Doctoral Dissertation Improvement: Culture, Evolution and Immunity in Breastfeeding Ariaal Mothers and Infants

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

This project will test the trade-offs between mucosal immunity and life history traits in the cultural, disease and nutritional ecology of breastfeeding Ariaal mothers and infants of northern Kenya. Recent evolutionary theory has emphasized the impact of the transfer of non-genetic information between mother and child on adult phenotype, particularly the effects of prenatal nutrition on infant growth outcomes. The postnatal transfer of secretory immunoglobulin A (sIgA) via breastfeeding, however, offers new opportunities to explore the long-term effects of passive immunity. Breastfeeding is an ideal system for studying the transfer of immunity because it is highly influenced by cultural traditions, it provides life-long benefits, and because sIgA is specific to the diseases the mother has encountered in her environment. This research will evaluate the dynamics that govern this information transfer using insights from life history theory, addressing two questions: I) How does the maternal trade-off between current and future reproduction affect the transfer of immunoglobulins (specifically, secretory immunoglobulin A (sIgA)) between mother and infant via breastfeeding? and II) How does this maternal trade-off in investment affect the trade-offs infants face between growth and immune function (maintenance)? Within this framework, this project will also assess the impact of culture-specific breastfeeding practices and the local disease ecology on sIgA levels in both mothers and infants. Two hundred and forty breastfeeding Ariaal mother-infant pairs will be asked to participate in an interview, anthropometric measurements, and biomarker collection. Saliva and breast milk will be dried on filter paper and analyzed for sIgA, a field-friendly method currently under development by the co-PI. Evolutionary hypotheses will be analyzed using multivariate linear regression, adjusting for the pair's cultural and disease ecology. This project proposes that life history trade-offs can illuminate patterns of breastfeeding and immunity in both mothers and infants. Within this evolutionary framework, it also considers how the breastfeeding system adapts to the local cultural and disease ecology. Passive immunity through breastfeeding is ideal to study the role of maternal effects in human populations because transfer of pathogen-specific antibodies from the mother's gut and culture-specific weaning behaviors that modify breast milk intake can influence offspring phenotype. This anthropological research has implications for health interventions targeting breastfeeding and infant mortality by testing the importance of the shared mucosal immunity between mother and infant, illuminating cultural barriers to breastfeeding interventions, and promoting the application of field-friendly methods of health assessment.