Variation in jaw size during evolution has been crucial for the adaptive radiation of vertebrates, yet variation in jaw size during development is often associated with disease. To test the hypothesis that early developmental events regulating neural crest (NC) progenitors contribute to species-specific differences in size, we investigated mechanisms through which two avian species, duck and quail, achieve their remarkably different jaw size. At early stages, duck exhibit an anterior shift in brain regionalization yielding a shorter, broader, midbrain. We find no significant difference in the total number of pre-migratory NC; however, duck concentrate their premigratory NC in the midbrain, which contributes to an increase in size of the post-migratory NC population allocated to the mandibular arch. Subsequent differences in proliferation lead to a progressive increase in size of the duck mandibular arch relative to that of quail. To test the role of pre-migratory NC progenitor number in regulating jaw size, we reduced and augmented NC progenitors. In contrast to previous reports of regeneration by NC precursors, we find that neural fold extirpation results in a loss of NC precursors. Despite this reduction in their numbers, post-migratory NC progenitors compensate, producing a symmetric and normal-sized jaw. Our results suggest that evolutionary modification of multiple aspects of NC cell biology, including NC allocation within the jaw primordia and NC-mediated proliferation, have been important to the evolution of jaw size. Furthermore, our finding of NC post-migratory compensatory mechanisms potentially extends the developmental time frame for treatments of disease or injury associated with NC progenitor loss.

Container-based sanitation (CBS) – in which wastes are captured in sealable containers that are then transported to treatment facilities – is an alternative sanitation option in urban areas where on-site sanitation and sewerage are infeasible. This paper presents the results of a pilot household CBS service in Cap Haitien, Haiti. We quantify the excreta generated weekly in a dense urban slum,(1) the proportion safely removed via container-based public and household toilets, and the costs associated with these systems. The CBS service yielded an approximately 3.5-fold decrease in the unmanaged share of faeces produced, and nearly eliminated the reported use of open defecation and “flying toilets” among service recipients. The costs of this pilot small-scale service were higher than those of large-scale waterborne sewerage, but economies of scale have the potential to reduce CBS costs over time. The paper concludes with a discussion of planning and policy implications of incorporating CBS into the menu of sanitation options for rapidly growing cities.

Household-level container-based sanitation (CBS) services may help address the persistent challenge of providing effective, affordable sanitation services for which low-income urban households are willing to pay. Little is known, however, about user perceptions of and demand for household CBS services. This study presents the results of a pilot CBS service programme in Cap Haitien, Haiti. One hundred and eighteen households were randomly selected to receive toilets and a twice-weekly collection service. After three months, changes in these households’ satisfaction with their sanitation situation, along with feelings of pride, modernity and personal safety, were compared to 248 households in two comparison cohorts. Following the service pilot, 71 per cent of participating households opted to continue with the container-based sanitation service as paying subscribers. The results from this study suggest that, in the context of urban Haiti, household CBS systems have the potential to satisfy many residents’ desire for safe, convenient and modern sanitation services.

Kigali, Rwanda lacks a centralized sewer system, which leaves residents to choose between on-site options; the majority of residents in informal settlements use pit latrines as their primary form of sanitation. When their pits fill, the pits are either sealed, or emptied; emptying is often done by hand and then dumped in the environment, putting the residents and the broader population at risk of infectious disease outbreaks. In this paper, we used revealed and stated preference models to: (1) estimate the demand curve for improved emptying services; and, (2) evaluate household preferences and the willingness to pay (WTP) for different attributes of improved emptying services. We also quantify the costs of improved service delivery at different scales of production. The study included 1167 households from Kigali, Rwanda across 30 geographic clusters. Our results show that, at a price of US$79 per pit, 15% of all the pits would be emptied by improved emptying services, roughly the current rate of manual emptying. Grouping empties by neighborhood and ensuring that each truck services an average of four households per day could reduce the production costs to US$44 per empty, ensuring full cost coverage at that price. At a lower price of US$24, we estimate that the sealing of pits might be fully eliminated, with full coverage of improved emptying services for all pits; this would require a relatively small subsidy of US$20 per empty. Our results show that households had strong preferences for fecal sludge (FS) treatment, formalized services (which include worker protections), and distant disposal. The results from the study indicate a few key policies and operational strategies that can be used for maximizing the inclusion of low-income households in safely managed sanitation services, while also incorporating household preferences and participation.

SynopsisLiving near or migrating to areas at high risk for wildfires may result in health consequences and increased disparities for pregnant people and their children.