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..., In 2018 and 2019, we collected 6-15 male E. epiphron from each of 9 populations in England and 10 populations in Scotland representing a wide range of local elevation (380-780 m above sea level) and temperature gradients (5-7.6oC mean annual temperature). Wings were removed from individuals and electronically scanned.
Photographs of specimens held at the Natural History Museum, London (2014) were downloaded (https://data.nhm.ac.uk/), and up to 5 males collected between 1890 and 1987 were measured (England n = 127 individuals, Scotland n = 100).
We measured forewing length (distance between cell base and v10 wing margin veins; see Supplementary Materials SM1), a widely accepted proxy for body size, using the ‘draw line’ tool in Image J (https://imagej.nih.gov/ij/index.html). The length in pixels was converted into millimetres using the scale bar. Only wings where all veins and cell bases were visible were used for measurements. For each individual, both left and right forewings were meas..., , # Mountain ringlet wing measurements

[https://doi.org/10.5061/dryad.ttdz08m61](https://doi.org/10.5061/dryad.ttdz08m61)

## Description of the data

This data set includes two spreadsheets of wing sizes for *Erebia epiphron* (forewing length/width and hindwing length/width) in field-caught contemporary material and museum specimens from the UK. \"Contemporary_all\" includes modern specimens caught from 19 populations in England and Scotland between 2018-2019, and \"NHM_all\" contains measures for museum specimens from England and Scotland between 1890 and 1987. Any NAs represent where measure was not possible, e.g. wing was missing or damaged. 

**Contemporary_all**

This file includes all raw measures of contemporary wing length including:

FW_length: length of forewing in mm averaged between the two forewings

FW_width: width of forewing in mm averaged between the two forewings

HW_length: length of hindwing in mm averaged between the two forewings

HW_width: width of hindwing in mm ave...