DOI: 10.5061/dryad.ttdz08m61
title: Reduced size in a montane butterfly at its warm range boundaries: museum and contemporary Mountain ringlet wing size measurements

description: 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.
description: In 2018 and 2019, we collected 6-15 male <em>E. epiphron
 </em>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 (5-7.6<sup>o</sup>C 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 measured and averaged. A measurement accuracy of ±0.3mm was estimated based on three replicate measurements of 10 random individuals.
description: # 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 averaged between the two forewings Region: either Lakes Lake District population or Scotland Population: Subpopulation where collected and corresponding 1km Grid Reference **NHM_all** all data are measured from photos from [https://data.nhm.ac.uk/](https://data.nhm.ac.uk/) This file includes all raw measures of museum 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 averaged between the two forewings Locality: Nearest named location from museum label (NA represent where no locality information was present on museum label, beyond England/Scotland - see region) year: year of collection from museum label Region: Either England (Lake District) or Scotland