Analysis of heart rate control to assess thermal sensitivity responses in Brazilian toads.

J.E.S Natali,J.G Chauí-Berlinck,V.H Rodrigues,B.T Santos

doi:10.1590/1414-431x20143875

Abstract

In anurans, changes in ambient temperature influence body temperature and, therefore, energy consumption. These changes ultimately affect energy supply and, consequently, heart rate (HR). Typically, anurans living in different thermal environments have different thermal sensitivities, and these cannot be distinguished by changes in HR. We hypothesized that Rhinella jimi (a toad from a xeric environment that lives in a wide range of temperatures) would have a lower thermal sensitivity regarding cardiac control than R. icterica (originally from a tropical forest environment with a more restricted range of ambient temperatures). Thermal sensitivity was assessed by comparing animals housed at 15° and 25°C. Cardiac control was estimated by heart rate variability (HRV) and heart rate complexity (HRC). Differences in HRV between the two temperatures were not significant (P=0.214 for R. icterica and P=0.328 for R. jimi), whereas HRC differences were. All specimens but one R. jimi had a lower HRC at 15°C (all P<0.01). These results indicate that R. jimi has a lower thermal sensitivity and that cardiac control is not completely dependent on the thermal environment because HRC was not consistently different between temperatures in all R. jimi specimens. This result indicates a lack of evolutive trade-offs among temperatures given that heart rate control at 25°C is potentially not a constraint to heart rate control at 15°C.

Highlights

Animals regulate or change their body temperature in response to ambient temperature, and changes in energy demands accompany this process
Braz J Med Biol Res 48(1) 2015 www.bjournal.com.br anurans often face wide temperature variation in their habitats and present mechanisms of heart rate (HR) control similar to mammals, it is relevant to quantitatively investigate cardiac control as a means of adaptation to thermal stress. The significance of such a marker becomes even more clear considering that HRs occurring at different temperatures are unreliable to distinguish between two Bufonidae species with putatively different thermal sensitivities (i.e., HR does not seem to be linearly or related to ambient temperature) [7]
Because locomotor performance is usually adjusted to ecologically relevant ranges of temperature in anurans [9], species living in different thermal environments might exhibit different HR control

Summary

Introduction

Animals regulate or change their body temperature in response to ambient temperature, and changes in energy demands accompany this process. Braz J Med Biol Res 48(1) 2015 www.bjournal.com.br anurans often face wide temperature variation in their habitats and present mechanisms of HR control similar to mammals, it is relevant to quantitatively investigate cardiac control as a means of adaptation to thermal stress The significance of such a marker (i.e., cardiac control) becomes even more clear considering that HRs occurring at different temperatures are unreliable to distinguish between two Bufonidae species with putatively different thermal sensitivities (i.e., HR does not seem to be linearly or related to ambient temperature) [7]. Because locomotor performance (an energy demanding system) is usually adjusted to ecologically relevant ranges of temperature in anurans [9], species living in different thermal environments might exhibit different HR control. This is the first study of thermal sensitivity from the perspective of HR control

Material and Methods

Results

Discussion