Thermal Acclimatization in Overwintering Tadpoles of the Green Frog, Lithobates clamitans (Latreille, 1801)

Abstract

Seasonal acclimatization permits organisms to maintain function in the face of environmental change. Tadpoles of the green frog (Lithobates clamitans) overwinter as tadpoles in much of their range. Because they are active in winter, we hypothesized that green frog tadpoles would display acclimatization of metabolic and locomotor function. We collected tadpoles in Sewanee, Tennessee (35.2°N) in winter and summer. Tadpoles collected during each season were tested at both winter (8°C) and summer (26°C) temperatures. Winter tadpoles were able to maintain swimming performance at both temperatures, whereas swimming performance decreased at cold temperatures in summer tadpoles. There was no evidence for seasonal acclimatization of whole-animal metabolic rate. Although whole-animal metabolic acclimatization was not observed, the activities of cytochrome c oxidase, citrate synthase, and lactate dehydrogenase measured in skeletal muscle homogenates showed higher activity in winter-acclimatized tadpoles indicating compensation for temperature. Further, the composition of muscle membranes of winter tadpoles had less saturated and more monounsaturated fatty acids and a higher ω-3 balance, unsaturation index, and peroxidation index than summer tadpoles. These data indicate that reversible phenotypic plasticity of thermal physiology occurs in larval green frog tadpoles. They appear to compensate for colder temperatures to maintain burst-swimming velocity and the ability to escape predators without the cost of maintaining a constant, higher standard metabolic rate in the winter.

Experimental depletion of gut microbiota diversity reduces host thermal tolerance and fitness under heat stress in a vertebrate ectotherm

“…The mechanisms underlying tadpole tolerance to cold likely differ, as studies in mice demonstrate that microbial products facilitate host maintenance of internal body temperature during cold exposure, which would not be important in ectothermic systems. Regardless, our result warrants future study and may impact animals in the wild, as green frogs often overwinter as tadpoles and can be exposed to near freezing temperatures 36 .…”

“…For all experiments, we used laboratory-reared tadpoles from wild adults of the green frog (Lithobates clamitans). Green frogs are an abundant and widespread anuran amphibian across eastern North America, and can adjust their physiology in response to temperature during both larval and adult lifestages 36, 37 . To manipulate the gut bacterial community, tadpoles were divided into two treatment groups: colonized and depleted.…”

“…After investigating thermal tolerance, fitness, and whole-organismal performance, we tested for differences between colonized and depleted tadpoles in several physiological metrics that may be associated with thermal tolerance to understand how the gut microbiome may impact thermal physiology at lower levels of biological organization, and what factors might underlie our results. The saturation of phospholipids in cell membranes and resulting changes in membrane fluidity is one biological mechanism that can contribute to thermal acclimation in ectotherms 6, 35, 36, 81–83 . Our study species, the green frog tadpole, has been previously shown to modulate phospholipid composition of cell membranes in response to temperature acclimation 36 .…”

“…The saturation of phospholipids in cell membranes and resulting changes in membrane fluidity is one biological mechanism that can contribute to thermal acclimation in ectotherms 6, 35, 36, 81–83 . Our study species, the green frog tadpole, has been previously shown to modulate phospholipid composition of cell membranes in response to temperature acclimation 36 . For example, winter acclimated tadpoles have higher proportions of unsaturated fatty acids in their muscles than summer acclimated tadpoles 36 .…”

“…Our study species, the green frog tadpole, has been previously shown to modulate phospholipid composition of cell membranes in response to temperature acclimation 36 . For example, winter acclimated tadpoles have higher proportions of unsaturated fatty acids in their muscles than summer acclimated tadpoles 36 . To probe if cell membrane composition may contribute to the differences in thermal phenotypes we observed between colonized and depleted tadpoles, we used LC-MS analysis to compare the composition of phospholipids in tail muscle tissue between colonized and depleted tadpoles from our first experiment, from a single acclimation temperature of 22°C.…”