Ecosystem function and species loss – a microcosm study

There are too many kinds of organisms to be able to study and manage each, yet the loss of a single species can sometimes unravel an ecosystem. Such `fusewire species'– critical in the same sense that an electrical fuse can cut out a whole circuit – would be a rewarding focus for research and management effort. However, this approach can only be effective if these `fusewires' represent but a small proportion of the number of species in the system.  

Aim

To demonstrate methods for measuring what proportion of the species in a system are critical to ecosystem function.  

Methods

The prevalence of fusewire species was measured in manipulative experiments on an aquatic microcosm.  

Results

No single genus deletion caused changes in key characteristics of the system.  

Main conclusions

Comparison of these results with other published studies shows that the proportion of critical fusewire species varies amongst different ecosystems. The oxidation pond microcosms were shown to contain no single species indispensable to system function. They appear to be ill-suited to a management strategy which focuses on priority eukaryote species. However, a single study provides no evidence that this result is general or even typical of other kinds of ecosystems; it is presented here as an empirical model. Other methods of investigation are available; they are less experimentally rigorous but more practical. These could provide important guidance in planning an approach to management in a particular ecosystem.     

Effects of progesterone and estradiol-17 beta on uterine secretion of prostaglandin F2 alpha in response to oxytocin in ovariectomized ewes

Twenty ovariectomized ewes were used in an experiment designed to examine the interaction of progesterone, estradiol, and oxytocin in the regulation of uterine secretion of prostaglandin F2 alpha (PGF2 alpha). All ewes underwent a steroid pretreatment that mimicked the changes in progesterone and estradiol which occur during the six days immediately prior to estrus. After pretreatment, ewes were randomly assigned to 1 of 4 treatment groups: 1) control (n = 4); 2) estradiol-17 beta (n = 6); 3) progesterone (n = 4); and 4) progesterone and estradiol-17 beta (n = 6). Progesterone was injected twice daily for 15 days. The dose of progesterone varied with day postestrus in a manner designed to simulate endogenous luteal secretion of progesterone. Estradiol-17 beta was administered in s.c. Silastic implants. The implants maintained circulating concentrations of estradiol at 3 pg/ml. On Days 5, 10, and 15 of treatment, ewes were injected with oxytocin (10 IU in 1.0 ml saline, i.v.). Jugular venous blood samples were collected beginning one-half hour prior to and continuing for 2 hours post-oxytocin injection for quantification of 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM). No changes in concentration of PGFM following injection of oxytocin were observed on Day 5 or 10 in any treatment group. Concentrations of PGFM increased following injection of oxytocin on Day 15 only in groups receiving progesterone. Both the area under the PGFM response curve (p = 0.08) and peak response (p = 0.06) were greater in ewes treated with progesterone and estradiol-17 beta than in those receiving progesterone alone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evolution of a Vκ gene family

To examine the evolution of multigene families we have selected as an example an immunoglobulin light chain variable region subgroup (V24) which has been extensively characterized in inbred mice (Mus musculus domesticus). Homologous genes have been isolated and sequenced from Mus pahari, a genetically and geographically isolated species believed to be the oldest living representative of the genus. Southern blot analysis using probes corresponding to individual genes in this subgroup reveals changes in the overall size of the family occurring at the level of individual genes but not at the level of the entire family. Nucleotide sequence analysis indicates an absence of regulatory sequences such as the CAT and TATA boxes 5 to the coding region, but a decanucleotide sequence involved in light chain expression is highly conserved. Within coding regions highly complex patterns of variation are seen which appear to reflect quite different selective pressures on various subregions of the coding sequence. Complementarity determining regions (CDR) are conserved to different extents, with the first CDR region in all family members being among the most conserved segments of the molecule. Conservation is similarly variable among framework segments, indicating complex and variable evolutionary pressures not only at the level of individual genes or their products but also at subregions within homologous molecules.     

Sick Absence Certification. Analysis of one Group Practice in 1967

Certificates of inability or fitness to work were issued on 6,161 occasions in one year in one group practice. Half the episodes of illness lasted for seven days or less, and two thirds of the episodes ended on a Sunday. Clearly in most cases the doctor does no more than countersign the patient''s declaration of his fitness or not to work. Abolition of short-term medical certification would probably have little effect on absenteeism or the sums paid out as sick benefit.     

Nuclear matrix involvement in sperm head structural organization

Summary— In the sperm nuclei the DNA is packaged into a highly condensed form and is not organized into nucleosome and solenoid but is bound and stabilized mainly by the protamines that arrange the DNA in an almost crystalline state. As demonstrated for somatic cells, the sperm DNA has been reported to be organized in loop domains attached to the nuclear matrix structures. However, the possible role of the sperm head matrix in maintaining the loop organization in absence of a typical nucleosomal structures has not been fully elucidated. By using in situ nick translation at confocal and electron microscope level, we analyzed the organization of the DNAprotamine complex and its association with the sperm nuclear matrix. The data obtained indicate that the chromatin organization in sperm nuclei is maintained during the sperm condensation by means of interactions with the nuclear matrix at fixed sites. The fine stucture of sperm nucleus and of sperm nuclear matrix, investigated on sections and replicas of freeze-fractured specimens, suggests that the lamellar array, observed by freeze-fracturing in the sperm nuclei, could depend on the inner matrix which presents a regular organization of globular structures possibly involved in the maintenance of chromatin domains in highly condensed sperm nuclei also.     

Analysis of centromeric activity in Robertsonian translocations: implications for a functional acrocentric hierarchy

Approximately 90% of human Robertsonian translocations occur between nonhomologous acrocentric chromosomes, producing dicentric elements which are stable in meiosis and mitosis, implying that one centromere is functionally inactivated or suppressed. To determine if this suppression is random, centromeric activity in 48 human dicentric Robertsonian translocations was assigned by assessment of the primary constrictions using dual color fluorescence in situ hybridzation (FISH). Preferential activity/constriction of one centromere was observed in all except three different rearrangements. The activity is meiotically stable since intrafamilial consistency of a preferentially active centromere existed in members of six families. These results support evidence for nonrandom centromeric activity in humans and, more importantly, suggest a functional hierarchy in Robertsonian translocations with the chromosome 14 centromere most often active and the chromosome 15 centromere least often active.     

The homologous operons for P1 and P7 plasmid partition are autoregulated from dissimilar operator sites

The plasmid-partition regions of the P1 and P7 plasmid prophages in Escherichia coli are homologues which each encode two partition proteins, ParA and ParB. The equivalent PI and P7 proteins are closely related. In each case, the proteins are encoded by an operon that is autoregulated by the ParA and ParB proteins in concert. This regulation is species-specific, as the P1 proteins are unable to repress the P7 par operon and vice versa. The homologous ParA proteins are primarily responsible for repression and bind to regions that overlap the operon promoter in both cases. The DNA-binding domain of the P7 auto-repressor lies in the amino-terminal end of the P7 ParA protein. This region includes a helix-turn-helix motif that has a clear counterpart in the P1 ParA sequence. However, despite the common regulatory mechanism and the similarity of the proteins involved in repression, the promoter-operator sequences of these two operons are very different in sequence and organization. The operator is located downstream of the promoter in P1 and upstream of it in P7, and the two regions show little, if any, homology. How these differences may have arisen from a common ancestral form is discussed.