Data from: Urban versus forest ecotypes are not explained by divergent reproductive selection

Increasing urbanisation offers a unique opportunity to study adaptive responses to rapid environmental change. Numerous studies have demonstrated phenotypic divergence between urban and rural organisms. However, comparing the direction and magnitude of natural selection between these environments has rarely been attempted. Using seven years of nest-box breeding monitoring of great tits (Parus major) in the city of Montpellier and in a nearby oak forest, we find phenotypic divergence in four morphological and two life-history traits between urban and forest birds. We then measure reproductive selection on these traits, and compare selection between the habitats. Urban birds had significantly smaller morphological features than their rural counterparts, with shorter tarsus, lower body mass and smaller wing and tail lengths relative to their overall body size. While urban female tarsus length was under stabilising selection, and forest males show positive selection for tarsus length and negative selection for body mass, selection gradients were significantly divergent between habitats only for body mass. Urban great tits also had earlier laying dates and smaller clutches. Surprisingly, we found selection for earlier laying date in the forest but not in the city. Conversely, we detected no linear selection on clutch size in the forest, but positive selection on clutch size in the urban habitat. Overall, these results do not support the hypothesis that contemporary reproductive selection explains differences in morphology and life history between urban and forest breeding great tits. We discuss how further experimental approaches will help confirm whether the observed divergence is maladaptive while identifying the environmental drivers behind it.快速推进的城市化为研究生物对环境快速变化的适应性响应提供了独特契机。已有大量研究证实城市与乡村生物间存在表型分化（phenotypic divergence），但针对两类生境下自然选择（natural selection）的方向与强度开展对比的尝试却极少。本研究针对蒙彼利埃市及周边一片栎林中的大山雀（Parus major）开展了为期7年的巢箱繁殖监测，结果发现城市种群与森林种群在4项形态性状及2项生活史性状上均存在表型分化。随后我们对这些性状开展繁殖选择分析，并对比了两类生境下的选择模式差异。城市种群的形态特征整体显著小于乡村种群，相较于整体体型而言，城市大山雀的跗跖更短、体重更低，翅长与尾长也更小。尽管城市雌性大山雀的跗跖长度受到稳定选择（stabilising selection），森林雄性的跗跖长度则呈现正向选择、体重呈负向选择，但两类生境间选择梯度（selection gradients）存在显著差异的性状仅为体重。城市大山雀的产卵日期更早，窝卵数也更少。令人意外的是，森林种群中存在对更早产卵日期的选择，而城市种群中并无此类选择；与之相反，森林种群未检测到窝卵数的线性选择（linear selection），城市种群则对窝卵数存在正向选择。综合来看，本研究结果并不支持"当代繁殖选择能够解释城市与森林繁殖种群大山雀在形态及生活史性状上的差异"这一假说。我们还讨论了后续实验研究将如何帮助验证所观测到的表型分化是否属于适应不良（maladaptive），并厘清背后的环境驱动因子（environmental drivers）。