Data from: Nonrandom dispersal drives phenotypic divergence within a bird population

Gene flow through dispersal has traditionally been thought to function as a force opposing evolutionary differentiation. However, directional gene flow may actually reinforce divergence of populations in close proximity. This study documents the phenotypic differentiation over more than two decades in body size (tarsus length) at a very short spatial scale (1.1 km) within a population of pied flycatchers Ficedula hypoleuca inhabiting deciduous and coniferous habitats. Unlike females, males breeding in the deciduous forest were consistently larger than those from the managed coniferous forest. This assortment by size is likely explained by preset habitat preferences leading to dominance of the largest males and exclusion of the smallest ones toward the nonpreferred coniferous forest coupled with directional dispersal. Movements of males between forests were nonrandom with respect to body size and flow rate, which might function to maintain the phenotypic variation in this heritable trait at such a small spatial scale. However, a deeply rooted preference for the deciduous habitat might not be in line with its quality due to the increased levels of breeding density of hole-nesting competitors therein. These results illustrate how eco-evolutionary scenarios can develop under directional gene flow over surprisingly small spatial scales. Our findings come on top of recent studies concerning new ways in which dispersal and gene flow can influence microevolution.

传统观点认为，通过扩散（dispersal）实现的基因流（gene flow）是对抗演化分化的演化动力。然而，定向基因流（directional gene flow）实则可能强化邻近种群间的分化。本研究记录了栖息于落叶林与针叶林生境中的斑姬鹟（*Ficedula hypoleuca*）种群内，二十余年间在极短空间尺度（1.1 km）下的体型（body size，跗跖长度(tarsus length)）表型分化（phenotypic differentiation）情况。与雌性个体不同，在落叶林繁殖的雄性个体体型始终大于人工管理针叶林内的繁殖雄性。这种体型分异的分布模式，大概率可通过预设生境偏好得到解释：体型最大的雄性占据优势地位，将体型最小的个体排挤至非偏好的针叶林生境，结合定向扩散共同促成该格局。雄性在林区间的移动在体型与扩散速率（flow rate）上均呈现非随机性，这一现象或可在如此小的空间尺度下维持该可遗传性状（heritable trait）的表型变异（phenotypic variation）。然而，对落叶林生境的根深蒂固的偏好，或许与其实际质量并不匹配——因为该生境内洞巢竞争者（hole-nesting competitors）的繁殖密度有所升高。本研究结果阐明了生态-演化动态（eco-evolutionary scenarios）如何在定向基因流作用下，于出人意料的小空间尺度下形成。我们的研究成果为近期围绕‘扩散与基因流影响微演化（microevolution）的新途径’的相关研究提供了新的实证支撑，进一步丰富了该领域的认知。