Metabolic and respiratory chemosensitivity and brain monoaminergic responses to cold exposure in chicks subjected to thermal manipulation during incubation.

We evaluated ventilation (V˙E), body temperature (TB), oxygen consumption (V˙ O2), respiratory equivalent (V˙E/ V˙ O2), and monoamine concentrations of 14-day-old (14d) male and female chicks from eggs incubated at low (LT, 36 °C), control (CT, 37.5 °C) and high (HT, 39 °C) temperature during the early embryonic phase, to normoxia, hypercapnia and hypoxia under exposure to cold environment (20 °C). At normoxia, acute cold exposure did not affect the ventilatory variables, with the exception of HT males, in which cold prevented the reduced V˙E observed under thermoneutral conditions. Exposure to 20 °C caused a decrease in TB in both sexes, and LT and HT females presented a greater hypothermic response. Hypercapnia combined with cold did not alter the ventilatory variables, but LT females and CT males and females showed a blunted CO2-induced hyperventilation due to a higher V˙ O2, compared to the same groups in thermoneutral conditions. Unlike with thermoneutral conditions, the blunted hypercapnic hyperventilation observed in the HT groups was not observed during cold challenge. CO2 exposure promoted a similar decrease in TB in the thermoneutral and acutely cold exposed groups, while LT females under cold condition presented a blunted hypothermic response. During hypoxia, cold challenge attenuated the increase in V˙E in LT females and HT males, due to changes in VT. Hypoxic metabolic depression was greater in LT females and males and HT males during cold exposure, while no change in V˙E/ V˙ O2 was observed. The only alteration in monoaminergic concentration under cold challenge was an increase in brainstem 5-HIAA and 5-HIAA/5-HT ratio in HT females, and an enhanced 5-HT concentration in HT males. In summary, thermal manipulation during embryogenesis induces 14d old chicks to respond differently to cold stress with LT females and HT males being more sensitive.

Seasonal variation of hypoxic and hypercarbic ventilatory responses in the lizard Tropidurus torquatus.

Carbon dioxide (CO2) and oxygen (O2) influence the breathing pattern of reptiles, especially when CO2 is in excess or O2 at low concentrations and the effects of these gases on the respiratory response varies according to the species. In addition to respiratory gases, seasonal changes can also modulate breathing pattern and ventilatory responses to hypoxia and hypercarbia. Therefore, the present study investigated the breathing pattern and ventilatory responses to hypercarbia (5% CO2) and hypoxia (5% O2) of the Neotropical lizard Tropidurus torquatus over a period of one year, covering all seasons (summer, autumn, winter and spring). Our data suggest that like other ectothermic sauropsids, Tropidurus torquatus possesses distinct ventilatory responses to hypoxia and hypercarbia, being more sensitive to changes in CO2 than in O2. Additionally, the ventilatory responses to hypoxia were more pronounced during summer and hypercanic and pos-hypercapnic ventilatory response was reduced during spring, suggesting that seasonality modulates the control of ventilation in this species.

Heat stress affects breathing and metabolism of chicks incubated at high temperature.

Global warming poses serious implications to animal physiology and a gradual increase in ambient temperature affects all living organisms, particularly fast-growing selected species. We recorded ventilation (V̇E), body temperature (TB), oxygen consumption (V̇O2) and respiratory equivalent (V̇E/V̇O2) of 14-day-old (14d) male and female chicks at room air conditions, hypercapnia and hypoxia at heat stress (HS, 32 °C). These chicks had previously been exposed to control (CI, 37.5 °C) and high (HI, 39 °C) temperatures during the first 5 days of incubation. Under resting conditions, acute HS increased V̇E in HI females but not in HI males. Hypercapnia combined with heat promoted a potentiation of CO2-hyperventilatory response in HI females when compared with thermoneutral condition, whereas in HI incubated males a hypoventilation under hypercapnia and heat stress was observed compared to the CI group. Hypoxia associated with heat stress increased V̇E only in HI females. Our data indicates that females are more sensitive to thermal manipulation during incubation and it seems that the thermal embryonic manipulation, at least during the first days of development, does not improve the adaptive response of chicks to heat stress.

Thermal Acclimation to the Highest Natural Ambient Temperature Compromises Physiological Performance in Tadpoles of a Stream-Breeding Savanna Tree Frog.

Amphibians may be more vulnerable to climate-driven habitat modification because of their complex life cycle dependence on land and water. Considering the current rate of global warming, it is critical to identify the vulnerability of a species by assessing its potential to acclimate to warming temperatures. In many species, thermal acclimation provides a reversible physiological adjustment in response to temperature changes, conferring resilience in a changing climate. Here, we investigate the effects of temperature acclimation on the physiological performance of tadpoles of a stream-breeding savanna tree frog (Bokermannohyla ibitiguara) in relation to the thermal conditions naturally experienced in their microhabitat (range: 18.8-24.6°C). We quantified performance measures such as routine and maximum metabolic rate at different test (15, 20, 25, 30, and 34°C) and acclimation temperatures (18 and 25°C). We also measured heart rate before and after autonomic blockade with atropine and sotalol at the respective acclimation temperatures. Further, we determined the critical thermal maximum and warming tolerance (critical thermal maximum minus maximum microhabitat temperature), which were not affected by acclimation. Mass-specific routine and mass-specific maximum metabolic rate, as well as heart rate, increased with increasing test temperatures; however, acclimation elevated mass-specific routine metabolic rate while not affecting mass-specific maximum metabolic rate. Heart rate before and after the pharmacological blockade was also unaffected by acclimation. Aerobic scope in animals acclimated to 25°C was substantially reduced, suggesting that physiological performance at the highest temperatures experienced in their natural habitat is compromised. In conclusion, the data suggest that the tadpoles of B. ibitiguara, living in a thermally stable environment, have a limited capacity to physiologically adjust to the highest temperatures found in their micro-habitat, making the species more vulnerable to future climate change.

Embryonic Thermal Manipulation Affects Ventilation, Metabolism, Thermal Control and Central Dopamine in Newly Hatched and Juvenile Chicks.

The first third of incubation is critical for embryonic development, and environmental changes during this phase can affect the physiology and survival of the embryos. We evaluated the effects of low (LT), control (CT), and high (HT) temperatures during the first 5 days of incubation on ventilation ( V . E ), body temperature (Tb), oxygen consumption ( V . O2), respiratory equivalent ( V . E / V . O2), and brain monoamines on 3-days-old (3d) and 14-days-old (14d) male and female chickens. The body mass of LT animals of both ages and sexes was higher compared to HT and CT animals (except for 3d males). The heart mass of 14d HT animals was higher than that of CT animals. Thermal manipulation did not affect V . E , V . O2 or V . E / V . O2 of 3d animals in normoxia, except for 3d LT males V . E , which was lower than CT. Regarding 14d animals, the HT females showed a decrease in V . E and V . O2 compared to CT and LT groups, while the HT males displayed a lower V . O2 compared to CT males, but no changes in V . E / V . O2. Both sexes of 14d HT chickens presented a greater Tb compared to CT animals. Thermal manipulations increased the dopamine turnover in the brainstem of 3d females. No differences were observed in ventilatory and metabolic parameters in the 3d animals of either sexes, and 14d males under 7% CO2. The hypercapnic hyperventilation was attenuated in the 14d HT females due to changes in V . O2, without alterations in V . E . The 14d LT males showed a lower V . E , during hypercapnia, compared to CT, without changes in V . O2, resulting in an attenuation in V . E / V . O2. During hypoxia, 3d LT females showed an attenuated hyperventilation, modulated by a higher V . O2. In 14d LT and HT females, the increase in V . E was greater and the hypometabolic response was attenuated, compared to CT females, which resulted in no change in the V . E / V . O2. In conclusion, thermal manipulations affect hypercapnia-induced hyperventilation more so than hypoxic challenge, and at both ages, females are more affected by thermal manipulation than males.

Cardiorespiratory and thermal responses to hypercapnia in chickens exposed to CO2 during embryonic development.

The concentration of CO2 in the environment surrounding the embryo impacts development and may also influence the cardiorespiratory responses after hatching. Therefore, we aimed to evaluate the cardiorespiratory and thermal responses to hypercapnia in chicks that were exposed to CO2 during embryonic development, i.e., incubation. Embryos were incubated without and with a gradual increase in CO2 concentration up to 1 % during the first ten days of incubation. Ten-day-old chicks (males and females) were again acutely exposed to hypercapnia (7 % CO2), or to room air (normocapnia) and pulmonary ventilation, arterial pH and blood gases, arterial blood pressure and heart rate, body temperature (Tb) and oxygen consumption (V⋅O2) were measured. Compared to control animals, male chicks incubated with 1 % CO2 presented an attenuated ventilatory response to hypercapnia (P < 0.05), whereas no difference was found in the hypercapnic ventilatory response in both female chick groups (0 % vs 1 % CO2 incubation). Hypercapnia induced bradycardia in all groups (P < 0.001). The CO2 exposure during incubation did not alter the cardiovascular responses to hypercapnia in post-hatch animals. There were no significant effects of incubation treatment (0 % vs 1 % CO2) or sex in the mean arterial pressure, Tb, and V⋅O2 of animals in normocapnia and hypercapnia. As for the V⋅E/V⋅O2, hypercapnia caused an increase in both groups (P < 0.05), regardless of incubation treatment. In conclusion, among cardiorespiratory and metabolic variables, the ventilatory response to hypercapnia can be attenuated by pre-exposure to 1 % CO2 during embryonic development, especially in male chicks up to 10 days.