Social capital and transaction costs in millet markets.

In sub-Saharan Africa, transaction costs are believed to be the most significant barrier that prevents smallholders and farmers from gaining access to markets and productive assets. In this study, we explore the impact of social capital on millet prices for three contrasted years in Senegal. Social capital is approximated using a unique data set on mobile phone communications between 9 million people allowing to simulate the business network between economic agents. Our approach is a spatial equilibrium model that integrates a diversified set of data. Local supply and demand were respectively derived from remotely sensed imagery and population density maps. The road network was used to establish market catchment areas, and transportation costs were derived from distances between markets. Results demonstrate that accounting for the social capital in the transaction costs explained 1-9% of the price variance depending on the year. The year-specific effect remains challenging to assess but could be related to a strengthening of risk aversion following a poor harvest.

Strategic behavior and marriage payments: theory and evidence from Senegal.

This article proposes an original theory of marriage payments based on insights gained from firsthand information collected in the Senegal River valley. This theory postulates that decisions about the bride-price, which are made by the bride's father, take into account the likely effects of the amount set on the risk of ill-treatment of the wife and the risk of marriage failure. Based on a sequential game with three players (the bride's father, the husband, and the wife) and a matching process, it leads to a number of important predictions that are tested against Senegalese data relating to bride-prices and various characteristics of women. The empirical results confirm that parents behave strategically by keeping bride-prices down so as to reduce the risk of marriage failure for their daughters. Other interesting effects on marriage payments and the probability of separation are also highlighted, stressing the role of the bride's bargaining power in her own family.

Relationships between vitamin A and PCBs in grey seal mothers and pups during lactation.

A previous study has shown a simultaneous increase of vitamin A and PCBs in grey seal (Halichoerus grypus) milk at late lactation (Debier et al., 2004). Here we sought to understand this unexpected relationship by comparing the dynamics of vitamin A and PCBs in the different tissue compartments of transfer. Lactating grey seals and their pups were sampled longitudinally in Scotland during the 2006 breeding season. As blubber reserves decreased, concentrations of vitamin A and PCBs increased during lactation in the inner layer of maternal blubber. A concomitant rise was observed in milk and consequently in the serum of suckling pups. The similar dynamics of vitamin A and PCBs in milk and inner blubber suggest a common mechanism of mobilisation from maternal body stores and transfer into the milk. A panel data analysis highlighted a negative impact of PCBs in milk and pup serum on vitamin A status in pup serum.