Standardized ethograms and a device for assessing amphibian thermal responses in a warming world. (April 2020) - Meza-Parral, Yocoyani
Abstract: Most predictions of how populations and species of ectotherms will respond to global warming are based on estimates of the temperature at which organisms lose motor control ( i.e., CTmax - the Critical Thermal Maximum). Here, we describe a non-lethal protocol and ethograms to estimate the relative tolerance of amphibians to increasing temperatures. These methods—suitable for field or laboratory conditions—are replicable, inexpensive and applicable to both post-metamorphic stages and organisms with direct development. We illustrate the use of this standardized protocol for four amphibians from a tropical cloud forest in Veracruz, Mexico with contrasting life histories: a lungless salamander ( Aquiloeurycea cafetalera : Plethodontidae), a leaf-litter frog ( Craugastor rhodopis : Craugastoridae), a semiaquatic frog ( Lithobates berlandieri : Ranidae), and a tree frog ( Rheohyla miotympanum : Hylidae). We identified four behavioral responses preceding CTmax for all amphibians included in this study: 1) Optimal Activity Range, 2) Supra-optimal Activity Range, 3) Heat Stress Range, and 4) Involuntary Movements Range. Additionally, we identified a fifth parameter associated with resilience to heat shock: 5) Recovery Stage after reaching CTmax . We conclude that the behavioral responses preceding the Critical Thermal Maximum are as informative as CTmax . Using behavioral responses to estimate thermal tolerance has the additional advantage of reducing the risk of injury or death of amphibians during physiological experiments. Highlights: A portable and non-invasive device is proposed to study thermal ecology in amphibians. The device allowed to study post-metamorphic amphibians and with direct development. Four thermal ranges before Critical Thermal Maximum are identified. After experiments all study animals had a Recovery Stage.