Gene flow and population structure of a common agricultural wild species (Microtus agrestis) under different land management regimes

The impact of landscape structure and land management on dispersal of populations of wild species inhabiting the agricultural landscape was investigated focusing on the field vole (Microtus agrestis) in three different areas in Denmark using molecular genetic markers. The main hypotheses were the following: (i) organic farms act as genetic sources and diversity reservoirs for species living in agricultural areas and (ii) gene flow and genetic structure in the agricultural landscape are influenced by the degree of landscape complexity and connectivity. A total of 443 individual voles were sampled within 2 consecutive years from two agricultural areas and one relatively undisturbed grassland area. As genetic markers, 15 polymorphic microsatellite loci (nuclear markers) and the central part of the cytochrome-b (mitochondrial sequence) were analysed for all samples. The results indicate that management (that is, organic or conventional management) was important for genetic population structure across the landscape, but that landscape structure was the main factor shaping gene flow and genetic diversity. More importantly, the presence of organically managed areas did not act as a genetic reservoir for conventional areas, instead the most important predictor of effective population size was the amount of unmanaged available habitat (core area). The relatively undisturbed natural area showed a lower level of genetic structuring and genetic diversity compared with the two agricultural areas. These findings altogether suggest that political decisions for supporting wildlife friendly land management should take into account both management and landscape structure factors.

本研究以丹麦三个不同区域的田间田鼠（Microtus agrestis）为研究对象，采用分子遗传标记（molecular genetic markers），探究了景观结构与土地管理模式对栖息于农业景观中的野生物种种群扩散过程的影响。本研究提出两项核心假说：其一，有机农场可作为农业区域物种种群的遗传源与多样性储库；其二，农业景观中的基因流与遗传结构受景观复杂度及连通度的调控。研究连续两年共采集443只田鼠个体，采样区域涵盖两个农业区域与一处相对未受干扰的草原区域。针对所有样本，本研究分析了15个多态性微卫星位点（microsatellite loci，核标记（nuclear markers））以及细胞色素b（cytochrome-b）基因的中心区段（线粒体序列（mitochondrial sequence））。研究结果显示，管理方式（即有机或常规农业管理）对整个景观的种群遗传结构具有显著影响，但景观结构才是塑造基因流与遗传多样性的主导因素。更为关键的是，有机管理区域的存在并未为常规农业区域提供遗传储库；反之，影响有效种群规模的最重要预测因子为未受管理的可用栖息地（核心栖息地）的面积。相较两个农业区域，相对未受干扰的自然区域呈现出更低水平的遗传结构分化与遗传多样性。综上，支持野生动物友好型土地管理的政策决策，应同时兼顾土地管理方式与景观结构两类核心因素。