Populations undergoing rapid climate-driven range expansion experience distinct selection regimes dominated both by increased dispersal at the leading edges and steep environmental gradients. Characterisation of traits associated with such expansions provides insight into the selection pressures and evolutionary constraints that shape demographic and evolutionary responses. Here we investigate patterns in three components of wing morphology (size, shape, colour) often linked to dispersal ability and thermoregulation, along latitudinal gradients of range expansion in the Speckled Wood butterfly (Pararge aegeria) in Britain (two regions of expansion in England and Scotland). We measured 774 males from 54 sites spanning 799 km with a 10-year mean average temperature gradient of 4 °C. A geometric morphometric method was used to investigate variation in size and shape of forewings and hindwings; colour, pattern, and contrast of the wings were examined using a measure of lightness (inverse degree of melanism). Overall, wing size increased with latitude by ∼2% per 100 km, consistent with Bergmann’s rule. Forewings became more rounded and hindwings more elongated with history of colonisation, possibly reflecting selection for increased dispersal ability. Contrary to thermal melanism expectations, wing colour was lighter where larvae developed at cooler temperatures and unrelated to long-term temperature. Changes in wing spot pattern were also detected. High heterogeneity in variance among sites for all of the traits studied may reflect evolutionary time-lags and genetic drift due to colonisation of new habitats. Our study suggests that temperature-sensitive plastic responses for size and colour interact with selection for dispersal traits (wing size and shape). Whilst the plastic and evolutionary responses may in some cases act antagonistically, the rapid expansion of P. aegeria implies an overall reinforcing effect between these two mechanisms.

中文翻译：

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在范围扩大的蝴蝶中对纬度和定植的翅膀形态学反应

经历由气候驱动的快速范围扩张的种群经历了不同的选择制度，主要是前沿的扩散增加和陡峭的环境梯度。与这种扩展相关的特征的表征提供了对影响人口和进化反应的选择压力和进化约束的洞察。在这里，我们研究了翅膀形态的三个组成部分（大小、形状、颜色）的模式，通常与散布能力和体温调节有关，沿着英国的斑点木蝴蝶（Pararge aegeria）范围扩张的纬度梯度（英格兰和英国的两个扩张区域）。苏格兰）。我们测量了来自 799 公里 54 个地点的 774 名雄性，10 年平均温度梯度为 4 °C。几何形态测量方法用于研究前翅和后翅的大小和形状的变化；翅膀的颜色、图案和对比度使用亮度测量（黑色素的反程度）来检查。总体而言，机翼尺寸随纬度每 100 公里增加约 2%，与伯格曼规则一致。随着殖民历史的发展，前翅变得更圆，后翅变得更细长，这可能反映了对分散能力增强的选择。与热黑色素预期相反，幼虫在较冷的温度下发育并且与长期温度无关，翅膀颜色较浅。还检测到翼斑图案的变化。研究的所有性状的地点之间差异的高度异质性可能反映了由于新栖息地的殖民化导致的进化时间滞后和遗传漂移。我们的研究表明，对大小和颜色的温度敏感塑料响应与对分散性状（翅膀大小和形状）的选择相互作用。虽然可塑性和进化反应在某些情况下可能会产生对抗作用，但 P. aegeria 的快速扩张意味着这两种机制之间的整体增强作用。