Oral Presentations - Session 2D: UC 332
Do Big Beetle Larvae Run Big Thermal Risks?
Presentation Type
Presentation
Faculty Mentor’s Full Name
H. Arthur Woods
Faculty Mentor’s Department
Biological Sciences
Abstract / Artist's Statement
Extremes of body size captivate biologists. In insects, the lack of extant giants has prompted the question, what is constraining insect size? While multiple physiological and ecological hypotheses have been presented, there is no widely accepted explanation. One unexplored physiological hypothesis is that large insects are unable to shed metabolic heat rapidly enough and are at increased risk of overheating. My project examines this idea using larvae of the Japanese rhinoceros beetle (Trypoxylus dichotomus), chosen for their huge size, simple body plan, and underground lifestyle. Using CO2 respirometry, I measured larval metabolic rates at room temperature. Although these beetle larvae are among the largest insects ever measured, their metabolic rates fell squarely on the expected values extrapolated from other, smaller insects. This permitted me to build a simple mathematical model of heat balance for insects across a wide range of body sizes. Specifically, I converted my measured rates of gas exchange into rates of metabolic heat production, and used the model to predict how much equilibrium body temperature would increase in insects larger than naturally occur. I then used CO2 respirometry during temperature ramping experiments to determine thermal tolerance limits. This showed that larvae could survive temperatures of 46-48˚C. Together, these show that for every 100-g increase in body size, there is a 0.5˚C increase in equilibrium body temperature, and that body temperatures are predicted to be well below the thermal maximum for animals ten times larger than any extant insect. In addition, larvae placed on runways extending across a thermal gradient were surprisingly active, and clearly capable of behavioral thermoregulation through movement to cooler locations. Collectively, my results suggest that insect size is not limited by metabolic heat production. This study provides a greater understanding of insect size constraints and behaviors associated with thermal regulation.
Category
Life Sciences
Do Big Beetle Larvae Run Big Thermal Risks?
UC 332
Extremes of body size captivate biologists. In insects, the lack of extant giants has prompted the question, what is constraining insect size? While multiple physiological and ecological hypotheses have been presented, there is no widely accepted explanation. One unexplored physiological hypothesis is that large insects are unable to shed metabolic heat rapidly enough and are at increased risk of overheating. My project examines this idea using larvae of the Japanese rhinoceros beetle (Trypoxylus dichotomus), chosen for their huge size, simple body plan, and underground lifestyle. Using CO2 respirometry, I measured larval metabolic rates at room temperature. Although these beetle larvae are among the largest insects ever measured, their metabolic rates fell squarely on the expected values extrapolated from other, smaller insects. This permitted me to build a simple mathematical model of heat balance for insects across a wide range of body sizes. Specifically, I converted my measured rates of gas exchange into rates of metabolic heat production, and used the model to predict how much equilibrium body temperature would increase in insects larger than naturally occur. I then used CO2 respirometry during temperature ramping experiments to determine thermal tolerance limits. This showed that larvae could survive temperatures of 46-48˚C. Together, these show that for every 100-g increase in body size, there is a 0.5˚C increase in equilibrium body temperature, and that body temperatures are predicted to be well below the thermal maximum for animals ten times larger than any extant insect. In addition, larvae placed on runways extending across a thermal gradient were surprisingly active, and clearly capable of behavioral thermoregulation through movement to cooler locations. Collectively, my results suggest that insect size is not limited by metabolic heat production. This study provides a greater understanding of insect size constraints and behaviors associated with thermal regulation.