Cities represent a unique ecosystem dominated by humans and highdensity man-made infrastructure, associated with modifications or entire loss of local habitats. Thus, urbanization constitutes a considerable challenge for wildlife, and only a minority of species is able to persist in cities (Niemelä et al. 2011). Species that maintain populations in cities are usually characterized by significant changes in life history characteristics, population structure, and ecological relations (Niemelä et al. 2011). So far, most studies in urban ecology of vertebrates have focused on birds and mammals, whereas city-dwelling ectotherms, including reptiles, remain understudied (Niemelä et al. 2011; Hudson and Virgin 2018). However, considering that the worldwide decline of reptiles is largely associated with habitat deterioration (Gibbons et al. 2000) it is critical and urgent to assess the responses of reptilian populations toward an urbanized environment. Here, we investigated the impact of the urban environment on body size, as the primary fitness-relevant trait, in a widespread Eurasian reptile, the grass snake Natrix natrix, by comparing 2 replicate urban populations with suband non-urban sites. Due to the documented reduction of prey availability (amphibians) in cities including the studied metropolitan area (Budzik et al. 2013), we predict that urban grass snakes will tend to exhibit smaller body size compared with suband non-urban sites, similary to previous studies on snakes (Wolfe et al. 2018). In addition, a high density of roads and higher incidence of deliberate killing in cities may increase mortality mainly of larger specimens (Andrews and Gibbons 2008, Niemelä et al. 2011). Because grass snakes express clear sexual size dimorphism (SSD) with females larger than males (Madsen and Shine 1993), we expect that the anticipated mortality will result in a skewed sex ratio with underrepresentation of females in urban sites. The study was conducted on 4 populations of the grass snake in southern Poland in Kraków and its vicinity. Kraków is the capital of Lesser Poland Voivodeship and is one of the largest Polish cities with a human population size exceeding 750,000 and well-developed urban infrastructure. We identified 2 urban sites with remaining patches of natural habitat occupied by the grass snake situated close to the city center and surrounded entirely (site Urban I) or in ca. 70% (site Urban II) by buildings and roads. The third population (site Suburban) was located in the suburbs within the administrative boundaries of Kraków in a riparian woodland along the Vistula River surrounded by allotments but not city buildings. The 4th population was located outside of Kraków (site Non-urban) entirely in a large patch of lowland forest of Puszcza Niepołomicka. Sub-adult to adult (>30 cm SVL) snakes were captured throughout the active season (April–October) in each population in parallel. For each snake, we assessed snout–vent length (SVL) and sex by examining tail morphology and probing when necessary. Snakes were marked individually with scale clipping. Overall, we collected data on 13 males and 18 females in site Urban I, 11 males and 11 females in site Urban II, 21 males and 17 females in site Sub-Urban, 10 males and 14 females in site Non-Urban. A 2-way ANOVA revealed that SVL is significantly affected by the interaction of population and sex (F3,107 1⁄4 7.71; P<0.001; Supplementary Table S1; Figure 1). A post hoc Tukey test showed that significant differences occurred between sexes in both Suband Non-Urban sites (Supplementary Table S2; Figure 1), whereas no differences were detected in snakes from both urban sites (Urban I and Urban II) (Supplementary Table S2; Figure 1). Male body size did not differ between populations, whereas females were larger in Sub-urban and Non-urban sites compared with both urban (Urban I and Urban II) populations (Supplementary Table S2; Figure 1). Sex ratio did not deviate from 1:1 in Urban I (chi 1⁄4 0.81; P1⁄40.37), Urban II (chi1⁄40.0; P1⁄41), Sub-urban (chi 1⁄4 0.42; P1⁄40.52), or Non-urban (chi 1⁄4 0.66; P1⁄40.41) populations. Descriptive statistics are provided in Supplementary Table S3. Our study represents the first report of decrease in size of 1 of sexes leading to loss of sexual size dimorphism in native species imposed by the urban environment (Hudson and Virgin 2018). As

中文翻译：

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一种广泛分布的爬行动物欧洲草蛇 Natrix natrix 在城市种群中性别大小二态性的丧失

城市代表了一个由人类和高密度人造基础设施主导的独特生态系统，与当地栖息地的改变或完全丧失有关。因此，城市化对野生动物构成了相当大的挑战，只有少数物种能够在城市中生存（Niemelä et al. 2011）。在城市中维持种群的物种通常以生活史特征、种群结构和生态关系发生显着变化为特征（Niemelä 等，2011）。到目前为止，脊椎动物城市生态学的大多数研究都集中在鸟类和哺乳动物上，而居住在城市的外温动物，包括爬行动物，仍未得到充分研究（Niemelä et al. 2011; Hudson and Virgin 2018）。然而，考虑到爬行动物在世界范围内的减少在很大程度上与栖息地恶化有关（Gibbons 等人，2000）评估爬行动物种群对城市化环境的反应至关重要且紧迫。在这里，我们通过比较 2 个城市人口与郊区和非城市地点的重复城市种群，研究了城市环境对体型的影响，作为主要与健康相关的特征，在广泛分布的欧亚爬行动物草蛇 Natrix natrix 中。由于包括研究的大都市区在内的城市中猎物（两栖动物）的记录减少（Budzik 等人，2013 年），我们预测城市草蛇与郊区和非城市地点相比将倾向于表现出更小的体型，类似于以前的对蛇的研究（Wolfe 等人，2018 年）。此外，城市中高密度的道路和更高的蓄意杀戮发生率可能会增加主要较大标本的死亡率（Andrews and Gibbons 2008，Niemelä 等 2011）。因为草蛇表现出明显的性别大小二态性 (SSD)，雌性大于雄性（Madsen 和 Shine 1993），我们预计预期的死亡率将导致性别比例偏斜，城市中雌性的代表性不足。该研究是在波兰南部克拉科夫及其附近地区的 4 个草蛇种群中进行的。克拉科夫是小波兰省的首府，是波兰最大的城市之一，人口超过 75 万，城市基础设施发达。我们确定了 2 个城市遗址，其中剩余的自然栖息地被草蛇占据，靠近市中心并被完全包围（城市 I 遗址）或大约在 70%（Urban II 场地）由建筑物和道路组成。第三个人口（站点郊区）位于克拉科夫行政边界内的郊区，位于维斯瓦河沿岸的河岸林地中，周围环绕着土地，但没有城市建筑。第 4 人口位于克拉科夫（非城市站点）之外，完全位于 Puszcza Niepołomicka 的一大片低地森林中。在每个种群的活跃季节（4 月至 10 月）中，从亚成年到成年（> 30 厘米 SVL）的蛇被同时捕获。对于每条蛇，我们通过检查尾巴形态和必要时进行探查来评估口鼻部长度 (SVL) 和性别。蛇用鳞片剪裁单独标记。总体而言，我们收集了城市 I 站点的 13 名男性和 18 名女性、城市 II 站点的 11 名男性和 11 名女性、Sub-Urban 站点的 21 名男性和 17 名女性、非城市站点的 10 名男性和 14 名女性的数据。2 项方差分析显示 SVL 受人口和性别相互作用的显着影响（F3,107 1⁄4 7.71；P<0.001；补充表 S1；图 1）。事后 Tukey 检验表明，在郊区和非城市站点（补充表 S2；图 1）的性别之间存在显着差异，而在来自两个城市站点（城市 I 和城市 II）的蛇中未检测到差异（补充表 S2） ; 图1）。男性的体型在人群之间没有差异，而与城市（城市 I 和城市 II）人口相比，郊区和非城市地区的女性更大（补充表 S2；图 1）。城市I（chi 1⁄4 0.81；P1⁄40.37）、城市II（chi1⁄40.0；P1⁄41）、郊区（chi 1⁄4 0.42；P1⁄40.52）的性别比未偏离1:1 , 或非城市 (chi 1⁄4 0.66; P1⁄40.41) 人口。补充表 S3 中提供了描述性统计数据。我们的研究代表了第一份关于城市环境强加的本地物种性别大小二态性减少导致性别大小二态性丧失的报告（Hudson and Virgin 2018）。作为