Two estimates of the metabolic costs of antibody production in migratory shorebirds: low costs, internal reallocation, or both?

We measured the costs of mounting a humoral immune response using two novel antigens (tetanus and diphtheria) in two shorebird species (Scolopacidae): Red Knot (Calidris canutus, measured in autumn) and Ruff (Philomachus pugnax, measured in spring). Metabolic rate was measured during the preinjection phase, at the building phase of the primary immune response, and at peak secondary immune response by determining the oxygen consumption of the postabsorptive birds at rest. Confirming earlier studies, Red Knots and Ruffs responded with lower antibody titers to the diphtheria than to the tetanus antigen. Although Red Knots and Ruffs produced the same amounts of antibodies, Red Knots showed a significant 13% increase in basal metabolic rate (BMR) during the secondary antibody response, whereas Ruffs showed a 15%, but only marginally significant, reduction in BMR. The results from this study suggest that the energetic costs of an immune response may be small, but the "negative cost" in Ruffs hints at the possibility of resource reallocation and the concomitant difficulty of measuring such costs during "basal" metabolic rate measurements.     

Cascading costs:An economic nitrogen cycle

The chemical nitrogen cycle is becoming better characterized in terms of fluxes and reservoirs on a variety of scales. Galloway has demonstrated that reactive nitrogen can cascade through multiple ecosystems causing environmental damage at each stage before being denitrified to N2. We propose to construct a parallel economic nitrogen cascade (ENC) in which economic impacts of nitrogen fluxes can be estimated by the costs associated with each stage of the chemical cascade. Using economic data for the benefits of damage avoided and costs of mitigation in the Chesapeake Bay basin, we have constructed an economic nitrogen cascade for the region. Since a single tonne of nitrogen can cascade through the system, the costs also cascade. Therefore evaluating the benefits of mitigating a tonne of reactive nitrogen released needs to consider the damage avoided in all of the ecosystems through which that tonne would cascade. The analysis reveals that it is most cost effective to remove a tonne of nitrogen coming from combustion since it has the greatest impact on human health and creates cascading damage through the atmospheric, terrestrial, aquatic and coastal ecosystems. We will discuss the implications of this analysis for determining the most cost effective policy option for achieving environmental quality goals.