What is the real “price” of more prenatal screening and fewer diagnostic procedures? Costs and trade-offs in the genomic era

Any screening approach, including with cell-free DNA, will have an inferior detection rate compared with 100% diagnostic testing with chromosomal microarrays. Cell-free DNA-based screening, however, should not be seen as a threat to informed choice or maximising the benefits of diagnostic testing. Screening methods have become so much better that more women are now comfortable relying on such screening and do not need the certainty of a diagnostic test. This has not lead to a decline in detection of fetal chromosome abnormalities—in fact, we are now seeing historically high yields from prenatal screening. There are both economic and ethical consequences of offering universal diagnostic testing and abandoning the presumption of a normal infant in otherwise uncomplicated pregnancies. However, for some women, comprehensive information and diagnostic accuracy are important. Offering these women all options, with a careful and comprehensive explanation of the risks and benefits of each, results in outcomes that are best aligned with woman's preferences while at the same time requiring fewer diagnostic tests and lowering costs. It is one of the primary challenges of the modern era of prenatal testing to ensure that women receive sufficient information on which to make informed decisions.     

Quantitative threat analysis for management of an imperiled species: Chinook salmon (Oncorhynchus tshawytscha).

Chinook salmon (Oncorhynchus tshawytscha) have declined dramatically across the Pacific Northwest because of multiple human impacts colloquially characterized as the four "H's": habitat degradation, harvest, hydroelectric and other dams, and hatchery production. We use this conceptual framework to quantify the relative importance of major threats to the current status of 201 Chinook populations. Current status is characterized by two demographic indices: population density and trend. We employ path analytic models and information theoretic methods for multi-model inference. Our results indicate that dams most strongly affect variation in population density, while harvest and hatchery production most strongly affect variation in population trend. Comparable results arise when the sample size of the analysis is reduced to 22 Chinook populations within a smaller region typical of the scale at which salmon recovery planning is conducted. Results from these threat analyses suggest that recovery strategies targeting specific demographic indices, and those considering natural and human-mediated interdependencies of major threats, are most likely to succeed.     

Group-living in cliff swallows as an advantage in avoiding predators

Summary Cliff swallows (Hirundo pyrrhonota) in SW Nebraska, USA, nest in colonies and associate in groups away from their colonies. The degree to which group-living in this species affords advantages in the avoiding of predators was examined. The distance from the colony at which a snake predator was detected increased with colony size. In flocks away from the colonies, group vigilance increased, but the time that each individual spent vigilant decreased, with flock size. As a result, birds in large flocks had more time for preening and mud-gathering. Cliff swallows did not effectively mob predators and thus were unable to deter predators regardless of group size. Nesting within each colony was highly synchronous, but when the effects of ectoparasites on nesting success were removed, individuals nesting during the peak breeding period were no more successful than those nesting before or after the peak. This suggests that swamping of predators is unlikely in cliff swallow colonies. Nests at the edges of colonies were more likely to be preyed upon than nests nearer the center, suggesting that colonial nesting conferred some selfish herd benefits. Overall reproductive success did not vary with colony size. While cliff swallows receive some anti-predator benefits by living in groups, the avoidance of predators is probably not a major selective force for the evolution of coloniality in this species.     

The effect of selection treatments on <Emphasis Type=Italic>Mytilus edulis</Emphasis>, modifications of genetic and physiological characteristics

This study examined the effects of two selection treatments (elevated water temperature and air exposure) on the genetic and physiological characteristics of the juvenile marine mussel, Mytilus edulis (<10 mm). Genetic effects were measured on five allozymes and fitness assessed using physiological tests to estimate energy balance (scope for growth) as well as size, growth and survival. The in vitro treatments resulted in 48% mortality from an air exposure of 11 h at 27°C and 76% mortality from a 6-h exposure to 33°C water. Survivors (n = 1,152) of each treatment along with controls (n = 2,304) were measured and randomly placed in compartmentalized cages. Mussels were deployed to three bays in Prince Edward Island, Canada and monitored over a 10-month period. Initially, both of the treatments had an effect on mussel size and increased the heterozygosity of the surviving mussels. Physiological analyses after 3 months in the field showed that the two treated mussels showed lower metabolic rate that the control group. After 10 months in the field, the treated mussels were larger and had lower mortality than the untreated control mussels. Unexplained environmental interaction in each of the bays had an effect on allelic frequencies and heterozygosity. Overall, the results demonstrate that simple husbandry techniques can be used to increase the productivity of mussel seed and heterozygosity measures can be used to assess fitness. However, more field data is needed to determine the consistency of the increased productivity and if the increased productivity justifies the costs of a selective treatment. Furthermore, because the level of heterozygosity in juvenile mussel populations can vary considerably, both spatially and temporally, it may be effective as a warning of future natural mass mortality when overall heterozygosity levels are found to be low.     

Genetic Diversity in the Endangered Lily Harperocallis flava and a Close Relative, Tofieldia racemosa

We examined genetic diversity in 464 individuals of the monotypic lily Harperocallis flava in its two habitats (seepage bogs and a roadside right-of-way) and five populations of a co-occurring related lily, Tofieldia racemosa. The endangered H. flava, endemic to the Apalachicola lowlands of the Florida panhandle, was monomorphic for the 22 loci scored. In contrast, T. racemosa had a high proportion of polymorphic loci ( P_s = 68.2%; P_p = 47.7%) with moderate genetic diversity (   H_es = 0.134; H_ep = 0.114). Estimated gene flow was moderately high ( Nm = 2.07) for T. racemosa, with most (93%) of the total genetic diversity found within populations. Despite the low level of genetic divergence, some isolation by distance was detected among T. racemosa populations. Harperocallis flava and other species without discernable genetic variation pose special problems for conservation biologists because genetic criteria are not available for the development of ex situ and in situ conservation and management strategies.