Candidate gene polymorphisms for behavioural adaptations during urbanization in blackbirds

Successful urban colonisation by formerly rural species represents an ideal situation in which to study adaptation to novel environments. We address this issue using candidate genes for behavioural traits that are expected to play a role in such colonisation events. We identified and genotyped 16 polymorphisms in candidate genes for circadian rhythms, harm avoidance, and migratory and exploratory behaviour in 12 paired urban and rural populations of the blackbird Turdus merula across the Western Palearctic. An exonic microsatellite in the SERT gene, a candidate gene for harm avoidance behaviour, exhibited a highly significant association with habitat type in an analysis conducted across all populations. Genetic divergence at this locus was consistent in 10 of the 12 population pairs; this contrasts with previously reported stochastic genetic divergence between these populations at random markers. Our results indicate that behavioural traits related to harm avoidance and associated with the SERT polymorphism experience selection pressures during most blackbird urbanization events. These events thus appear to be influenced by homogeneous adaptive processes in addition to previously reported demographic founder events.原本为乡村物种的类群成功定居城市生境，为研究生物对新生境的适应性演化提供了理想的研究场景。本研究针对这一科学问题，选取被推测在这类定居过程中发挥作用的行为性状相关候选基因开展分析。我们以西古北界范围内12组配对的城市和乡村乌鸫（Turdus merula）种群为研究对象，对昼夜节律、避害行为以及迁徙与探索行为相关候选基因中的16个多态位点进行了鉴定与基因分型。作为避害行为候选基因的血清素转运体（SERT）基因中，存在一个外显子微卫星位点，在针对所有种群的联合分析中，该位点与生境类型呈现极显著的统计学关联。该位点在12组种群对中的10组里均表现出一致的遗传分化模式，这与此前报道的这些种群间随机分子标记的随机遗传分化特征形成鲜明反差。我们的研究结果表明，在多数乌鸫的城市定居过程中，与避害行为相关且与SERT基因多态性关联的行为性状正经受选择压力的作用。因此，除此前报道的奠基者种群人口统计学效应外，这类城市定居事件似乎还受到同质化适应性演化过程的影响。