DOI: 10.5061/dryad.3tx95x6qp
title: Measures of cold tolerance in diploid and triploid Daphnia clones exposed to two temperatures

description: Despite decades of studies on the differential distribution of polyploid
 organisms, the causes of this pattern have yet to be elucidated. This
 study aimed to explore some of the possible physiological mechanisms
 explaining the differential northern distribution of polyploid clones of
 Daphnia pulex compared to the one of the diploid parental species. The
 critical thermal minimum (CTmin) was measured in 17 D. pulex clones of
 contrasted ploidy (diploid and triploid) and geographic origins (temperate
 and subarctic climates) reared under low and high temperatures (16 and 24
 °C). Triploid clones had better cold tolerance (lower CTmin) than both
 sympatric and temperate diploid clones. No significant association was
 found between CTmin and body size nor with cell size. We suggest that
 triploids might express a cold shock resistant phenotype related to higher
 gene expression and/or fatty acid profiles. Cold tolerance can be viewed
 as one of the possible reasons for polyploid preponderance in subarctic
 climates.
description: Several diploid and triploid clones of <em>Daphnia pulex
 </em>from temperate and subarctic North American regions were reared
 for at least three generations in standardized conditions before the
 experiments to eliminate potential maternal effects (6 subarctic triploid
 clones, 4 subarctic diploid clones, 8 temperate diploid clones). Cold
 tolerance was tested by performing a critical thermal minimum (CTmin)
 challenge. A total of 543 daphnids (268 acclimated at 16°C and 275 at 24
 °C respectively) from 18 clones were tested for cold tolerance. To find
 out which variables have a significant effect on cold tolerance, body size
 or cell area, linear mixed models were used (‘lme4’ (Bates<em>
 </em>et al<em>.</em> 2015) and ‘lmerTest’
 (Kuznetsova<em> </em>et al<em>.</em> 2017)
 packages). Our experimental design was hierarchical, with each clone being
 replicated in three jars at each temperature and several individuals were
 sampled <em>per</em>jar. Clones and jar were computed as
 random factors. The same random effect structure was used for all models.
 Cell area and body size were standardized (mean = 0, SD = 1) to allow for
 a better interpretation of parameter estimates (see Schielzeth (2010) for
 more details).
description: # Cold tolerance in Daphnia
 [https://doi.org/10.5061/dryad.3tx95x6qp](https://doi.org/10.5061/dryad.3tx95x6qp) ## Description of the data and file structure \# Polyploidy confers better cold tolerance in Daphnia Data for cold tolerance in Daphnia clones raised under two temperatures. Contact France Dufresne ([france_dufresne@uqar.ca](mailto:france_dufresne@uqar.ca)) with any questions. This manuscript has been accepted for publication (11/12/2024): Pecl I, Blier P. Dufresne F. Polyploidy confers better cold tolerance in Daphnia. Oikos (accepted).  Cold tolerance was tested by performing a critical thermal minimum (CTmin) challenge. A total of 543 daphnids (268 acclimated at 16°C and 275 at 24 °C respectively) from 18 clones were tested for cold tolerance.Body size and cell area measures were carried out right after CTmin test.To find out which variables have a significant effect on cold tolerance, body size or cell area, linear mixed models were used (‘lme4’ (Bates* *et al*.* 2015) and ‘lmerTest’ (Kuznetsova* *et al*.* 2017) packages). Our experimental design was hierarchical, with each clone being replicated in three jars at each temperature and several individuals were sampled *per *jar. Clones and jar were computed as random factors. The same random effect structure was used for all models. Cell area and body size were standardized (mean = 0, SD = 1) to allow for a better interpretation of parameter estimates (see Schielzeth (2010) for more details). The assumptions of homoscedasticity, independence and normality of residuals were validated graphically. All statistical analyses were performed using R 4.2.2 (R Core Team, 2022). The R script file is : CTmin.r ### Files and variables #### File: Data\_Ctmin.xlsx **Description:** File containing Ctmin measures on clones from two ploidy levels and acclimated to two temperatures ##### Variables Clone (category variable for genotypes tested), jar (category for the jar where the animals were held, three jars were set up per clone) ploidy (category variable, clones were either diploid or triploid), climate(category  variable,  temperate or subarctic), Tacc(acclimation temperature), Ctmin (quantitative variable, cold tolerance measurement), Tind (body size measures in mm), Tcell (cell size in um), Sex (categorical, either male or female), Tindlog10(log body size), Tcelllog10(log cell size).  Missing values are indicated with 'null'.  Code/software **CTmin.r** Rstudio linear mixed models were used (‘lme4’ (Bates* *et al*.* 2015) and ‘lmerTest’ (Kuznetsova* *et al*.* 2017) packages). All statistical analyses were performed using R 4.2.2 (R Core Team, 2022).