DOI: 10.5061/dryad.2280gb64w
title: Exploring reversibility and contrasting patterns in temperature-size relationships across spatial and temporal scales using subfossil chironomids

description: The extent to which different magnitudes and directions of temperature
 fluctuations explain long-term trends in aquatic invertebrate body size in
 nature is largely unknown. Using elevation gradients and paleolimnological
 reconstructions, we tested the hypotheses that variations in subfossil
 chironomid (non-biting midges) head capsules (HC) will covary with
 temperature changes, with opposite morphometric changes occurring during
 warming and cooling phases, and that body size variation can be modified
 by other environmental conditions unassociated with temperature
 variations. Results indicated that the effects of increasing temperatures
 on chironomid HC size were reversed when temperatures decreased, with both
 warming and cooling producing similar effect sizes, corresponding to a
 change in HC length of ~3% per 1°C. Additionally, our results showed that
 other environmental drivers can mask temperature effects on chironomid HC
 sizes. Specifically, we found that bottom water oxygen concentration was
 negatively associated with HC lengths of Chironomus anthracinus-type. We
 hypothesize that this pattern is driven by prolonged larval development in
 oxygen-depleted lakes and/or changes in basal food sources used by
 chironomid larvae, ultimately affecting their final body size. To gain a
 better understanding of aquatic insect size variation over long
 timescales, it is essential to uncover the underlying mechanisms that
 control their body size, as these factors may either enhance or compound
 the temperature-size relationship.
description: # Exploring reversibility and contrasting patterns in temperature-size
 relationships across spatial and temporal scales using subfossil
 chironomids Dataset DOI:
 [10.5061/dryad.2280gb64w](10.5061/dryad.2280gb64w) ## **Description of the
 data and file structure** This dataset contains information on head
 capsule lengths and associated lake characteristics across different
 climatic contexts. The measurements comprised quantification of the length
 between the top of the median tooth of the mentum (for *Micropsectra
 insignilobus*-type and *Chironomus anthracinus*-type) or the center of the
 median teeth (for *Sergentia coracina*-type), and the base of the HC (for
 *Sergentia coracina*-type and *Chironomus anthracinus*-type) or the inner
 margin of the post-occipital plate (for *Micropsectra insignilobus*-type).
   ·       Files with “elevation” in the filename include data on lake
 characteristics (e.g., elevation, coordinates, water chemistry) as well as
 the average head capsule (HC) lengths for different morphotypes found
 across various lakes. ·       File with “HC_downcore” in the filename
 presents HC length measurements for different morphotypes found in various
 sediment core samples. These measurements are organized by lake and
 period, corresponding to distinct climatic periods. All measurements were
 collected and analyzed following standardized procedures (Belle 2025;
 [https://doi.org/10.1007/s10933-025-00366-y](https://doi.org/10.1007/s10933-025-00366-y)) to ensure comparability across samples and periods. For detailed metadata, abbreviations, and sampling protocols, please refer to the accompanying paper or contact the corresponding author. **Files and variables** **File: C_anthracinus_elevation.txt** **Description:** HC lengths of *Chironomus anthracinus*-type from six lakes **Variables** * Lake: ALA= Älgarydssjön; LIL= Lilla Öresjön; OVR = Örvattnet; LAG= Lagmanshagsjön; BYS= Bysjön; TAF= Täftesträsket. * HC_length: µm * Lake_bottom_O2: oxygen concentration expressed in mg/L * Elevation: m a.s.l. * Latitude: oN * MJAT: Mean July Air Temperature; oC * Lake_Size: km2 * Lake_Depth: maximum water depth in meters * Secchi: Secchi depth in meters * Conductivity: water conductivity expressed in µS/cm * TOC: total organic carbon concentration expressed in mg/L * TN: total nitrogen concentration expressed in µg/L * TP: total phosphorus concentration expressed in µg/L * Ca: Calcium concentration expressed in mg/L **File: M_insignilobus_elevation.txt** **Description:** HC lengths of *Micropsectra insignilobus*-type from eight lakes across the current-day spatial gradient **Variables** * Lake: FOR = Forsjön; SKA = Skärlen; TOR = Torrgårdsvatten; VBA = Västra Bavlanjaevrieh; s1066 = Sjö 1066 ; Alp1 = Alpine 1; Alp3 = Alpine 3; Dikt = Diktar Erik. * HC_length: µm * Elevation: m a.s.l. * Latitude: oN * MJAT: Mean July Air Temperature; oC * Lake_Size: km2 * Lake_Depth: maximum water depth in meters * Secchi: Secchi depth in meters * Conductivity: water conductivity expressed in µS/cm * TOC: total organic carbon concentration expressed in mg/L * TN: total nitrogen concentration expressed in µg/L * TP: total phosphorus concentration expressed in µg/L * Ca: Calcium concentration expressed in mg/L **File: S_coracina_elevation.txt** **Description:** HC lengths of *Sergentia coracina*-type from eight lakes across the current-day spatial gradient **Variables** * Lake: Alp3 =Alpine 3; Alp1 = Alpine 1; STBJ = Stor-Bjösjön; VSK = Västra Skälsjön; FOR = Forsjön; OSK = Östra Skälsjön; BYS = Bysjön; OVR = Örvattnet. * HC_length: µm * Elevation: m a.s.l. * Latitude: oN * MJAT: Mean July Air Temperature; oC * Lake_Size: km2 * Lake_Depth: maximum water depth in meters * Secchi: Secchi depth in meters * Conductivity: water conductivity expressed in µS/cm * TOC: total organic carbon concentration expressed in mg/L * TN: total nitrogen concentration expressed in µg/L * TP: total phosphorus concentration expressed in µg/L * Ca: Calcium concentration expressed in mg/L **File: HC_length_downcore.txt** **Description:** Temporal response of HC lengths of *Chironomus anthracinus*-type, *Micropsectra insignilobus*-type, and *Sergentia coracina*-type to the different climate phases. **Variables** * Lake: Alp3 = Alpine 3; Araisi; Diktar = Diktar Erik; Alp1 = Alpine 1; Jar = Järveotsa; VSK = Västra Skälsjön; BYS = Bysjön. * Periods: BA = *ca*. 13,500 cal. BP; YD = *ca*. 12,000 cal. BP; EH = *ca*. 10,000 cal. BP; HTM = *ca*. 5000 cal. BP; LIA = at *ca*. 1900 AD; present = *ca*. 1920 – 2017 AD for Alp1 and Alp3, and *ca*. AD 1990 – 2020 AD for BYS and VSK. * Trend: “cooling” indicates cooling trends, while “warming” denotes warming phases. * Taxa: MI: Micropsectra insignilobus-type; SC: Sergentia coracina-type; CA: Chironomus anthracinus-type * HC_length: µm