Electronic Supplementary Material for
Warmer Ambient Temperature Depress Liver Function in a Mammalian Herbivore
authored by Patrice Kurnath and M. Denise Dearing
MATERIAL AND METHODS
Temperature Treatments
Mojave Desert temperature data were obtained from a meteorological station maintained
by NOAA and the Western Regional Climate Center at Lytle Ranch, UT (37°09’N, 114°01’W)
for the past 30 years (www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?ut5252). The mean monthly
temperatures here for May-September included the temperature treatments from the present
study (20-29°C) and there was a consistent 10°C difference between mean maximum and
minimum values. A second weather station in St. George, UT (37°12’N, 113°57’W) maintained
by the USGS from 1928-1996 (http://mojave.usgs.gov/climate-history/index.html) was also
referenced for additional daily maximum and minimum temperature values.
Temperature treatments were not chosen to reflect the estimated changes in average
surface temperature due to climate change. Rather, treatments were selected to represent
temperatures within the thermal neutral zone (TNZ, 29°C) and just below the TNZ (21°C) for N.
Figure S1. Relationship between metabolic rate and ambient temperature
of three desert woodrats (Neotoma lepida). The thermal neutral zone
extends from approximately 25-35°C, as indicated by the flat black line.
Line made with lowess smoothing function in R (www.r-project.org).
lepida (figure S1). Metabolic rates increase when ambient temperatures are outside the TNZ as
mammals must expend energy to maintain thermal homeostasis. Based on studies with Neotoma
and laboratory rodents, we predicted that mammalian herbivores will be able to handle the
highest dose of toxins at temperatures slightly lower than the lower critical temperature of the
TNZ [2, references therein].
Differences between the metabolic rates of N. lepida at 21°C and 29°C are unlikely to
explain the differences observed in our liver function assay. If metabolic rates governed liver
function, then the highest capacity for detoxification should be observed at extremely low
ambient temperatures where metabolic rates are also highest. However, data from laboratory
rodents does not support this prediction; animals had reduced toxin tolerance at ambient
temperatures outside the TNZ (8°C) where metabolic rates are highest [3]. Data from our
preliminary studies on metabolic rates and clearance times of woodrats did not reveal a
correlation between these two variables (figure S2).
Figure S2. Preliminary relationship between metabolic rates and
clearance times after a long, 30-day acclimation period at two ambient
temperatures (blue = 21°C, red = 29°C) in Neotoma lepida. Each point
represents a single individual. Clearance times are indicative of liver
function; longer times equate to reduced liver function.
Table S1. Ambient temperature (mean + 1 s.e.) of animal rooms (cool or warm) after two acclimation
periods.
maximum (°C)
minimum (°C)
long, 30-day acclimation
short, 3.5-hour exposure
cool
warm
cool
warm
22.8 + 0.2
21.1 + 0.2
29.4 + 0.2
27.8 + 0.2
20.6 + 0.9
20.0 + 0.5
28.9 + 0.2
28.3 + 0.3
Measuring Metabolic Rates
The procedure was followed as per [14]. Woodrats in the TNZ study were housed at
room temperature (23-25°C) for at least one month and the chamber temperature ranged from
16-36°C during data collection. Woodrats used for metabolic rate and liver clearance time
comparisons were housed at either 21°C or 29°C for at least three weeks and the chamber
temperature was maintained at either 21°C or 29°C, matching the acclimation temperature of the
animal.
REFERENCES
2.
Dearing M.D. 2013 Temperature-dependent toxicity in mammals with implications for
herbivores: a review. Journal of Comparative Physiology B 183(1), 43-50.
(doi:10.1007/s00360-012-0670-y).
3.
Keplinger M.L., Lanier G.E., Deichmann W.B. 1959 Effects of environmental temperature
on the acute toxicity of a number of compounds in rats. Toxicology 1(2), 156-161.
14.
McLister J., Sorensen J., Dearing M. 2004 Effects of consumption of juniper (Juniperus
monosperma) on cost of thermoregulation in the woodrats Neotoma albigula and Neotoma
stephensi at different acclimation temperatures. Physiological and biochemical zoology :
PBZ 77(2), 305-312. (doi:10.1086/380211).