The impact of prenatal diagnosis on the occurrence of chromosome abnormalities

From the public health point of view, several formal attempts have been made to measure the impact of prenatal diagnosis (PND) on the incidence of Down's Syndrome (DS), but the results have varied widely. The impact of PND (reduction in the birth rate of chromosomally abnormal neonates) is related to utilization rates but quantitative estimates of this have not been established. In a three-year (1981–1983) total population study from Queensland, Australia, we present results to measure the impact of a voluntary PND programme on the birth incidence of DS, and also other chromosomally abnormal births. Utilization rates for the PND service were 15·5 per cent in that population of mothers 35 years and over. Numbers and rates of all cases of chromosomal abnormalities are presented, subclassified by type of diagnosis–-either by PND or by clinical diagnosis after birth. For the total population, 7·3 per cent of cases of DS were detected prenatally, and 15·4 per cent of all chromosome abnormalities. (A method for measuring the impact of PND is described.) Using this in conjunction with our demographic data, we estimate that with a 15 per cent utilization rate of PND by older mothers, 14 per cent of DS births can be prevented in this age group, or a 5 per cent overall reduction can be achieved if mothers of all ages are considered. One index–-the ratio of the percentage of DS births which are preventable compared with the population utilization rates of PND–-has potential for widespread use. Queensland data for this ratio is 0·34, a figure consistent with that from other studies. Thus a 3·5 per cent drop in the overall DS birth rate may be expected for each 10 per cent increase in the utilization rates of PND for mothers of 35 years and over. A diagram is presented which may serve as a model for improved data collection and better impact estimates in the future.     

Video recordings of prey capture behaviour and associated electric organ discharge of Torpedo marmorata (Chondrichthyes)

The results of an analysis of 16 laboratory records of Torpedo marmorata Risso attacks are presented: when a fish swims near a T. marmorata at rest, the latter jumps and simultaneously immobilizes the prey by its electric organ discharge (EOD). A water stream is used to direct the paralysed prey beneath its disc before swallowing. The attack is made if the prey swims at short distance ( 4 cm); height and direction of the jump are related to the position of the prey. The EOD, interrupted during the jump, reappears when the prey moves under the disc of T. marmorata, and ceases before swallowing. The strength of the EOD is sufficient to break the vertebral column of the prey. The possible receptor organs involved in this behaviour are presumed to be lateral line organs and touch detectors: the former to localize the prey before the jump, the latter to detect it under the disc. Evolutionary convergence of the prey capture behaviour of Torpedo, Malapterurus, and Electrophorus is also discussed.Supported by Research Grant No. 659440 from the Direction de Recherches et Moyens d'Essais (D.R.M.E.) to Dr. T. Szabo.Dr. Bauer's stay in France was sponsored by a N.A.T.O. and a D.F.G. research fellowship.     

The evolution of uniparental transmission of fungal symbionts in fungus-growing termites (Macrotermitinae)

Mutualistic associations between different organisms are theoretically expected when the interests of independently reproducing units are aligned to form a single reproductive unit. This alignment does not come about easily, because models show that hosts and symbionts can be in conflict over the transmission of symbionts. Selection will favour hosts that are able to limit genetic variation of symbionts, for example by enforcing uniparental vertical transmission, while symbionts will be selected to disperse independently of the host. A crucial factor determining the evolution and elaboration of symbiotic relationships is therefore who controls the transmission of symbionts. In the fungus-growing termites (Macrotermintinae) horizontal transmission seems to be the rule as the termites normally acquire their cultivated fungus (Termitomyces) from the environment. In spite of this general pattern, uniparental, vertical transmission has evolved in two unrelated Macrotermitinae genera, where only one sex of the two primary reproductives carries asexual spores from the fungal comb of its parent colony to inoculate the new fungus comb. Remarkably, symbiont transmission is exclusively paternal in Macrotermes bellicosus, whereas symbionts are maternally inherited in all Microtermes species studied so far. Thus, in Macrotermitinae horizontal transmission is the ancestral state with two independent origins to uniparental, vertical transmission. This is in contrast to fungus-growing ants where uniparental, vertical transmission is the rule. Causes and consequences of this difference are further discussed. Despite this fundamental difference both groups evolved a similar symbiosis that is probably the key for their ecological success: the fungus-growing ants in the neotropics and the fungus-growing termites in the paleotropics.     

Loss of PM2.5 nitrate from filter samples in central California

Evaporative loss of particulate matter (with aerodynamic diameter < 2.5 microm, [PM2.5]) ammonium nitrate from quartz-fiber filters during aerosol sampling was evaluated from December 3, 1999, through February 3, 2001, at two urban (Fresno and Bakersfield) and three nonurban (Bethel Island, Sierra Nevada Foothills, and Angiola) sites in central California. Compared with total particulate nitrate, evaporative nitrate losses ranged from < 10% during cold months to > 80% during warm months. In agreement with theory, evaporative loss from quartz-fiber filters in nitric acid denuded samplers is controlled by the ambient nitric acid-to-particulate nitrate ratio, which is determined mainly by ambient temperature. Accurate estimation of nitrate volatilization requires a detailed thermodynamic model and comprehensive chemical measurements. For the 14-month average of PM2.5 acquired on Teflon-membrane filters, measured PM2.5 mass was 8-16% lower than actual PM2.5 mass owing to nitrate volatilization. For 24-hr samples, measured PM2.5 was as much as 32-44% lower than actual PM2.5 at three California Central Valley locations.