Maintenance versus Growth: Investigating the Costs of Immune Activation Among Children in Lowland Bolivia T.W. McDade, 1,2 * V. Reyes-Garcı´a, 3,4 S. Tanner, 5 T. Huanca, 6 and W.R. Leonard 1 1 Department of Anthropology, Northwestern University, Evanston, IL 60208 2 Cells to Society (C2S): The Center on Social Disparities and Health, Institute for Policy Research, Northwestern University, Evanston, IL 60208 3 ICREA and Institut de Cie `ncia i Tecnologia Ambientals, Universitat Auto `noma de Barcelona, 08193 Bellatera, Barcelona, Spain 4 Sustainable International Development Program, Heller School for Social Policy and Management, Brandeis University, Waltham, MA 02454 5 Department of Anthropology, University of Georgia, Athens, GA 30606 6 Centro Boliviano de Desarrollo y de Investigacio ´n Socio Integral (CBIDSI), San Borja, Beni, Bolivia KEY WORDS ecological immunology; human growth and development; acute phase response; life history theory; infectious disease; Amazonia ABSTRACT Immune function is a central component of maintenance effort, and it provides critical protection against the potentially life threatening effects of patho- gens. However, immune defenses are energetically ex- pensive, and the resources they consume are not avail- able to support other activities related to growth and/or reproduction. In our study we use a life history theory framework to investigate tradeoffs between maintenance effort and growth among children in a remote area of Amazonian Bolivia. Baseline concentrations of C-reactive protein (CRP) were measured in 309 2- to 10-year olds as an indicator of immune activation, and height was measured at baseline and three months later. Elevated CRP at baseline predicts smaller gains in height over the subsequent three months, with the costs to growth particularly high for 2- to 4-year olds and for those with low energy reserves (in the form of body fat) at the time of immunostimulation. These results provide evidence for a significant tradeoff between investment in immunity and growth in humans, and highlight an important physi- ological mechanism through which maintenance effort may have lasting effects on child growth and development. Am J Phys Anthropol 136:478–484, 2008. V V C 2008 Wiley-Liss, Inc. Life history theory begins with the premise that organisms attempt to allocate limited resources to pri- mary life functions related to growth, reproduction, and maintenance in ways that optimize reproductive fitness (Stearns, 1992; Charnov, 1993). The immune system is an essential component of maintenance effort, playing central roles in cellular renewal and repair and in defending against the damaging—and potentially life threatening—effects of pathogenic agents (McDade, 2003). Immune defenses are energetically expensive, and resources consumed by immune processes are not avail- able to support investments in activities related to growth and/or reproduction. Indeed, recent work in eco- logical immunology has highlighted the important roles that pathogen pressure and antipathogen defenses play in contributing to life history variation in a range of non- human populations (Sheldon and Verhulst, 1996; Loch- miller and Deerenberg, 2000). In our study we use a life history framework to investigate costs to growth associ- ated with immune activation among children in a remote area of Amazonian Bolivia. Attempts to evaluate life history tradeoffs in humans are challenged by the need to control for individual dif- ferences in resources that fuel investments in growth, reproduction, and maintenance. For example, children with reliable access to energy-rich foods will have suffi- cient fuel for growth as well as an effective immune response to infection, whereas relatively undernourished children will exhibit poorer growth and impaired immu- nity. Simple correlations between growth and immune function may therefore reveal positive, rather than nega- tive, associations between investments in growth and immune function. While the expected life history tradeoff still operates at the individual level (for all individuals, energy applied to immunity cannot also be allocated to growth), we may not see the tradeoff at the level of the population. This is the problem of phenotypic correlation (Hill and Hurtado, 1996). A consideration of individual differences in phenotypic quality—both in terms of measurement and statistical analysis—is critical for a meaningful evaluation of life history tradeoffs in humans. In our study we attempt to address this issue by collecting data on a range of indi- vidual- and household-level factors that may shape phe- Grant sponsor: National Science Foundation; Grant numbers: BCS-0134225, BCS-0078801, BCS-0200767. *Correspondence to: Thomas W. McDade, Department of Anthro- pology, Northwestern University, 1810 Hinman Avenue, Evanston, IL 60208, USA. E-mail: t-mcdade@northwestern.edu Received 25 October 2007; accepted 8 February 2008 DOI 10.1002/ajpa.20831 Published online 26 March 2008 in Wiley InterScience (www.interscience.wiley.com). V V C 2008 WILEY-LISS, INC. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 136:478–484 (2008)