esterified fatty acids, triacylglycerols and glucose were not greatly changed and the pituitary GH content was within the normal range.