Climate change allows species to expand polewards, but non-changing environmental features may limit expansions. Daylength is unaffected by climate and drives life cycle timing in many animals and plants. Because daylength varies over latitudes, poleward-expanding populations must adapt to new daylength conditions. We studied local adaptation to daylength in the butterfly Lasiommata megera, which is expanding northwards along several routes in Europe. Using common garden laboratory experiments with controlled daylengths, we compared diapause induction between populations from the southern-Swedish core range and recently established marginal populations from two independent expansion fronts in Sweden. Caterpillars from the northern populations entered diapause in clearly longer daylengths than those from southern populations, with the exception of caterpillars from one geographically isolated population. The northern populations have repeatedly and rapidly adapted to their local daylengths, indicating that the common use of daylength as seasonal cue need not strongly limit climate-induced insect range expansions.

中文翻译：

---

在两个平行的、气候引起的蝴蝶范围扩张的前沿局部适应季节性线索

气候变化允许物种向极地扩张，但不变的环境特征可能会限制扩张。昼长不受气候影响，并推动了许多动植物的生命周期时间。由于日长随纬度而变化，向极地扩张的种群必须适应新的日长条件。我们研究了蝴蝶Lasiommata megera对昼长的局部适应，它正在沿着欧洲的几条路线向北扩展。使用具有受控日长的普通花园实验室实验，我们比较了来自瑞典南部核心范围的种群与最近在瑞典两个独立扩张前沿建立的边缘种群之间的滞育诱导。来自北方种群的毛虫进入滞育期的时间明显比来自南方种群的更长，但来自一个地理上孤立种群的毛虫除外。北方种群已经反复快速地适应了当地的日长，这表明将日长作为季节性线索的普遍使用不需要强烈限制气候引起的昆虫活动范围的扩大。