Rates of oxygen uptake increase independently of changes in heart rate in late stages of development and at hatching in the green iguana, Iguana iguana

The incubation environment does not explain significant variation in heart rate plasticity among avian embryos

The conditions an organism experiences during development can modify how they plastically respond to short-term changes in their environment later in life. This can be adaptive because the optimal average trait value and the optimal plastic change in trait value in response to the environment may differ across different environments. For example, early developmental temperatures can adaptively modify how reptiles, fish and invertebrates metabolically respond to temperature. However, whether individuals within populations respond differently (a prerequisite to adaptive evolution), and whether this occurs in birds, which are only ectothermic for part of their life cycle, is not known. We experimentally tested these possibilities by artificially incubating the embryos of Pekin ducks (Anas platyrhynchos domesticus) at constant or variable temperatures. We measured their consequent heart rate reaction norms to short-term changes in egg temperature and tracked their growth. Contrary to expectations, the early thermal environment did not modify heart rate reaction norms, but regardless, these reaction norms differed among individuals. Embryos with higher average heart rates were smaller upon hatching, but heart rate reaction norms did not predict subsequent growth. Our data also suggests that the thermal environment may affect both the variance in heart rate reaction norms and their covariance with growth. Thus, individual avian embryos can vary in their plasticity to temperature, and in contrast to fully ectothermic taxa, the early thermal environment does not explain this variance. Because among-individual variation is one precondition to adaptive evolution, the factors that do contribute to such variability may be important.

Embryonic and juvenile snakes (Natrix maura, Linnaeus 1758) compensate for high elevation hypoxia via shifts in cardiovascular physiology and metabolism

The colonization of novel environments requires a favorable response to conditions never, or rarely, encountered in recent evolutionary history. For example, populations colonizing upslope habitats must cope with lower atmospheric pressure at elevation, and thus reduced oxygen availability. The embryo stage in oviparous organisms is particularly susceptible, given its lack of mobility and limited gas exchange via diffusion through the eggshell and membranes. Especially little is known about responses of Lepidosaurian reptiles to reduced oxygen availability. To test the role of physiological plasticity during early development in response to high elevation hypoxia, we performed a transplant experiment with the viperine snake (Natrix maura, Linnaeus 1758). We maintained gravid females originating from low elevation populations (432 m above sea level [ASL]-normoxia) at both the elevation of origin and high elevation (2877 m ASL-extreme high elevation hypoxia; approximately 72% oxygen availability relative to sea level), then incubated egg clutches at both low and high elevation. Regardless of maternal exposure to hypoxia during gestation, embryos incubated at extreme high elevation exhibited altered developmental trajectories of cardiovascular function and metabolism across the incubation period, including a reduction in late-development egg mass. This physiological response may have contributed to the maintenance of similar incubation duration, hatching success, and hatchling body size compared to embryos incubated at low elevation. Nevertheless, after being maintained in hypoxia, juveniles exhibit reduced carbon dioxide production relative to oxygen consumption, suggesting altered energy pathways compared to juveniles maintained in normoxia. These findings highlight the role of physiological plasticity in maintaining rates of survival and fitness-relevant phenotypes in novel environments.

Morphological and physiological traits of the respiratory system in Iguana iguana and other non-avian reptiles

Functional morphology considers form and function to be intrinsically related. To understand organismal functions, a detailed knowledge of morphological and physiological traits is necessary. Regarding the respiratory system, the combined knowledge about pulmonary morphology and respiratory physiology is fundamental to understand how animals exchange gases and regulate critical functions to sustain metabolic activity. In the present study, the paucicameral lungs of Iguana iguana were analyzed morphometrically through stereological analysis using light and transmission electron images and compared with unicameral and multicameral lungs of six other non-avian reptiles. The morphological data were combined with physiological information to perform a principal component analysis (PCA) and phylogenetic tests of the relationship of the respiratory system. Iguana iguana, Lacerta viridis, and Salvator merianae presented similar pulmonary morphologies and physiologies when compared to Varanus examthematicus, Gekko gecko, Trachemys scripta, and Crocodylus niloticus. The former species showed an elevated respiratory surface area (%A_R), a high diffusion capacity, a low volume of total parenchyma (V_P), a low percentage of parenchyma concerning the lung volume (V_L), and a higher surface/volume ratio of the parenchyma (S_AR/V_P), with high respiratory frequency (f_R) and consequently total ventilation. The total parenchymal surface area (S_A), effective parenchymal surface-to-volume ratio (S_AR/V_P), respiratory surface area (S_AR), and anatomical diffusion factor (ADF) showed a phylogenetic signal, evidence that the morphological traits are more strongly correlated with the species' phylogeny than the physiological traits. In sum, our results indicated that the pulmonary morphology is intrinsically related to physiological traits of the respiratory system. Furthermore, phylogenetic signal tests also indicate that morphological traits are more likely to be evolutionary conserved than physiological traits, suggesting that evolutive physiological adaptations in the respiratory system could happen faster than morphological changes.

In vivo toxicity assessment of Remazol Gelb-GR (RG-GR) textile dye in zebrafish embryos/larvae (Danio rerio): Teratogenic effects, biochemical changes, immunohistochemical changes

Dyes, which are very important for various industries, have very adverse effects on the aquatic environment and aquatic life. However, there are limited studies on the toxic properties of dyes on living things. This research elucidated the sublethal toxicity of acute exposure of the textile dye remazol gelb-GR (RG-GR) using zebrafish embryos and larvae for 96 h. The 96 h-LC₅₀ for RG-GR in zebrafish embryos/larvae was determined to be 151.92 mg/L. Sublethal 96 hpf exposure was performed in RG-GR concentrations (0.5; 1.0; 10.0; 100.0 mg/L) to determine the development of toxicity in zebrafish embryos/larvae. RG-GR dye affected morphological development, and decreased heart rate, hatching, blood flow, and survival rates in zebrafish embryos/larvae. The immunopositivity of 8-hydroxy 2 deoxyguanosine (8-OHdG) in larvae exposed to RG-GR at high concentrations was found to be intense. Depending on the RG-GR dose increase, some biochemical parameters such as glutathione peroxidase (GSH) level, acetylcholinesterase (AChE) activity, catalase (CAT) activities, superoxide dismutase (SOD), and nuclear factor erythroid 2 (Nrf-2) levels were detected to be decreased in larvae, while malondialdehyde (MDA) content, nuclear factor kappa (NF-kB), tumor necrosis factor-α (TNF-α), DNA damage (8-OHdG level), interleukin-6 (IL-6) and apoptosis (Caspase-3) levels were found to be increased. The experimental results revealed that RG-GR dye has high acute toxicity on zebrafish embryo/larvae.

Nature vs. Nurture: Disentangling the Influence of Inheritance, Incubation Temperature, and Post-Natal Care on Offspring Heart Rate and Metabolism in Zebra Finches

A historic debate in biology is the question of nature vs. nurture. Although it is now known that most traits are a product of both heredity (“nature”) and the environment (“nurture”), these two driving forces of trait development are rarely examined together. In birds, one important aspect of the early developmental environment is egg incubation temperature. Small changes (<1°C) in incubation temperature can have large effects on a wide-array of offspring traits. One important trait is metabolism, because it is related to life-history traits and strategies, organismal performance, and energetic and behavioral strategies. Although it has been shown that embryonic and post-hatch metabolism are related to egg incubation temperature, little is known about how this may vary as a function of genetic differences or post-hatching environmental conditions. Here, we investigated this question in zebra finches (Taeniopygia guttata). We experimentally incubated eggs at two different temperatures: 37.5°C (control), which is optimal for this species and 36.3°C (low), which is suboptimal. We first measured embryonic heart rate as a proxy of embryonic metabolic rate. Then, at hatch, we cross-fostered nestlings to differentiate genetic and pre-hatching factors from post-hatching environmental conditions. When offspring were 30 days-old, we measured their resting metabolic rate (RMR; within the thermoneutral zone) and thermoregulatory metabolic rate (TMR; 12°C; birds must actively thermoregulate). We also measured RMR and TMR of all genetic and foster parents. We found that embryonic heart rate was greater in eggs incubated at the control temperature than those at the low temperature. Further, embryonic heart rate was positively related to genetic father RMR, suggesting that it is both heritable and affected by the pre-natal environment. In addition, we found that post-hatch metabolic rates were positively related to genetic parent metabolic rate, and interactively related to incubation temperature and foster mother metabolic rate. Altogether, this suggests that metabolism and the energetic cost of thermoregulation can be influenced by genetics, the pre-natal environment, and the post-natal environment. Our study sheds light on how environmental changes and parental care may affect avian physiology, as well as which traits may be susceptible to natural selection.

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 heart rate correlates with maternal temperature and developmental stage in viviparous snakes

Interactions between the environment and maternal and embryonic physiology can have critical ramifications for early-life phenotypes and survival in a range of species. A major component of the environment-maternal-embryonic nexus is the regulation of embryonic heart rate, which can have important ramifications for developmental phenology, but remains relatively unexplored in viviparous reptiles. The goal of this study was to test for a relationship between embryonic heart rate and maternal body temperature in two species of viviparous garter snakes. The embryonic heart rates of Thamnophis elegans and T. sirtalis were assessed using a field-portable ultrasound. For both T. elegans and T. sirtalis, embryonic heart rate was strongly correlated to maternal temperature. Interestingly, there was also a strong correlation between embryonic and maternal heart rate that was most likely mediated by a common response to maternal body temperature, in spite of the effects of handling during ultrasound on maternal heart rate. Furthermore, embryos at earlier developmental stages had lower heart rates. To our knowledge, this study is the first to explore embryonic heart rate in viviparous reptiles, providing a foundation for future work using ultrasonography to test ecological and evolutionary hypotheses related to developmental dynamics in free-ranging viviparous species.

High temperatures limit developmental resilience to high-elevation hypoxia in the snake Natrix maura (Squamata: Colubridae)

Climate change is generating range shifts in many organisms, notably along the altitudinal gradient. However, moving up in altitude exposes organisms to lower oxygen availability, which may negatively affect development and fitness, especially at high temperatures. To test this possibility in a potentially upward-colonizing species, we artificially incubated developing embryos of the viperine snake Natrix maura Linnaeus 1758, using a split-clutch design, in conditions of extreme high elevation or low elevation at two ecologically-relevant incubation temperatures (24 and 32 °C). Embryos at low and extreme high elevations incubated at cool temperatures did not differ in development time, hatchling phenotype or locomotor performance. However, at the warmer incubation temperature and at extreme high elevation, hatching success was reduced. Further, embryonic heart rates were lower, incubation duration longer and juveniles born smaller. Nonetheless, snakes in this treatment were faster swimmers than siblings in other treatment groups, suggesting a developmental trade-off between size and performance. Constraints on development may be offset by the maintenance of important performance metrics, thus suggesting that early life-history stages will not prevent the successful colonization of high-elevation habitat even under the dual limitations of reduced oxygen and increased temperature.

High-elevation hypoxia impacts perinatal physiology and performance in a potential montane colonizer

Climate change is generating range shifts in many organisms, notably along the elevational gradient in mountainous environments. However, moving up in elevation exposes organisms to lower oxygen availability, which may reduce the successful reproduction and development of oviparous organisms. To test this possibility in an upward‐colonizing species, we artificially incubated developing embryos of the viperine snake (Natrix maura) using a split‐clutch design, in conditions of extreme high elevation (hypoxia at 2877 m above sea level; 72% sea‐level equivalent O₂ availability) or low elevation (control group; i.e. normoxia at 436 m above sea level). Hatching success did not differ between the two treatments. Embryos developing at extreme high elevation had higher heart rates and hatched earlier, resulting in hatchlings that were smaller in body size and slower swimmers compared to their siblings incubated at lower elevation. Furthermore, post‐hatching reciprocal transplant of juveniles showed that snakes which developed at extreme high elevation, when transferred back to low elevation, did not recover full performance compared to their siblings from the low elevation incubation treatment. These results suggest that incubation at extreme high elevation, including the effects of hypoxia, will not prevent oviparous ectotherms from producing viable young, but may pose significant physiological challenges on developing offspring in ovo. These early‐life performance limitations imposed by extreme high elevation could have negative consequences on adult phenotypes, including on fitness‐related traits.

Blood flow distribution in embryonic common snapping turtles Chelydra serpentina (Reptilia; Chelonia) during acute hypoxia and α-adrenergic regulation

Embryonic turtles have four distinct vascular beds that separately perfuse the developing embryo's body and the extra-embryonic yolk sac, amnion and chorioallantoic membrane (CAM). The mechanisms enabling differential regulation of blood flow through these separate beds, in order to meet the varying demands of the embryo during development, is of current interest. The present investigation followed the changes in blood flow distribution during an acute exposure to hypoxia and after α-adrenergic blockade. We monitored heart rate (f_H), mean arterial pressure (P_m), and determined relative blood flow distribution (%Q̇sys) using colored microspheres. At 70% and 90% of the incubation period hypoxia elicited a bradycardia without changing P_m while %Q̇sys was altered only at 70%, increasing to the CAM and liver. Blockade of α-adrenergic responses with phentolamine did not change f_H or P_m but increased %Q̇sys to the shell. These results show the capacity of embryos to redistribute cardiac output during acute hypoxia, however α-adrenergic receptors seemed to play a relatively small role in embryonic cardiovascular regulation.

Transplanting gravid lizards to high elevation alters maternal and embryonic oxygen physiology, but not reproductive success or hatchling phenotype

Increased global temperatures have opened previously inhospitable habitats, such as at higher elevations. However, the reduction of oxygen partial pressure with increase in elevation represents an important physiological constraint that may limit colonization of such habitats, even if the thermal niche is appropriate. To test the mechanisms underlying the response to ecologically-relevant levels of hypoxia, we performed a translocation experiment with the common wall lizard (Podarcis muralis), a widespread European lizard amenable to establishing populations outside its natural range. We investigated the impacts of hypoxia on the oxygen physiology and reproductive output of gravid common wall lizards and the subsequent development and morphology of their offspring. Lowland females transplanted to high elevations increased their haematocrit and haemoglobin concentration within days and maintained routine metabolism compared to lizards kept at native elevations. However, transplanted lizards suffered from increased reactive oxygen metabolite production near the oviposition date, suggesting a cost of reproduction at high elevation. Transplanted females and females native to different elevations did not differ in reproductive output (clutch size, egg mass, relative clutch mass, or embryonic stage at oviposition) or in post-oviposition body condition. Developing embryos reduced heart rates and prolonged incubation times at high elevations within the native range and at extreme high elevations beyond the current range, but this reduced oxygen availability did not affect metabolic rate, hatching success, or hatchling size. These results suggest that this opportunistic colonizer is capable of successfully responding to novel environmental constraints in these important life-history stages.

Copper inhibits hatching of fish embryos via inducing reactive oxygen species and down-regulating Wnt signaling

The copper ion (Cu²⁺) has been reported to suppress the hatching of fish. However, little is known about the underlying mechanism. In this study, copper nanoparticles (CuNPs) and Cu²⁺ were shown to significantly suppress hatching of zebrafish in a dosage-dependent manner, and reactive oxygen species (ROS) scavengers NAC (N-acetylcysteine) & GSH (reduced glutathione) and Wnt signaling agonist BIO (6-bromoindirubin-3'-oxime) significantly alleviated the suppressing effects of Cu²⁺ and CuNPs on egg hatching. Mechanistically, NAC, GSH, and BIO recovered the egg hatching in copper-treated group via increasing the embryonic motility rather than stimulating the expression and secretion of hatching enzymes before hatching. Additionally, no significant difference in egg hatching was observed between the control and Cu²⁺-treated group at 72 hpf (hours post fertilization) in cox17 mutant embryos, in which little ROS was producd after copper stimulation. This may be the first report that Cu²⁺ and CuNPs suppress embryonic motility and the subsequent hatching via inducing ROS and at the same time down-regulating Wnt signaling in fish embryos.

Convective oxygen transport during development in embryos of the snapping turtle Chelydra serpentina

This study investigated the maturation of convective oxygen transport in embryos of the snapping turtle (Chelydra serpentina). Measurements included: mass, oxygen consumption (VO2), heart rate (fH), blood oxygen content and affinity and blood flow distribution at 50%, 70% and 90% of the incubation period. Body mass increased exponentially, paralleled by increased cardiac mass and metabolic rate. Heart rate was constant from 50% to 70% of incubation but was significantly reduced at 90%. Hematocrit (Hct) and hemoglobin concentration (Hb) were constant at the three points of development studied but arteriovenous difference (A-V diff) doubled from 50 to 90% of incubation. Oxygen affinity was lower early in 50% of incubation compared to all other age groups. Blood flow was directed predominantly to the embryo but highest to the CAM at 70% incubation and was directed away from the yolk as it was depleted at 90% incubation. The findings indicate that the plateau or reduction in egg VO2 characteristic of the late incubation period of turtle embryos may be related to an overall reduction in mass-specific VO2 that is correlated with decreasing relative heart mass and plateaued CAM blood flow. Importantly, if the blood properties remain unchanged prior to hatching, as they did during the incubation period studied in the current investigation, this could account for the pattern of VO2 previously reported for embryonic snapping turtles prior to hatching.