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1. Evolved increases in hemoglobin-oxygen affinity and the Bohr effect coincided with the aquatic specialization of penguins

   https://doi.org/https://doi.org/10.1073/pnas.2023936118  

   Signore, Anthony V ; Tift, Michael S ; Hoffman, Federico G ; Schmitt, Todd L ; Moriyama, Hideaki ; Storz, Jay F. ( March 2021 , Proceedings of the National Academy of Sciences of the United States of America)

   Somero, George N. (Ed.)

   Dive capacities of air-breathing vertebrates are dictated by onboard O2 stores, suggesting that physiologic specialization of diving birds such as penguins may have involved adaptive changes in convective O2 transport. It has been hypothesized that increased hemoglobin (Hb)-O2 affinity improves pulmonary O2 extraction and enhances the capacity for breath-hold diving. To investigate evolved changes in Hb function associated with the aquatic specialization of penguins, we integrated comparative measurements of whole-blood and purified native Hb with protein engineering experiments based on site-directed mutagenesis. We reconstructed and resurrected ancestral Hb representing the common ancestor of penguins and the more ancient ancestor shared by penguins and their closest nondiving relatives (order Procellariiformes, which includes albatrosses, shearwaters, petrels, and storm petrels). These two ancestors bracket the phylogenetic interval in which penguin-specific changes in Hb function would have evolved. The experiments revealed that penguins evolved a derived increase in Hb-O2 affinity and a greatly augmented Bohr effect (i.e., reduced Hb-O2 affinity at low pH). Although an increased Hb-O2 affinity reduces the gradient for O2 diffusion from systemic capillaries to metabolizing cells, this can be compensated by a concomitant enhancement of the Bohr effect, thereby promoting O2 unloading in acidified tissues. We suggest that the evolved increase in Hb-O2 affinity in combination with the augmented Bohr effect maximizes both O2 extraction from the lungs and O2 unloading from the blood, allowing penguins to fully utilize their onboard O2 stores and maximize underwater foraging time. 

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2. A computed tomography ‐based survey of paramedullary diverticula in extant Aves

   https://doi.org/10.1002/ar.24923  

   Atterholt, Jessie ; Wedel, Mathew J. ( April 2022 , The Anatomical Record)

   Avian respiratory systems are comprised of rigid lungs connected to a hierarchically organized network of large, regional air sacs, and small diverticula that branch from them. Paramedullary diverticula are those that rest in contact with the spinal cord, and frequently invade the vertebral canal. Here, we review the historical study of these structures and provide the most diverse survey to date of paramedullary diverticula in Aves, consisting of observations from 29 taxa and 17 major clades. These extensions of the respiratory system are present in nearly all birds included in the study, with the exception of falconiforms, gaviiforms, podicipediforms, and piciforms. When present, they share connections most commonly with the intertransverse and supravertebral diverticula, but also sometimes with diverticula arising directly from the lungs and other small, more posterior diverticula. Additionally, we observed much greater morphological diversity of paramedullary airways than previously known. These diverticula may be present as one to four separate tubes (dorsal, lateral, or ventral to the spinal cord), or as a single large structure that partially or wholly encircles the spinal cord. Across taxa, paramedullary diverticula are largest and most frequently present in the cervical region, becoming smaller and increasingly absent moving posteriorly. Finally, we observe two osteological correlates of paramedullary diverticula (pneumatic foramina and pocked texturing inside the vertebral canal) that can be used to infer the presence of these structures in extinct taxa with similar respiratory systems.

    

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3. Architecture of the bronchial tree in Cuvier's dwarf caiman ( Paleosuchus palpebrosus )

   https://doi.org/10.1002/ar.24919  

   Schachner, Emma R. ; Diaz, Raul E. ; Coke, Rob ; Echols, Scott ; Osborn, Michelle L. ; Hedrick, Brandon P. ( April 2022 , The Anatomical Record)

   We imaged the lungs of five Cuvier's dwarf caiman (Paleosuchus palpebrosus) via computed tomography (CT) and micro‐computed tomography (μCT) and compared these data to the lungs of the American alligator (Alligator mississippiensis). These data demonstrate anatomical commonalities between the lungs ofP. palpebrosusandA. mississippiensis, and a few notable differences. The structural similarities are (a) a proximally narrow, distally widened, hook‐shaped primary bronchus; (b) a cervical ventral bronchus that branches of the primary bronchus and immediately makes a hairpin turn toward the apex of the lung; (c) a sequential series of dorsobronchi arising from the primary bronchus caudal to the cervical ventral bronchus; (d) intraspecifically highly variable medial sequence of secondary airways; (e) sac‐like laterobronchi; and (f) grossly dead‐ended caudal group bronchi in the caudal and ventral aspects of the lung. The primary differences between the two taxa are in the overall number of large bronchi (fewer inP. palpebrosus), and the number of branches that contribute to the cardiac regions. Imaging data of both a live and deceased specimen under varying states (postprandial, fasting, total lung capacity, open to atmosphere) indicate that the caudal margin and position of the lungs shift craniocaudally relative to the vertebral column. These imaging data suggest that the smooth thoracic ceiling may be correlated to visceral movement during ventilation, but this hypothesis warrants validation. These results provide the scaffolding for future comparisons between crocodilians, for generating preliminary reconstructions of the ancestral crocodilian bronchial tree, and establishing new hypotheses of bronchial homology across Archosauria.

    

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4. Blood oxygen transport and depletion in diving emperor penguins

   https://doi.org/10.1242/jeb.246832  

   Ponganis, Paul J. ; Williams, Cassondra L. ; Kendall-Bar, Jessica M. ( March 2024 , Journal of Experimental Biology)

   Oxygen store management underlies dive performance and is dependent on the slow heart rate and peripheral vasoconstriction of the dive response to control tissue blood flow and oxygen uptake. Prior research has revealed two major patterns of muscle myoglobin saturation profiles during dives of emperor penguins. In Type A profiles, myoglobin desaturated rapidly, consistent with minimal muscle blood flow and low tissue oxygen uptake. Type B profiles, with fluctuating and slower declines in myoglobin saturation, were consistent with variable tissue blood flow patterns and tissue oxygen uptake during dives. We examined arterial and venous blood oxygen profiles to evaluate blood oxygen extraction and found two primary patterns of venous hemoglobin desaturation that complemented corresponding myoglobin saturation profiles. Type A venous profiles had a hemoglobin saturation that (a) increased/plateaued for most of a dive's duration, (b) only declined during the latter stages of ascent, and (c) often became arterialized [arterio-venous (a-v) shunting]. In Type B venous profiles, variable but progressive hemoglobin desaturation profiles were interrupted by inflections in the profile that were consistent with fluctuating tissue blood flow and oxygen uptake. End-of-dive saturation of arterial and Type A venous hemoglobin saturation profiles were not significantly different, but did differ from those of Type B venous profiles. These findings provide further support that the dive response of emperor penguins is a spectrum of cardiac and vascular components (including a-v shunting) that are dependent on the nature and demands of a given dive and even of a given segment of a dive.

    

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5. Computational Fluid Dynamics Reveals a Unique Net Unidirectional Pattern of Pulmonary Airflow in the Savannah Monitor Lizard ( Varanus exanthematicus )

   https://doi.org/10.1002/ar.24293  

   Cieri, Robert L. ; Farmer, C. G. ( December 2019 , The Anatomical Record)

   This report models pulmonary airflow in the savannah monitor (Varanus exanthematicus) using computational fluid dynamics simulations, which are based on computed tomography data. Simulations were validated by visualizing the flow of aerosolized lipids in excised lungs with good but not perfect agreement. The lung of this lizard has numerous successive bronchi branching off a long intrapulmonary bronchus, which are interconnected by intercameral perforations. Unidirectional flow has been documented in the lateral secondary bronchi of the savannah monitor, but patterns of airflow in the rest of the lung remain unknown, hindering our understanding of the evolution of pulmonary patterns of airflow in tetrapods. These results indicate that the lung contains a unique net unidirectional flow, where the overall flow scheme is similar during expiration and late inspiration, but dissimilar during early inspiration. Air is transported net caudally through the intrapulmonary bronchus and net craniad through secondary bronchi, much like the pattern of flow in birds. The simulations show that many chambers feature flow in multiple directions during parts of the respiratory cycle, but some regions also show robust unidirectional airflow. Air moves craniad through secondary bronchi and between adjacent secondary bronchi through intercameral perforations. The first secondary bronchus, the hilar‐cranial bronchus, contains tidal flow that may improve ventilation of the central and dorsal lung parenchyma. These results expand our understanding of flow patterns in varanid lungs and suggest lungs with net unidirectional flow as an evolutionary pathway between tidal flow and complete unidirectional flow in multicameral lungs. Anat Rec, 2020. © 2019 American Association for Anatomy Anat Rec, 303:1768–1791, 2020. © 2019 American Association for Anatomy

    

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