Evolutionary and food supply implications of ongoing maize domestication by Mexican campesinos

Maize evolution under domestication is a process that continues today. Case studies suggest that Mexican smallholder family farmers, known as campesinos, contribute importantly to this, but their significance has not been explicitly quantified and analyzed as a whole. Here we examine the evolutionary and food security implications of the scale and scope under which campesinos produce maize. We gathered official municipal-level data on maize production under rainfed conditions and identified campesino agriculture as occurring in municipalities with average yields of ≤ 3 t/ha. Environmental conditions vary widely in those municipalities and are associated with a great diversity of maize races, representing 85.3% of native maize samples collected in the country. We estimate that in those municipalities around 1.38 x 1011 genetically different individual plants are subjected to evolution under domestication each season. This implies that 5.24x108 mother plants contribute to the next generation with their standing genetic diversity and rare alleles. Such a large breeding population size also increases the total number of adaptive mutations that may appear and be selected for. We also estimate that campesino agriculture could potentially feed around 54.7 million people in Mexico. These analyses provide insights about the contributions of smallholder agriculture around the world.

驯化背景下的玉米演化进程至今仍在持续。现有案例研究表明，墨西哥的小农户家庭农场主——坎佩西诺农户（campesinos）对此进程做出了重要贡献，但目前尚未对其整体重要性开展明确量化与系统分析。本研究针对坎佩西诺农户开展玉米种植的规模与范围，探讨其对玉米演化及粮食安全的影响。我们收集了官方发布的雨养条件下玉米生产的市级层面数据，并将平均产量≤3吨/公顷的市域判定为坎佩西诺农业分布区域。上述市域的环境条件差异显著，且与丰富多样的玉米地方品种类群（maize races）紧密相关，其所覆盖的本土玉米样本占全国采集总量的85.3%。我们估算，在上述市域内，每个生长季约有1.38×10¹¹个遗传背景各异的个体植株处于驯化演化过程中。这意味着共有5.24×10⁸株母本植株通过自身固有的遗传多样性与稀有等位基因，为下一代种群贡献遗传物质。如此庞大的繁育种群规模，同时提升了潜在出现并被正向选择的适应性突变的总数量。此外我们估算，坎佩西诺农业可满足墨西哥约5470万人口的粮食需求。本研究的分析结果，为全球范围内小农户农业的贡献提供了全新的认知视角。