A cost-benefit analysis of a population screening programme for neural tube defects

Population screening for neural tube defects is possible by measuring maternal serum alpha-fetoprotein levels with appropriate follow-up as required. British Columbia has approximately 39 000 births annually and the incidence of neural tube defects is 1–55 per 1000 births (0–94 per 1000 livebirths). Results from a cost-benefit analysis suggest that the outlined screening programme would be cost-beneficial for British Columbia. Other important factors essential to consider before instituting a population screening programme are discussed.     

Ultrasonographic diagnosis of a fetal abdominal mass: A case of a mesenchymal liver hamartoma and a review of the literature

A case of a prenatally recognized hepatic mesenchymal hamartoma is presented and the literature reviewed. These tumors are benign and usually present in early infancy with symptoms that are related to the mass effect on adjacent organs. Radiologic methods used in the past to image this tumor include angiography and ultrasound. However, there is no specific radiologic finding, and, therefore, the diagnosis is usually made during surgery. Once the tumor is removed, the prognosis is generally good. With the increasing use of high resolution ultrasound in prenatal diagnosis, this rare tumor should be considered in the differential diagnosis of any multicystic mass found in the fetal abdomen. The recognition of a mass should then alert the physician to the need for early neonatal intervention.     

A summary of environmental legislation targeting disposable diapers and review of related literature

In recent years state and local governments, as well as private citizens, have become very concerned about the mounting solid waste disposal problem facing our nation. Special concern has been expressed over the presence of disposable diapers in the solid waste stream. Responding to the concerns, legislators in at least 25 states proposed actions regarding disposable diapers between 1990 and 1992. Several factors contributed to the number of legislative proposals regarding disposable diapers over the past few years. First was the public's and legislators' misconception about the contribution of disposable diapers to the solid waste stream. Second was an erroneous assumption held by the public and some legislators that biodegradation readily occurs in landfills. Third was the desire to increase demand for agricultural products by requiring the use of degradable products. These contributing factors and other issues surrounding the proposal and passage of environmental legislation pertaining to disposable diapers are presented in this paper and the relevant literature is summarized. To provide the necessary context, the paper contains a review of the literature concerning disposable diapers, their composition and usage; and their environmental impact and fate and a comparison of their performance and cost to those of cloth diapers.     

Interspecific attractiveness of structures built by courting male fiddler crabs: experimental evidence of a sensory trap

Male fiddler crabs Uca musica sometimes build sand hoods and male Uca beebei sometimes build mud pillars next to their burrows to which they attract females for mating. Mate-searching females preferentially approach these structures and subsequently mate with structure builders. Here we show that the preference for structures is not species-specific and argue that it may not have evolved for mate choice. When not near burrows, many species of fiddler crabs approach and temporarily hide near objects, suggesting that hoods and pillars may attract females because they elicit this general predator-avoidance behavior. To test this sensory trap hypothesis we individually released female U. musica, U. beebei and Uca stenodactylus, a non-builder, in the center of a circular array of empty burrows to which we added hoods and pillars and then moved a model predator toward the females. All species ran to structures to escape the predator and the two builders preferred hoods. Next, we put hood replicas on male U. beebei burrows and pillar replicas on male U. musica burrows. When courted, females of both species preferentially approached hoods as they did when chased with a predator. However, males of both species with hoods did not have higher mating rates than males with pillars perhaps because hoods block more of a male's visual field so he sees and courts fewer females. Sexual selection may often favor male signals that attract females because they facilitate general orientation or navigation mechanisms that reduce predation risk in many contexts, including during mate search.     

Fetal liver alanine: Glyoxylate aminotransferase and the prenatal diagnosis of primary hyperoxaluria type 1

Primary hyperoxaluria type 1 (PH1) is caused by a deficiency of the hepatic peroxisomal enzyme alanine: glyoxylate aminotransferase (AGT, EC 2.6.1.44) (Danpure and Jennings, FEBS Lett., 201 , 20–24, 1986). The activity of AGT has been measured in fetal livers of gestational age 14–21 weeks. Activity increases up to 17 weeks and then levels off between 17 and 21 weeks. At this time, the mean AGT activity is about 30 per cent of the mean normal postnatal level. As in adult liver, the AGT enzyme activity and the AGT immunoreactive protein are peroxisomal. Prenatal diagnosis has been performed by measuring AGT enzyme activity and immunoreactive AGT protein on liver biopsies from two fetuses at risk for primary hyperoxaluria type 1. One was unaffected and one was affected.     

Amylo-1,6-glucosidase activity in cultured cells: A deficiency in type III glycogenosis with prenatal studies

Deficiency of amylo-1,6–glucosidase activity was expressed in parallel in liver and skin fibroblasts from a patient with type III glycogenosis. In crude extracts of control liver and muscle, amylo-1, 6–glucosidase (M.W. 164000) was identified by immunoprecipitation; no cross-reacting material was found in the patient's liver. Assay of amylo-1,6–glucosidase activity in cultured skin fibroblasts from the affected family revealed less than 10 per cent of control value in mutant homozygous cells whereas in cells from the parents, activity was reduced to 40–60 per cent of the control value. Activity in cultured amniotic fluid cells was similar to that of control fibroblasts. In cultured amniotic fluid cells obtained during the mother's subsequent pregnancy, the normal amylo–1,6–glucosidase activity measured, predicted correctly the outcome of this pregnancy prior to the 20th week of gestation.     

Avifaunal responses to fire in southwestern montane forests along a burn severity gradient.

The effects of burn severity on avian communities are poorly understood, yet this information is crucial to fire management programs. To quantify avian response patterns along a burn severity gradient, we sampled 49 random plots (2001-2002) at the 17351-ha Cerro Grande Fire (2000) in New Mexico, USA. Additionally, pre-fire avian surveys (1986-1988, 1990) created a unique opportunity to quantify avifaunal changes in 13 pre-fire transects (resampled in 2002) and to compare two designs for analyzing the effects of unplanned disturbances: after-only analysis and before-after comparisons. Distance analysis was used to calculate densities. We analyzed after-only densities for 21 species using gradient analysis, which detected a broad range of responses to increasing burn severity: (I) large significant declines, (II) weak, but significant declines, (III) no significant density changes, (IV) peak densities in low- or moderate-severity patches, (V) weak, but significant increases, and (VI) large significant increases. Overall, 71% of the species included in the after-only gradient analysis exhibited either positive or neutral density responses to fire effects across all or portions of the severity gradient (responses III-VI). We used pre/post pairs analysis to quantify density changes for 15 species using before-after comparisons; spatiotemporal variation in densities was large and confounded fire effects for most species. Only four species demonstrated significant effects of burn severity, and their densities were all higher in burned compared to unburned forests. Pre- and post-fire community similarity was high except in high-severity areas. Species richness was similar pre- and post-fire across all burn severities. Thus, ecosystem restoration programs based on the assumption that recent severe fires in Southwestern ponderosa pine forests have overriding negative ecological effects are not supported by our study of post-fire avian communities. This study illustrates the importance of quantifying burn severity and controlling confounding sources of spatiotemporal variation in studies of fire effects. After-only gradient analysis can be an efficient tool for quantifying fire effects. This analysis can also augment historical data sets that have small samples sizes coupled with high non-process variation, which limits the power of before-after comparisons.     

Stream ecosystem response to limestone treatment in acid impacted watersheds of the Allegheny Plateau.

Restoration programs are expanding worldwide, but assessments of restoration effectiveness are rare. The objectives of our study were to assess current acid-precipitation remediation programs in streams of the Allegheny Plateau ecoregion of West Virginia (USA), identify specific attributes that could and could not be fully restored, and quantify temporal trends in ecosystem recovery. We sampled water chemistry, physical habitat, periphyton biomass, and benthic macroinvertebrate and fish community structure in three stream types: acidic (four streams), naturally circumneutral (eight streams), and acidic streams treated with limestone sand (eight streams). We observed no temporal trends in ecosystem recovery in treated streams despite sampling streams that ranged from 2 to 20 years since initial treatment. Our results indicated that the application of limestone sand to acidic streams was effective in fully recovering some characteristics, such as pH, alkalinity, Ca2+, Ca:H ratios, trout biomass and density, and trout reproductive success. However, recovery of many other characteristics was strongly dependent upon spatial proximity to treatment, and still others were never fully recovered. For example, limestone treatment did not restore dissolved aluminum concentrations, macroinvertebrate taxon richness, and total fish biomass to circumneutral reference conditions. Full recovery may not be occurring because treated streams continue to drain acidic watersheds and remain isolated in a network of acidic streams. We propose a revised stream restoration plan for the Allegheny Plateau that includes restoring stream ecosystems as connected networks rather than isolated reaches and recognizes that full recovery of acidified watersheds may not be possible.     

Dominance and reproductive behavior of wild house mice in a seminatural environment correlated with T-locus genotype

Summary Behavior of mice whose T-locus genotype was either +/+ or +/t was observed in a seminatural environment. Heterozygous females were less likely to be dominant, less likely to go into behavioral estrus, and less likely to become pregnant than were +/+ females. The relative fitness of +/t as compared with +/+ females was 0.32:1.00. In contrast, +/t males produced 35% more young than did +/+ males. The higher fitness of +/t males was primarily due to a greater production of young on the part of +/t as compared with +/+ subordinate males. Little evidence was found under these naturalistic conditions, of non-random mating with respect to T-locus genotype. The indication of overdominance for +/t males makes it unlikely that heterozygote disadvantage will be sufficient to account for the frequency of t-alleles in natural populations.