The influence of acute temperature oscillations on the cardiorespiratory function, control and efficiency of a Neotropical teleost: the trahira (Hoplias malabaricus)

• Grant number: 20/04335-0
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: August 01, 2020
• End date: July 31, 2023
• Field of knowledge: Biological Sciences - Physiology - Compared Physiology
• Principal Investigator: Carlos Arturo Navas Iannini
• Grantee: Vinicius Araújo Armelin
• Host Institution: Instituto de Biociências (IB). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Climate change is causing large modifications in distribution and population structures of living organisms due to the influence of temperature on its bodily functions (e.g. increase in global temperature or its wider and more frequent oscillations). To understand, predict and mitigate such influence, we need investigations on the effects of temperature on the homeostatic regulation of physiological systems in different organisms. There is much evidence that the thermal tolerance of ectotherms is linked to the ability of these animals in sustaining their basal physiological functions, and some academic effort has been placed on describing the failure of cardiorespiratory system to meet the bodily demands for oxygen at high temperatures. However, these approaches have largely neglected underlying mechanisms of cardiorespiratory regulation that support the integrity of the oxygen extraction and transport cascade and orchestrate adequate tissue oxygen delivery - such as baroreceptor and chemoreceptor reflexes. Specifically, the baroreflex promotes cardiovascular adjustments that maintain satisfactory blood pressure and flow to the animals' respiratory surface and bodily tissues, supporting gas exchange and the supply of general cellular needs. The chemoreflex, on the other hand, promotes cardiorespiratory adjustments that quickly matches oxygen uptake and carbon dioxide elimination with the instantaneous tissue demands. Both baroreflex and chemoreflex are mediated by short-acting neurohumoral activity, and recent evidence points to a certain susceptibility of this activity to temperature changes. In this context, the present proposal aims to test the hypothesis that acute increases (to supra-optimal temperatures) or decreases (to sub-optimal temperatures) in temperature reduce the efficiency of the mechanisms of cardiorespiratory regulation in teleosts (notably the baroreceptor and chemoreceptor reflexes), jeopardizing the cardiovascular and respiratory effectiveness in meeting the aerobic demands. To do this, specimens of trahira (Hoplias malabaricus) acclimated in optimal thermal condition (25°C) will be divided into three experimental groups that will be evaluated for 1 hour in optimal temperature (25°C) and for 24 hours after: (1) maintaining the optimal temperature (group 25°C; N = 10); (2) an acute temperature change to supra-optimal value (group 35°C; N = 10); and (3) an acute temperature change to sub-optimal value (group 15°C; N = 10). Throughout the exposures to optimal, supra-optimal and sub-optimal temperatures, the animals' metabolism, cardiorespiratory function and efficiency in meeting the aerobic demands, baroreflex function and efficiency, chemoreflex function and efficiency, and cardiorespiratory neurohumoral control will be continuously evaluated through the acquisition of 25 distinct physiological variables - which will allow a profound and unprecedented phenological investigation on the influence of acute fluctuations in ambient temperature on the ability of these animals to sustain their basal aerobic functions. (AU)