The Comparison of Thermoregulation and Metabolism

Thermoregulation is an organism’s capability to maintain its body temperature and metabolism is the process in which energy is transformed within an organism’s body to maintain life. CSUSM comparative animal physiology students contained mice (Mus musculus) and Madagascar hissing cockroaches (Gromphadorhina portentosa) in vacuum tight contains to measure O2 consumption which would then translate into the mass specific metabolic rate (MSMR). With the comparison between mice in room and cold temperatures, mice held in cold temperatures had a higher MSMR (t= 3.23, df= 16, p= 0.005).

The MSMR of cockroaches held in cold temperatures resulted higher than cockroaches at room temperature (t= 1.87, df= 15, p= 0.081). Also, the mice held at both temperatures had a higher MSMR than the cockroaches at both temperatures. Since mice are endotherms, they would have a higher metabolic rate at colder temperatures due to increase consumption of O2 to produce heat and cockroaches would have lower metabolic rates because they are ectotherms and have a higher heat conductance. Introduction

Metabolism is the chemical reactions in which an organism utilizes energy to maintain life. Since glucose is a main source of energy, organisms use glucose along with oxygen to produce carbon dioxide, water and heat (Randall et al; 2002). Knowing this, metabolism can be measured by the production of CO2 or the consumption of O2. This is called indirect calorimetry (Randall et al; 2002).

Direct calorimetry is another method of metabolic activity but it is much harder to measure heat production released from an organism. Factors that can affect metabolic rate are temperature and body mass. For endotherms, or organisms that regulate their own body heat, tend to have higher metabolic rates and high and constant body temperatures (Bennett & Ruben, 1979). Alternatively, ectotherms, or organisms that gain heat from their external environment, tend to have lower metabolic rates and have lower and variable body temperatures (Bennett & Ruben, 1979).

Because endotherms must regulate their own constant body temperature and have higher metabolic rates, they must constantly be consuming energy and if ambient temperatures drop, endotherms must rely on their low conductance to heat and thermogenesis to keep their internal body temperature constant (Lu et al;1999; Berner,1999). As for ectotherms, because they at the mercy of the environment for heat, their mass specific metabolic rate is dependent on environmental temperature (Bennett & Ruben, 1979).

In this experiment, CSUSM students measured O2 consumption of mice (Mus musculus) and Madagascar hissing cockroaches (Gromphadorhina portentosa) by enclosing them in a vacuum tight container and placing them in ambient room temperature and cold temperatures. I hypothesized that mice held at a cold temperature would have a higher mass specific metabolic rate than mice held at cold temperatures because since mice are endotherms they have to use more energy, or use more O2, to maintain their constant optimal temperature.

Also, I hypothesized that the cockroaches held at room temperature would have a higher mass specific metabolic rate than the cockroaches held at cooler temperatures because since they are ectotherms, the lower the temperature the lower their metabolic rate will be. In addition, I hypothesized that mice held at room and cold temperature would have higher mass specific metabolic rate compared to the cockroaches held in both temperatures because mice have a lower conductance of heat. Methods

Procedure and methods were utilized from the Comparative Animal Physiology Laboratory Manual (Norris & Kristan, 2010). Four student t-tests were included in the statistical analysis. Results

In the mass specific metabolic rate (MSMR) comparison between mice tested in room temperature vs. cold temperatures (figure 1), mice measured at cold temperatures resulted in a higher rate (t= 3.23, df= 16, p= 0.005) but when the cockroaches were compared with respect to the two different temperatures (figure 1), cockroaches in cold temperature were found to have a higher MSMR (t= 1.87, df= 15, p= 0.081). In addition, the effects of endothermy were observed when the MSMR of mice kept in cold temperatures were higher than the MSMR of cockroaches held in cold temperatures (t= 9.52, df= 15, p<0.0001) (figure 1). Lastly, the MSMR of mice kept at room temperature were measured higher than the MSMR of the cockroaches at room temperature (t= 19.25, df= 16, p<0.0001) (figure 1). Discussion

Since the student t-tests demonstrated that mice held at cold temperatures had a higher MSMR when compared to those mice held at room temperature which supported the hypothesis, one can deduce that since mice are endotherms they must regulate their own internal temperature by using more O2 in order to maintain optimal a relatively constant and high body temperature (Berner, 1999). In contrast with the mice, the hypothesis was not supported by the result of the lower MSMR in the cockroaches held at room temperature, which was not the expected outcome because ectotherms conform to their environment and a lower MSMR in cold temperatures was expected.

This discrepancy could possibly be explained by a common characteristic of the cockroach species in that some cockroaches may display discontinuous ventilation patterns which could result in lower CO2 output or O2 consumption which in turn results in lower metabolic rates (Woodman et al; 2007). Lastly, the student t-tests conducted between the mice and cockroaches held in room and cold temperature resulted in a higher MSMR in the mice held at both temperatures because of the lower heat conductance attributed to endotherms (Bennett & Ruben, 1979). If an organism is able to keep their internal temperature constant, then a relatively constant MSMR can result. Since cockroaches are ectotherms, their heat conductance is high which results in a higher rate of losing heat which in turn results in a lower metabolic rate (Bennett & Ruben, 1979).