Influence of cyanobacterial diet on Asplanchna predation risk in Brachionus calyciflorus

Asplanchna sylvestrii does not discriminate between groups of Brachionus calyciflorus fed either the cyanobacterium Anabaena flos-aquae or a control diet of Euglena gracilis. We based our analysis on the observed probabilities of attack, capture and ingestion during encounters between predator and prey. While A. sylvestrii was very sensitive to brachionid size, we found no significant affects of prey diet on predatory behavior. Thus, cyanobacterial diet did not influence the short-term predation risk of B. calyciflorus exposed to an effective predator. On the other hand, matched cohorts of A. sylvestrii fed B. calyciflorus cultured on the cyanobacterium reproduced more slowly than those fed the same prey cultured on the control food. With prolonged sympatry, therefore, the long-term risk of Asplanchna predation may be reduced for Brachionus by the latter's consumption of cyanobacteria.     

XY sex reversal syndrome in the mare: clinical and behavioral studies,H-Y phenotype

Summary An inherited genetic disorder causes XY embryos of the horse to develop as mares. On the basis of our study of 38 such mares, we have identified four grades or classes of XY sex reversal according to this scheme: class I, nearly normal female, of which some are fertile; class II, female with gonadal dysgenesis, normal mullerian development; calss III, intersex mare with gonadal dysgenesis, abnormal mullerian development, enlarged clitoris; class IV, virilized intersex characterized by high levels of testosterone. In general, class I and calss II mares were typed H-Y antigen-negative whereas class III and class IV mares were typed H-Y antigen-positive.     

Fine structure,mechanism of heart function and haemodynamics in the prosobranch gastropod molluscLittorina littorea (L.)

Summary The heart, main blood vessels, and associated structures ofLittorina littorea were examined by scanning and transmission electron microscopy. The auricle is subdivided into two compartments, one receiving blood from the gill and opening to the nephridial gland vein, the other connecting with the latter anteriorly and the ventricle posteriorly.Video recordings were made of the beating heart in vivo and revealed that the auricle expelled blood not only to the ventricle, but also the nephridial gland vein at systole and provided further evidence of tidal flow of blood in the vein. There is clear indication that the constant volume mechanism of auricular re-filling is not strictly true inLittorina.Blood pressure in the heart and major vessels was measured using a servo-nulling micropressure system. The rate of formation of urine (derived by filtration of blood through the auricular wall) was measured using [⁵¹Cr] EDTA as a blood marker.Basal blood pressure was slightly above ambient (0.7 cm H₂O). Peak systolic pressure in the ventricle (3.8 cm H₂O) was synchronised with a subambient trough in pericardial pressure (–1.0 cm H₂O); these pressure pulses were out of phase with that of the auricle (2.3 cm H₂O) at systole. The observations are consistent in broad terms with a constant volume mechanism, but this does not take into account urine formation or filling of the nephridial gland vein.A filtration pressure of 1.5 cm H₂O has been demonstrated across the auricular wall throughout the cardiac cycle. Colloidal back pressure appears to be negligible. The mean rate of urine formation is 0.26 l g^–1 min^–1.     

Host Status of Five Weed Species and Their Effects on Pratylenchus zeae Infestation of Maize

The host suitability of five of the most common weed species occurring in maize (Zea mays L.) fields in South Africa to Pratylenchus zeae was tested. Based on the number of nematodes per root unit, mealie crotalaria (Crotalaria sphaerocarpa) was a good host; goose grass (Eleusine indica), common pigweed (Amaranthus hybridus), and thorn apple (Datura stramonium) were moderate hosts; and khaki weed (Tagetes minuta) was a poor host. Only the root residues of khaki weed suppressed the P. zeae infestation of subsequently grown maize. When goose grass, khaki weed, and mealie crotalaria were grown in association with maize in soil infested with P. zeae, goose grass and khaki weed severely suppressed maize root development; this resulted in a low number of nematodes per maize root system and a high number of nematodes per maize root unit. Mealie crotalaria did not restrict maize root growth and did not affect nematode densities per maize root system or maize root unit. Special attention should be given to the control of mealie crotalaria, which is a good host for P. zeae, and goose grass, which, in addition to its ability to compete with maize, is also a suitable host for P. zeae.     

Multiple variants in subtelomeric regions of normal karyotypes

We describe a human genomic cosmid clone, 56.1.1, that contains subtelomeric sequences present on multiple human chromosomes. In particular, using fluorescence in situ hybridization, we have identified 16 sites of hybridization on 12 chromosomes. In a sample of 8 unrelated individuals, 10 of these sites showed interindividual variation. Co-hybridization with other polymorphic probes allowed us to demonstrate cytologically heterozygosity at three sites in six individuals. The chromosomal distribution of hybridization sites in a family strongly suggests that these variants are inherited in a Mendelian fashion. These data show that subtelomeric repeats are a rich source of genetic variability. Possible mechanisms of generation of such variants are discussed.     

Genetic Analysis of a Mouse t Complex Locus That Is Homologous to a Kidney Cdna Clone

A mouse kidney cDNA clone, pMK174, identifies restriction fragment length polymorphisms (RFLPs) that map to two unlinked loci. One, designated D17Rp17, has been mapped near quaking, (qk), on chromosome 17 using three sets of recombinant inbred (RI) strains. A study of several t haplotypes resulted in the identification of t-specific alleles of D17Rp17 that map to the proximal half of the t complex. Neither t-specific nor wild-type D17Rp17 alleles are present in chromosomes carrying either the T Orleans (TtOrl) or the T hairpin tail (Thp) deletions. Comparison with other molecular markers indicates that pMK174 identifies a new proximal t complex locus, Rp17. The second locus identified by pMK174, termed D4Rp18, is tentatively assigned to chromosome 4 by mouse-Chinese hamster somatic cell hybrid analysis.     

Inhibitory Effect of Autoclaving Whey-Based Medium on Propionic Acid Production by Propionibacterium shermanii

Propionic acid production by Propionibacterium shermanii was compared in pasteurized and autoclaved whey-based media. Propionic acid production decreased with increasing whey concentration in autoclaved media but not in pasteurized media. Increasing the yeast extract concentration from 5 to 10 g/liter greatly reduced the inhibitory effect of autoclaving.