A Constructed Niche: An Example of Gene- Culture Coevolution (?) Cholesterol Metabolism - Maize Culture

H ünemeier et al PLoS ONE 7: e38862 (10 pp) Niche Construction Cultures modify their environments Alters natural selection on individuals (and associated species) Hypothesis: Cultural organism (human) co-directs its own evolution

H ünemeier et al PLoS ONE 7: e38862 (10 pp) America: last continent colonized by modern humans app. 15,000 YBP Adaptation to novel environments (?) Imply rapid evolution in human populations Find some correlations between allelic distributions and subsistence modes in Native Americans

Genes and Subsistence Cultures 230Cys allele Variant found only in Native Americans/mestizos Previously known: Lowers HDL (good) cholesterol Increases comorbidityBUT Increases energy efficiency/storage capacity when food scarce

230Cys Historically Data: Directional selective sweep in some populations Hypothesis: Survival during periods of famine Niche construction: Selection contingent of agriculture relying heavily on maize monoculture; secondarily associated with disease in contemporary environments

H ünemeier et al PLoS ONE 7: e38862 (10 pp) 230Cys allele frequencies Amerindian populations (1905 individuals) Mexico through S America Clusters: Mesoamerican agriculture (16 populations) Andean agriculture (7 populations) S American hunter-gatherer (27 populations)

Results: Allele Frequencies Mesoamerican agriculture differs significantly from other 2 populations S America: No significant difference between agriculturists and hunter-gatherers Not just agriculture vs hunter-gatherer (narrower vs broader diet selection) Agricultural diet in Mesoamerica: Increase in allele frequency

Results: Allele Age 230Cys variant 2 methods: 12K to 19K YBP (America colonized 15K YBP) 7,540 YBP Both estimates: American origin for allele 230Cys apparently favored by selection

Results: Frequency variation in Mesoamerica Positive correlation: Allele and Time since Zea maize introduced

Maize Culture Maize most important native crop in America Mesoamerican villages began with maize domestication Originated in SW Mexico and spread with transition to sedentary life (pollen records, pottery history)

Maize Culture Mesoamericans: Only ancients without domesticated herbivore Reliance on maize monoculture Mayan culture: App. 75% of calories from maize Production: highly variable among years – population densities increased Monoculture: Occasional famine Crop disease, poor storage

Maize Culture Monoculture: Occasional famine Crop disease, poor storage Perhaps Survival during famine favored allele that increased energy efficiency (some Dengue resistance) Historical advantage during food scarcity Today: Cholesterol (HDL) associated disease

Maize Culture Culture: Changed environment Narrow diet, single-crop reliance Concentration of people dependent on crop Temporally variable weather, crop disease Selection on New World allelic variant: survival Cultural niche changed natural selection on individuals