Effect of temperature fluctuations on larval function of the Baja California chorus frog, Pseudacris hypochondriaca

Abstract

Environmental temperature has an extensive impact on the phenotypes of all animals.Temperature fluctuations, often experienced naturally across daily or longer cycles, may cause profound effects on physiological phenotypes of animals, particularly during development and in ectotherms like amphibians. This study tested this hypothesis by evaluating the effects of temperature fluctuations during the larval development of the eurythermal Baja California chorus frog (Pseudacris hypochondriaca), a species native to southern California and northern Baja California. Eggs were collected from ponds in San Marcos, California within 24 hours of fertilization and separated into four temperature treatments: 15°C constant, and fluctuating treatments over 24 hours of 12.5°C – 17.5°C, 10°C – 20°C, and 15°C – 25°C. Oxygen consumption rate (V̇o2), critical thermal maximum (CTMAX), and swim speed were measured for tadpoles at 15°C during hindlimb toe development. Relative to mass‐specific V̇o2 in 15°C constant tadpoles, mass‐specific V̇o2 measured at 15°C showed a slight increase in 12.5°C – 17.5°C tadpoles, a larger increase in 10°C – 20°C tadpoles, but no difference in 15°C – 25°C tadpoles. Relative to CTMAX in 15°C constant tadpoles, CTMAX was similar in 12.5°C – 17.5°C tadpoles, slightly higher in 10°C – 20°C tadpoles, and greatly increased in 15°C – 25°C tadpoles. Swim speed measured at 15°C was similar across all temperature treatments. Overall, greater fluctuations had stronger effects on larval V̇o2 and CTMAX, and tadpoles tend to acclimate to higher temperatures during daily cycles. Acclimation in thermal tolerance and metabolic rates of this eurythermal amphibian indicates the animals will likely show plasticity in some traits in response to fluctuating temperatures. Future studies will examine these traits across a range of acute measurement temperatures to fully understand the functional implications of fluctuating temperatures.