Reduced size in a montane butterfly at its warm range boundaries: museum and contemporary Mountain ringlet wing size measurements

Variation in insect size is often related to temperature during
development, and may affect the persistence of populations under future
climate warming if smaller individuals have reduced fitness. Montane
species are particularly vulnerable to climate-driven local extinctions
due to range retractions at their warm range margins, and so we examined
spatial and temporal variation in body size in the
butterfly Erebia epiphron in the UK, where it is restricted to
two montane regions in England and Scotland. We examine spatial and
temporal variation in body size in relation to temperature. We sampled 19
populations (6-15 individuals per population) in England and Scotland
between 2018 and 2019 spanning elevations from 380-720 m, and examined
museum specimens collected between 1890 and 1980. We examined individual
body size (forewing length) and its relationship with the local
temperature of sites, as well as temporal variation in body size over the
last century in relation to the temperature during larval development. The
forewing lengths of field-collected individuals in England were on average
7-8% smaller than in Scotland (England, mean = 14.9 mm, Scotland, mean =
15.9 mm), and warmer sites also had smaller individuals (0.13mm reduction
in wing length per 1oC increase in local site mean temperature). However,
we found no effect of temporal temperature variation on body size changes
during larval development. E. epiphron were smaller in England than
Scotland, and at warm range edge populations, which could have impacts on
fecundity and dispersal ability. Future work should seek to understand the
life-cycle lengths, genetics and phenotypic plasticity of these two
populations to evaluate potential explanations for regional differences.

昆虫体型的变异通常与发育阶段的温度密切相关，若体型更小的个体适合度（fitness）降低，则可能影响未来气候变暖背景下种群的存续能力。
山地物种因其分布暖缘的范围收缩，尤其易受气候驱动的局域灭绝威胁，因此我们针对英国境内仅分布于英格兰与苏格兰两个山地区域的蝴蝶埃瑞眼蝶（Erebia epiphron），探究了其体型的空间与时间变异及其与温度的关联。
2018至2019年间，我们在英格兰与苏格兰海拔380至720米的范围内采样了19个种群（每个种群含6至15只个体），同时检视了1890至1980年间采集的馆藏标本。
我们测定了个体的前翅长度，分析了其与样点本地温度的相关性，以及近一个世纪以来体型的时间变异与幼虫发育阶段温度的关联。
英格兰野外采集个体的前翅长度平均较苏格兰个体小7%至8%（英格兰种群平均为14.9毫米，苏格兰种群平均为15.9毫米）；样点本地温度越高，个体体型越小——本地年平均温度每升高1℃，翅长缩短0.13毫米。
但我们未发现幼虫发育阶段的温度时间变异对体型变化存在显著影响。
埃瑞眼蝶在英格兰的种群体型较苏格兰更小，且分布于暖缘的种群个体体型亦偏小，这可能对其繁殖力与扩散能力造成负面影响。
未来研究应聚焦于这两个种群的生活史周期、遗传机制与表型可塑性（phenotypic plasticity），以解析区域体型差异的潜在成因。