We studied the role of plasma glucose concentration on individuals of Rhinella spinulosa in response to annual temperature variation and freezing temperatures. Measurements and collection of toads were made every 2 mo for a period of 1 yr. To determine whether toads were exposed to low temperatures in their habitat, we proceeded with the study of operating temperatures (Te). The measures of operating temperature were determined by using plaster models placed in the field, simulating the situation where toads are outside or inside shelters, for which it was determined that individuals in the winter season would have been exposed to temperatures below 0°C. Glucose levels measured in field specimens showed an annual variation, but laboratory specimens exposed to freezing temperatures had higher plasma glucose levels than field toads. Furthermore, the crystallization temperature for the species has been recorded at -1.6°C. The increase in glucose concentration indicates its possible use as a cryoprotectant before freezing events in this species of frogs and also in the coldest months at temperatures below 0°C.
Keywords: cryoprotectant; crystallization temperature; glucose; low temperatures; operating temperatures.