Effect of Temperature on Metabolic Rate of the Mud Turtle

ARTICLE IN PRESS

Journal of Thermal Biology 28 (2003) 595–600

Effect of temperature on metabolic rate of the mudturtle (Kinosternon subrubrum) Jacqueline D. Litzgusa,b, William A. Hopkinsa,*

a Savannah River Ecology Laboratory, University of Georgia, Drawer E, Aiken, SC 29802, USA b Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA

Received15 June 2003; accepted5 August 2003

Abstract

Temperature plays an important role in various aspects of the life history andphysiology of ectotherms. We examinedthe effect of temperature on standardmetabolicrate in the mudturtle, Kinosternon subrubrum. We measured O2 consumption andCO 2 production at 20 C and30 C using a flow through respirometery system. Standard metabolic rate was significantly higher at 30 C (9.25 ml O2/h, 6.35 ml CO2/h) comparedto 20 C (2.10 ml O2/h, 1.96 ml CO2/h). The Q10 value for O2 was 5.10, andfor CO 2 was 3.40. Our findings generally agree with those of other studies of metabolism in vertebrate ectotherms. Publishedby Elsevier Ltd.

Keywords: Carbon dioxide production; Kinosternon subrubrum; Oxygen consumption; Q10; RQ; Respiratory quotient; Standard metabolic rate; Temperature; Turtle

1. Introduction development of models that describe the energy budgets of organisms (Lillywhite, 1987; Secor andNagy, 1994 ; Temperature plays an important role in various Beaupre, 1995, 1996), which in turn strongly influence aspects of the life history, ecology, andphysiology of life histories (Congdon et al., 1982; Dunham et al., reptiles andother ectotherms ( Angilletta et al., 2002). 1989). Growth rates (ArnoldandPeterson, 1989 ; Avery, 1994; An examination of variation in individual metabolic Litzgus andBrooks, 1998a ), reproduction (Schwarzkopf response to environmental variation (i.e., temperature andShine, 1991 ; Litzgus andBrooks, 1998b ; Rock and changes) can elucidate mechanistic explanations for Cree, 2003), seasonal activity patterns andhabitat use broadecological andevolutionary patterns ( Congdon (Webb andShine, 1998 ; Whitaker andShine, 2002 ), and et al., 1982). In addition, information on physiological geographic distribution (Castonguay et al., 1999) are all adaptations can be gleaned from intraspecific and influencedby environmental temperatures. Physiological interspecific comparative analyses (Garlandand processes such as metabolic rate generally increase with Adolph, 1994; Zaidan, 2003). Only a handful of studies temperature (e.g., Gatten, 1974; Bennett andDawson, on turtles have directly tested the effect of temperature 1976; Beaupre et al., 1993; Karasov andAnderson,1998 ; on metabolic rate. Oxygen consumption rates increased McNab, 2002); however, a few reptile species are known with temperature in the slider turtle (Trachemys scripta), to have plateaus of temperature-independent metabo- box turtle (Terrapene ornata)(Gatten, 1974), African lism (Waldschmidt et al., 1987). Information on how tortoise (Kinixys spekii)(Hailey andLoveridge,1997 ), temperature affects metabolic rates is useful for the andin hatchling snapping turtles ( Chelydra serpentina) (Steyermark andSpotila, 2000 ). Only one of these *Corresponding author. Tel.: +1-803-952-7427; fax: +1- studies examined both O2 consumption andCO 2 803-725-3309. production (Steyermark andSpotila, 2000 ). The purpose E-mail address: [email protected] (W.A. Hopkins). of this paper was to examine the effect of temperature on

0306-4565/$ - see front matter Publishedby Elsevier Ltd. doi:10.1016/j.jtherbio.2003.08.005 ARTICLE IN PRESS 596 J.D. Litzgus, W.A. Hopkins / Journal of Thermal Biology 28 (2003) 595–600

O2 consumption andCO 2 production rates of mud measurements were correctedfor standardtemperature turtles (Kinosternon subrubrum), andto compare our andpressure by the Oxymax ER-10 software. Turtles calculated Q10 andrespiratory quotient (RQ, the ratio of were weighed( 71 g) at the endof the experiment, and CO2 produced to O2 consumed) values to those reported returnedto their tote bins until release at their sites of for other reptile species. capture. From the VO2 andVCO 2 data collected, we estimated standard metabolic rate (SMR), the metabolic rate of a 2. Materials and methods post-absorptive animal at rest at a given temperature during the inactive part if its diel cycle (Bennett and Mudturtles are relatively small freshwater turtles, Dawson, 1976; Waldschmidt et al., 1987). Mudturtles, typically less than 12 cm in shell length (Ernst et al., like most vertebrate ectotherms, exhibitedspontaneous 1994). The species ranges from Long Island, New York, activity during respirometery trials (Fig. 1). In an effort southwardthrough Floridato the Gulf Coast, to exclude periods of activity from our estimates, westwardto central Texas, andnorthwardinto the SMR for VO2 andVCO 2 were determined by Mississippi Valley (Ernst et al., 1994). Mud calculating the mean of the lowest approximate 30% turtles (3 females, 4 males, mass range 97–220 g) of the data (4 of 13 data points) for each gas for each were collectedby handbetween 15 and25 February turtle. This methodof estimation eliminatedobvious 2003, shortly after emergence from hibernation, bouts of spontaneous activity (Fig. 1) andtherefore from the Francis Beidler Forest National Audubon appears to accurately represent SMR in our sample of andNature Conservancy Sanctuary near Harleyville, mudturtles. SC (33N, 80W). Beidler Forest is a 12,000-acre We calculatedthe respiratory quotient (RQ) for each nature preserve locatedin Four Holes Swamp, temperature treatment, andthe Q10s (20–30 C) for VO2 and includes cypress-tupelo blackwater swamp, hard- andVCO 2 using the SMR values. RQ (the ratio of CO2 woodbottom swamp, anduplandpine forest. Turtles produced to O2 consumed) allows inference about were brought into the lab where they were housedin aerobic catabolism (Withers, 1992). The effect of plastic tote bins (17 liters, 42 cm Â 30 cm Â 15 cm) temperature on metabolic processes can be described with shallow water, andfastedfor a minimum of 9 using the term Q10, which is defined as the change in the days to ensure post-absorptivity prior to metabolic rate of metabolism over a 10C change in temperature; determinations. Q10 normally has a value between 2 and3 ( McNab, Oxygen consumption (VO2) and carbon dioxide 2002). production (VCO2) were measuredusing a portable, To examine the effects of temperature on SMR, we flow-through respirometer (Oxymax ER-10, Columbus useda repeatedmeasures ANCOVA with bodymass as Instruments, Columbus, OH) interfacedto a laptop the covariate (proc mixedmodel,SAS Institute, Cary, computer. Each turtle was placedin a circular NC). To satisfy the assumption of linearity, both body Plexiglass chamber (volume B800 ml, diameter=15 cm, mass andSMR were log 10 transformedprior to height=5 cm) linedwith moist paper towels. Turtles statistical analyses. Statistical significance was accepted were not restrainedandcouldtherefore move freely at Po0.05. inside the chamber. Chamber volumes and leaks were measuredandcheckedby the Oxymax ER-10 software. Each chamber was attached to an independent 3. Results channel of the respirometer by tubing. The respirometer andchambers containing turtles were placedin an The effect of sex on SMR was not significant for incubator (Percival Scientific, Boone, Iowa; 24 h dark) either VO2 (F1,4=1.49, P=0.29) or VCO2 (F1,4=4.67, andmetabolic rate was measuredfor 24 h at each P=0.10); therefore, data for the sexes were pooled in all of two temperatures sequentially, 30C and20 C. further analyses. Similarly, the effect of mass on SMR Turtles were acclimatedto the treatment temperature was not significant for VO2 (F1,5=2.04, P=0.21) or while in respirometery chambers for 2 h prior to VCO2 (F1,5=4.42, P=0.09), although a positive linear commencement of metabolic rate determinations. Every trend was detected. Mean (7SE) SMR andRQs for 1.75 h, samples of air from each turtle chamber were each temperature treatment are shown in Table 1. passedover magnesium perchlorate andrates of VO 2 Temperature hada significant effect on SMR for both andVCO 2 were simultaneously determined by the VO2 (F1,6=26.94, Po0.01) andVCO 2 (F1,6=37.74, respirometer. The O2 andCO 2 sensors were purged Po0.001), such that as temperature increased, meta- with outside air passed over a column containing bolic rate increased. Spontaneous activity bouts were Drierite after each measurement. Thus, at both tem- also more frequent at the higher temperature (Fig. 1). peratures, a total of 13 measurements of each gas were Mean (7SE) Q10 (20–30 C) for VO2 was 5.1071.18, obtainedfor each turtle over the 24-h period.All andfor VCO 2 was 3.4070.52. ARTICLE IN PRESS J.D. Litzgus, W.A. Hopkins / Journal of Thermal Biology 28 (2003) 595–600 597

Fig. 1. Oxygen consumption (VO2, diamonds, A and B) and carbon dioxide production (VCO2, squares, C andD) of a mudturtle (Kinosternon subrubrum) (mass=220 g) at 20C (A andC) comparedto the same turtle at 30 C (B andD). The horizontal lines represent the standard metabolic rates (SMR) calculated as the mean of the lowest 30% of the data for each gas. The lowest 30% of the data are shown as solid symbols, and the highest 70% of the data (not used in the calculation of SMR) are represented as hollow symbols. This methodof estimation reducesthe inﬂuence of spontaneous activity on the calculation of SMR.

Table 1 metabolic rates of turtles did not test the effect of Mean7SE standard metabolic rate (SMR) measured indirectly temperature, making broadcomparisons of SMR values as oxygen consumption (VO2) and carbon dioxide production at various temperatures difficult. (VCO2), andrespiratory quotients (RQ) of mudturtles, In our mudturtles, the Q value (20–30C) for VO 7 7 10 2 Kinosternon subrubrum (N=7, mean mass SE=170 18 g) at was 5.10, andfor VCO was 3.40. These values are two temperatures 2 somewhat higher than those calculatedfor other turtle Parameter 20C30C species at the same temperature interval (Table 2), but fall well within the range of Q values reportedfor SMR VO (ml/h) 2.1070.35 9.2571.70 10 2 turtles at other temperature intervals. Some evidence SMR VCO2 (ml/h) 1.9670.22 6.3570.99 RQ 1.0670.17 0.7370.06 suggests that, in turtles, Q10 values are higher at cooler temperatures than at warmer temperatures, indicating that the rate of metabolic change is not isometric with 4. Discussion temperature. For example, the Q10 for box turtles (Terrapene ornata) between 10C and15 C was 54.38 As expected, temperature had a significant effect on comparedto 1.60 between 20 C and30 C(Gatten, metabolic rate in mudturtles. Turtles were more active 1974). Similarly, the Q10 for paintedturtles ( Chrysemys andhadsignificantly higher rates of VO 2 andVCO 2 at picta bellii) between 3 C and10 C was 8.5 comparedto 30C comparedto 20 C. Other studies that directly 2.9 between 15C and20 C(Herbert andJackson, testedthe relationship between temperature andmeta- 1985). A higher Q10 at cooler temperatures may reflect a bolic rate in turtles also founda strong positive transition from aerobic to anaerobic metabolism. Future relationship (e.g., Gatten, 1974; Hailey andLoveridge, work examining the effect of temperature on metabolic 1997; Steyermark andSpotila, 2000 ; Table 2). This is in rate in turtles should include a wide range of experi- agreement with the finding that, in vertebrate ec- mental temperatures andan examination of lactic acid totherms, metabolic rate generally increases with tem- accumulation to further test this hypothesis. perature (e.g., Gatten, 1974; Bennett andDawson, 1976 ; The RQ allows inference about the substrate usedto Beaupre et al., 1993; Karasov andAnderson,1998 ; fuel aerobic metabolism (Withers, 1992). An RQ value McNab, 2002). Unfortunately, most studies that report of 1.0 suggests oxidation of carbohydrate, an RQ of 0.84 ARTICLE IN PRESS 598 J.D. Litzgus, W.A. Hopkins / Journal of Thermal Biology 28 (2003) 595–600

Table 2 Q10 values basedon metabolic rates (oxygen consumption, VO 2) of turtles between 20 C and30 C. The studies included here reported standard metabolic rates or resting metabolic rates of fasted turtles as mass-speciﬁc rates. Note that Q10s from previous studies were calculatedusing the reportedSMR values in those studies

Species Temp VO2 VO2 Range of body Q10 Reference (C) (ml/h) (ml/g/h) mass (g)

Kinosternon subrubrum 20 2.10 0.0127 97–220 5.10 This study Kinosternon subrubrum 30 9.25 0.0557

Chelydra serpentina 20 — 0.0209 57–73 (juv) 2.49 Steyermark andSpotila (2000) Chelydra serpentina 30 — 0.0521

Trachemys scripta 20 — 0.0109 257–353 2.87 Gatten (1974) Trachemys scripta 30 — 0.0313

Terrapene ornata 20 — 0.0093 180–538 1.60 Gatten (1974) Terrapene ornata 30 — 0.0149

Kinixys spekii 20 — 0.0116 244–1383 3.35 Hailey andLoveridge(1997) Kinixys spekii 30 — 0.0389 indicates catabolism of protein, and a value of 0.7 relationship between body size and metabolic rate is suggests oxidation of lipid (Seidel, 1978; Withers, 1992). well documented among ectothermic animals (e.g. RQ values of mudturtles suggestedthat at 20 C, Bennett andDawson, 1976 ; Andrews and Pough, carbohydrate is the primary energy source utilized, and 1985; Feder and Burggren, 1992; McNab, 2002), and that at 30C, mainly lipids are oxidized to sustain with a larger sample size, we wouldhave likely detected metabolism. Similarly, in the congeneric yellow mud such a trend. Some studies of ectothermic vertebrates turtle (K. flavescens), the RQ was 0.7 at 28C, implying have also foundsignificant effects of sex on metabolism metabolism of lipids (Seidel, 1978). In snapping turtle (e.g., Taigen et al., 1985; Pough et al., 1992; Ryan and hatchlings (Chelydra serpentina), RQ values were lower Hopkins, 2000), whereas other studies have found no at about 0.64 at 15C and0.63 at 25 C (calculatedfrom effect of sex on metabolic rate (Beaupre et al., 1993; Table 3 in Steyermark andSpotila, 2000 ); however, Zaidan, 2003). In snakes as a group, it has been these values also implicate lipidas the primary metabolic suggestedthat males andnon-gravidfemales donot substrate. In addition, RQs between 20C and25 C for possess intrinsic differences in metabolic rates (Zaidan, the freshwater turtles Chelydra serpentina and Chrys- 2003). We did not find a significant difference between emys picta suggestedlipidcatabolism as the values were the sexes in metabolic rate; however, with respect to generally around0.7 ( Bennett andDawson, 1976 ). In the VCO2, males tended to have a higher metabolic rate tortoises Testudo graeca and T. hermanni, RQ values for than females. Our sample size for each gender was small body temperatures between 20C and25 C rangedfrom (N=3 females, N=4 males), so the lack of significance 0.7 to 0.91 (Bennett andDawson, 1976 ), implying that may simply reflect a lack of statistical power, andthus both lipidandprotein serve as metabolic substrates. additional work is needed to examine potential sex Similarly, others have notedthat resting andfasting effects on metabolism in turtles. reptiles exposedto a range of bodytemperatures Information on how metabolic rate varies with body generally have RQs near 0.7, implying catabolism of temperature can provide insight into individual varia- lipids (see Table XII in Bennett andDawson, 1976 ). tion in growth, reproduction, survival, and therefore, Body mass and sex are important sources of variance fitness. 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