传统农业系统中的遗传多样性：存留机制与生态适应

Traditional agriculture systems are known to host large genetic diversity, but the mechanisms that underlies how the genetic diversity is maintained, and whether the genetic diversity help adapt to local conditions are poorly understood. The overall goal of this grant project is to examine how genetic diversity of indigenous carps originated and evolved in rice field are maintained in the Globally Important Agriculture Heritage System (GIAHS) -- “rice-fish system” at Zhejiang province and “rice-fish-duck system” at Guizhou province. The central hypotheses of this project are: (1) large volume of parental carps that scattered in small household farmers, and parental carp exchange driven by farmer connectivity may contribute to high genetic diversity maintenance in both of the GIAHSs; (2) the genetic variation may help the carps to adapt to different environment and complementary use limited resources in rice field, which, in turn, help maintain genetic diversity. The project plans to: (1) to characterize the pattern of genetic diversity of the indigenous common carp by sampling from different geographical locations (natural villages as sampling units) and using molecular methods; (2) to quantify the gene flow, landscape isolation and farmer connectivity among geographical locations, numbers of parental carps held by farmers; (3) to test how farmer connectivity and numbers of parental carps affect the gene flow and heterozygosity maintenance by using models of population viability analysis; (3) to examine ecological differences of small populations by monitoring in situ and how a genetic diversified carp population may result in higher efficiency of resource use and population productivity by field controlled experiment. The project will reveal the role of traditional agricultural systems as conservators in maintaining genetic diversity. Understanding how tratitonal agriculture systems preserve genetic diversity help design methods for genetic diversity preservation and help design sustainable agriculture by integrating traditional knowledge with modern technologies.

传统农业系统孕育着丰富的遗传资源，但传统农业系统中遗传多样性的维持机理及生态适应性有待揭示。本项目拟以全球重要农业文化系统“青田稻鱼共生系统”和 “从江稻鱼鸭共生系统”保育的“土著田鱼”为例，计划：（1）研究田鱼遗传多样性在传统农业系统的分布格局和基因型类群特征；（2）通过地理隔离与农户连接、田鱼亲本数量和自交率、种质交换频率和基因流等的分析，验证“地理隔离是多样化类群形成的影响因素，而农户连接和大样本亲本数量是遗传多样性（杂合度）维持的重要机理”的假说。（3）通过原位观测和田间受控实验剖析种群遗传多样性与生态适应性的关系，验证“种群内遗传的多样性可能会带来生态适应的分化，有利于种群内个体之间互补利用稻田食物资源，从而提高种群的适合度”的假说。结果将揭示传统农业系统维持遗传多样性的机理，并阐明遗传多样性与种群生态适应性的关系，可为农业系统如何保护和利用遗传多样性提供参考。

传统农业系统孕育着丰富的遗传资源，但传统农业系统中遗传多样性的维持机理及生态适应性有待揭示。本项目以分布于我国南方山丘区传统稻鱼系统中田鱼种群为范例，研究（1）田鱼的遗传多样性及分布格局；（2）传统农业统维持田鱼遗传多样性的机理；（3）稻田环境下田鱼的生态适应性；验证“地理隔离是田鱼多样化种群形成的因素，而农户连接度和大样本亲本数量是遗传多样性（杂合度）维持的重要机理”的假说。研究采用分子生物学和景观遗传学方法、稳定性同位素和摄像技术开展研究。经4年研究，完成了项目计划的研究内容和目标, 重要研究进展如下：（1）通过线粒体D-loop基因设计引物进行的遗传类群分析发现，我国南方山丘区传统稻鱼系统分布有9个形态明显差异田鱼地方种群，且均保留有较高的遗传多样性，期望杂合度He（0.78±0.04）明显高于养殖普通鲤鱼（Cyprinus carpio）的平均值（0.69±0.07）。对不同地区田鱼种群的遗传结构进行分子方差分析（AMOVA）表明，南方地区田鱼的遗传变异主要位于种群内（92%，P=0.001），种群间遗传变异较小（8%，P=0.001）。（2）景观遗传学方法揭示农户连接（farmer connectivity）对景观区域内田鱼基因流的促进，种群生存力分析（population viability analysis）进一步揭示农户连接促进的基因流使得土著田鱼的遗传多样性（He）长时间维持较高的水平，大量连接着的农户保留鱼种是传统农业系统田鱼多样性维持的重要机制。（3）基于地标点的几何形态测量（landmark-based geometric morphometric analysis）显示田鱼形态表型的多样性；连续摄像观察发现，表型不同的田鱼取食行为著显差异；稳定性同位素(15N和13C)的分析表明，不同表型的田鱼对稻田资源的利用格局明显不同，田间实验进一步表明，田鱼表型间的这些差异有利于种群适合度的提高，进而有利于田鱼群体遗传多样性的维持。上述研究结果对了解传统农业在遗传多样性的保育效应和机理、阐明遗传多样性与生态适应性的关系有重要科学价值，也为农业系统如何保持和利用遗传多样提供科学依据。