Chaos in three species food chains

We study the dynamics of a three species food chain using bifurcation theory to demonstrate the existence of chaotic dynamics in the neighborhood of the equilibrium where the top species in the food chain is absent. The goal of our study is to demonstrate the presence of chaos in a class of ecological models, rather than just in a specific model. This work extends earlier numerical studies of a particular system by Hastings and Powell (1991) by showing that chaos occurs in a class of ecological models. The mathematical techniques we use are based on work by Guckenheimer and Holmes (1983) on co-dimension two bifurcations. However, restrictions on the equations we study imposed by ecological assumptions require a new and somewhat different analysis.     

Lectin-induced deciduoma formation in the pseudopregnant rat

Decidual cell induction in the pseudopregnant rat was examined in this study using the lectin concanavalin A (ConA). The histochemical binding of the lectin to the uterine cell surface at the time of deciduomatic induction was also studied. ConA was found to induce significant deciduomata (decidual-like tissue) in the uterine horn when injected intraluminally on day 5 of pseudopregnancy (PSP). ConA-induced deciduomata appeared as a series of discrete nodules in the uterine horn, reminiscent of the anatomical appearance of normal embryo implantation sites. Deciduoma induction by ConA was greatly reduced by pre-absorption of the lectin with its competitive sugar. Lectin histochemistry revealed binding of ConA to the cell surface on day 5 of PSP. Pre-absorption of the lectin with its competitive sugar also significantly reduced surface binding of the lectin, and this finding may be correlated with the greatly reduced ability of the pre-absorbed lectin to induce deciduomata. Possible mechanisms for the induction of deciduomata by lectins are considered.     

Quantitative trait locus analysis of susceptibility to diet-induced atherosclerosis in recombinant inbred mice

Quantitative trait locus (QTL) analysis is a statistical method that can be applied to identify loci making a significant impact on a phenotype. For the phenotype of susceptibility to diet-induced atherosclerosis in the mouse, we have studied four quantitative traits: area of aortic fatty streaks and serum concentrations of high-density lipoprotein-bound cholesterol (HDL-cholesterol), apolipoprotein A-I, and apolipoprotein A-II (apo A-II). QTL analysis revealed a significant locus on chromosome 1 distal impacting serum apo A-II concentration on a high-fat diet and serum HDL-cholesterol concentration on a chow diet. This locus is presumablyApoa-2, the structural gene for apo A-II. QTL analysis of aortic fatty streaks failed to reveal a significant locus.     

QUANTITATIVE GENETICS OF SEQUENTIAL LIFE-HISTORY AND JUVENILE TRAITS IN THE PARTIALLY SELFING PERENNIAL,AQUILEGIA CAERULEA

We determined the genetic basis of several traits related to overall fitness of Aquilegia caerulea, a perennial herb of the Rocky Mountains in western North America. To obtain measures of heritability relevant to the evolutionary potential of wild populations, we performed full and partial diallel crosses and studied progeny performance in the field. Based on a joint analysis of two designs with a total of 18 parents and 102 crosses, we detected significant maternal variance for seed mass and emergence time, but this component was negligible for later-expressed traits. Low heritability and evidence that maternal effects on seed mass are largely environmental suggest that in this population there is little evolutionary potential for change in seed mass under conditions experienced during the study. Seed mass varied depending on particular combinations of parents and cross direction. Such an interaction can have several different biological interpretations, including that particular maternal parents selectively provision embryos sired by particular pollen genotypes. Width of the first true leaf after 4 wk of growth and leaf size of juvenile plants at years one and two were significantly heritable and positively genetically correlated. Juvenile survival exhibited significant dominance variance, as expected from evidence of inbreeding depression in this trait. In contrast, for other traits that exhibit inbreeding depression in this population (seed mass and third-year leaf size), dominance variance was negligible.     

Direct observation of the iron binding sites in a ferritin

X-Ray analysis of the ferritin of Escherichia coli (Ec-FTN) and of Ec-FTN crystals soaked in (NH₄)₂Fe(SO₄)₂ has revealed the presence of three iron-binding sites per subunit. Two of these form a di-iron site in the centre of the subunit as has been proposed for the ‘ferroxidase centres’ of human ferritin H chains. This di-iron site, lying within the 4-alpha-helix bundle, resemble those of ribonucleotide reductase, methane monoxygenase and haemerythrin. The third iron is bound by ligands unique to Ec-FTN on the inner surface of the protein shell. It is speculated that this state may represent the nucleation centre of a novel type of Fe(III) cluster, recently observed in Ec-FTN.     

Isolation and characterization of restriction endonuclease EclHKI from an Enterobacter cloacae strain

An Enterobacter cloacae strain, producing restriction enzyme EclHKI, was isolated from a decaying potato. The enzyme is an isoschizomer of Eam1105I, which recognizes and cleaves GACNNN!NNGTC. EclHKI was produced at high activity (4×10⁴ U/g wet cells) and was purified from contaminants which interfere with restriction digestion by passing the cell lysate through DEAE-Sephacel and heparin columns. Activity was optimal at 37°C in a medium salt buffer.H.-Y. Chan, Y.-C. Chan and P.-C. Shaw are with the Department of Biochemistry, The Chinese University of Hong Kong, Hong Kong: K.-M. Kam is with the Institute of Pathology, Sai Ying Pun Jockey Club Clinic, Hong Kong.     

Mapping of Murine Fibroblast Growth Factor Receptors Refines Regions of Homology between Mouse and Human Chromosomes

The genes for the fibroblast growth factor receptors Fgfr2, Fgfr3, and Fgfr4 have been mapped in the mouse using an interspecific backcross mapping panel. The Fgfr loci map to previously defined regions of homology between human and mouse chromosomes and provide additional information regarding human/mouse comparative mapping.