DOI: 10.5061/dryad.w6m905qx3
title: Data from: lactation at hot temperature: a test of heat dissipation limitation in mice divergently selected for BMR

description: The HDL (Heat Dissipation Limitation) hypothesis posits that mammalian
 energy budgets (SuSMR, Sustained Metabolic Rate) are limited by the
 ability to dissipate metabolic heat. The HDL hypothesis has often been
 tested in lactating mice but rarely in females, systematically differing
 in SuSMR. Here, we used lines of laboratory mice divergently selected for
 Basal Metabolic Rate (BMR) and effectively co-selected for SuSMR. We
 exposed lactating females to 23°C and 30°C and manipulated their heat
 dissipation abilities by fur shaving. Exposure to 30°C did not affect the
 high BMR mice' litter mass but increased litter mass in the low BMR
 mice. Fur shaving did not affect litter mass. However, it decreased body
 temperature (Tb) by 0.2°C in the shaved mice, independent of line
 affiliation and ambient temperature. In both lines exposed to 30°C, the Tb
 increased by 0.2°C, while Daily Energy Expenditures (DEEs - a proxy of
 SuSMR) decreased by 20% and still was higher in the high BMR mice. These
 results do not support the HDL hypothesis. Low SuSMR individuals may
 benefit from higher ambient temperatures because of reduced costs of
 thermoregulation. It may change the course of natural selection towards
 reducing SuSMR and BMR.
description: Dataset was collected in January 2018 for the
 53<sup>rd</sup> generation of laboratory mice (<em>Mus
 musculus</em>) artificially selected towards either high and low
 basal metabolic rate (respectively H-BMB and L-BMR lines; details in
 Książek et al. 2004) at the Faculty of Biology of the University of
 Bialystok. We conducted one experiment, assessing the response of
 lactating mice to exposure to an ambient temperature of 23°C and 30°C and
 fur shaving as a heat dissipation manipulation procedure. Before the
 proper experiment, 25 randomly chosen females from both line types were
 implanted intraperitoneally with loggers (type DST nano-T, size 6 mm x 17
 mm, weight 1.3 g, Star Oddi Logging Life Science, Iceland) to control body
 temperature (T<sub>b</sub>) every 10 minutes throughout
 lactation (± 0.01°C; records between 9.00 and 10.30 a.m. were deleted from
 analyses because of disturbances caused by human activity). Prior to the
 implantation of the loggers, females were anesthetized with xylazine (40
 mg of xylazine per kilogram of body mass) and ketamine (100 mg of ketamine
 per kilogram of body mass). Before the pregnancy, we controlled
 females' body mass and body temperature. Then, females raised at 23°C
 were mated with non-sibling males from the same line type, and when
 pregnancy was detected by the increase in body mass, males were removed
 from the cages. The experiment began on the parturition day when mother
 mice with their natural litters were randomly exposed to an ambient
 temperature of 23°C or 30°C. On the 6<sup>th</sup> and
 10<sup>th</sup> days of lactation, mother mice from both line
 types, lactating at both ambient temperatures, were dorsally shaved with
 an electric clipper (Remington). On the 12<sup>th</sup> day of
 lactation we controlled litter mass (as a proxy of parental effort),
 litter size (number of pups per litter) and female body mass. Between the
 12<sup>th</sup> and 14<sup>th </sup>day of
 lactation, we assessed daily energy expenditures (DEEs), metabolizable
 energy intake (MEI) and milk energy output (MEO) by doubly labelled water
 method (DLW). Analyses were carried out by Doubly-Labelled Water
 Laboratory at the University of Aberdeen. The experiment was terminated on
 the 14<sup>th</sup> day of lactation. We used 57 females of
 laboratory mice (originating from a separate family): 30 from the L-BMR
 line type (6 with fur and 6 shaved at 23°C and 8 with fur and 10 shaved at
 30°C) and 27 from the H-BMR line type (7 with fur and 7 shaved at 23°C and
 6 with fur and 7 shaved at 30°C). Differences in litter
 mass, litter size, maternal T<sub>b</sub>, maternal body mass,
 DEEs, MEI and MEO at the peak of lactation were tested by three-way
 ANOVA/ANCOVA, in which a line type affiliation (L-BMR or H-BMR), an
 ambient temperature (23°C or 30°C) and manipulation (shaved or unshaved)
 were the main fixed effects. Litter mass on the 12<sup>th
 </sup>day of lactation was applied as a covariate in the case of
 T<sub>b</sub> and DEE analysis. Significance was tested at P =
 0.05. Statistical analyses were carried out using the STATISTICA version
 13.3 package.
description: # Lactation at hot temperature: a test of heat dissipation limitation in
 mice divergently selected for BMR
 [https://doi.org/10.5061/dryad.w6m905qx3](https://doi.org/10.5061/dryad.w6m905qx3) The database is associated with the paper and supplementary materials entitled: Lactation at hot temperature: a test of heat dissipation limitation in mice divergently selected for basal metabolic rate. It consists of one file named 'Lactation at hot temperature: a test of heat dissipation limitation in mice divergently selected for BMR'. We presented raw data collected during the experiment course. ## Description of the data and file structure Codebook for the data: **Sheet: data** * Obs – the ordinal number of the observation * female's ID – identification number of lactating mice * shaved – mice subjected to the procedure of fur shaving on the 6th and 10th day of lactation * unshaved – mice not subjected to the procedure of fur shaving on the 6th and 10th day of lactation * H-BMR - mice with experimentally confirmed affiliation to a line with a high rate of basal metabolism (H-BMR line type) * L-BMR - mice with experimentally confirmed affiliation to a line with a low rate of basal metabolism (H-BMR line type) * 23 – mice exposed to an ambient temperature of 23°C for the 14-day lactation period * 30 - mice exposed to an ambient temperature of 30°C for the 14-day lactation period * DEE – the value of dams' daily energy expenditures for the period between the 12th and 14th day of lactation (kJ/day-1) - MEI – the value of dams' metabolizable energy intake for the period between the 12th and 14th day of lactation (kJ/day-1) - MEO – the value of dams' milk energy output for the period between the 12th and 14th day of lactation (kJ/day-1) - female body mass before pregnancy (g) – the value of females’ body mass before getting pregnant (g) - female body mass on the 12th day of lactation (g) – the value of females’ body mass measured on the 12th day after parturition (g) - female body mass on the 14th day of lactation (g) – the value of females’ body mass measured on the 14th day after parturition (g) - carcass (g) – the value of females’ carcasses mass measured after dissection on the 14th day of lactation * litter mass on the 12th day of lactation (g) – the value of litter mass measured on the  12th day after parturition * pups number per litter on the 12th day of lactation – number of pups in each litter raised by dams measured on the 12h day after parturition * female body temperature before pregnancy (°C) – mean core body temperature measured on the day before getting pregnant (°C) * female body temperature on the 12th day of lactation  (°C) – mean core body temperature measured on the 12th day after parturition "." – measurement not taken **Sheet: experimental group** – file contains a list of females in the 8 experimental groups. * Females ID - identification number of lactating mice * Cage – number of mice family * Number – female's number in the litter