A caseian point for the evolution of a diaphragm homologue among the earliest synapsids.

The origin of the diaphragm remains a poorly understood yet crucial step in the evolution of terrestrial vertebrates, as this unique structure serves as the main respiratory motor for mammals. Here, we analyze the paleobiology and the respiratory apparatus of one of the oldest lineages of mammal-like reptiles: the Caseidae. Combining quantitative bone histology and functional morphological and physiological modeling approaches, we deduce a scenario in which an auxiliary ventilatory structure was present in these early synapsids.

Lungs of the first amniotes: why simple if they can be complex?

We show-in contrast to the traditional textbook contention-that the first amniote lungs were complex, multichambered organs and that the single-chambered lungs of lizards and snakes represent a secondarily simplified rather than the plesiomorphic condition. We combine comparative anatomical and embryological data and show that shared structural principles of multichamberedness are recognizable in amniotes including all lepidosaurian taxa. Sequential intrapulmonary branching observed during early organogenesis becomes obscured during subsequent growth, resulting in a secondarily simplified, functionally single-chambered lung in lepidosaurian adults.

Evolution of air breathing: oxygen homeostasis and the transitions from water to land and sky.

Life originated in anoxia, but many organisms came to depend upon oxygen for survival, independently evolving diverse respiratory systems for acquiring oxygen from the environment. Ambient oxygen tension (PO2) fluctuated through the ages in correlation with biodiversity and body size, enabling organisms to migrate from water to land and air and sometimes in the opposite direction. Habitat expansion compels the use of different gas exchangers, for example, skin, gills, tracheae, lungs, and their intermediate stages, that may coexist within the same species; coexistence may be temporally disjunct (e.

Boundary conditions for heat transfer and evaporative cooling in the trachea and air sac system of the domestic fowl: a two-dimensional CFD analysis.

Various parts of the respiratory system play an important role in temperature control in birds. We create a simplified computational fluid dynamics (CFD) model of heat exchange in the trachea and air sacs of the domestic fowl (Gallus domesticus) in order to investigate the boundary conditions for the convective and evaporative cooling in these parts of the respiratory system. The model is based upon published values for respiratory times, pressures and volumes and upon anatomical data for this species, and the calculated heat exchange is compared with experimentally determined values for the domestic fowl and a closely related, wild species.

Morphometric partitioning of the respiratory surface area and diffusion capacity of the gills and swim bladder in juvenile Amazonian air-breathing fish, Arapaima gigas.

The gills and the respiratory swim bladders of juvenile specimens (mean body mass 100g) of the basal teleost Arapaima gigas (Cuvier 1829) were evaluated using stereological methods in vertical sections. The surface areas, harmonic mean barrier thicknesses and morphometric diffusing capacities for oxygen and carbon dioxide were estimated. The average respiratory surface area of the swim bladder (2173 cm² kg⁻¹) exceeded that of the gills (780 cm² kg⁻¹) by a factor of 2.

Biology of the sauropod dinosaurs: the evolution of gigantism.

The herbivorous sauropod dinosaurs of the Jurassic and Cretaceous periods were the largest terrestrial animals ever, surpassing the largest herbivorous mammals by an order of magnitude in body mass. Several evolutionary lineages among Sauropoda produced giants with body masses in excess of 50 metric tonnes by conservative estimates. With body mass increase driven by the selective advantages of large body size, animal lineages will increase in body size until they reach the limit determined by the interplay of bauplan, biology, and resource availability.

Respiration in a changing environment.

Multidisciplinary respiratory research highlighted in the present symposium uses existing and new models from all Kingdoms in both basic and applied research and bears upon molecular signaling processes that have been present from the beginning of life and have been maintained as an integral part of it. Many of these old mechanisms are still recognizable as ROS and oxygen-dependent pathways that probably were in place even before photosynthesis evolved. These processes are not only recognizable through relatively small molecules such as nucleotides and their derivatives.

The evolutionary origin of the mammalian diaphragm.

The comparatively low compliance of the mammalian lung results in an evolutionary dilemma: the origin and evolution of this bronchoalveolar lung into a high-performance gas-exchange organ results in a high work of breathing that cannot be achieved without the coupled evolution of a muscular diaphragm. However, despite over 400 years of research into respiratory biology, the origin of this exclusively mammalian structure remains elusive. Here we examine the basic structure of the body wall muscles in vertebrates and discuss the mechanics of costal breathing and functional significance of accessory breathing muscles in non-mammalian amniotes.

The anatomy of the respiratory system in Platysternon megacephalum Gray, 1831 (Testudines: Cryptodira) and related species, and its phylogenetic implications.

We discuss the morphology of the respiratory system regarding the phylogenetic relation among selected Testudines (Tetrapoda: Amniota). Lung structure and the associated coelomic organization are compared in Platysternon megacephalum and in representatives of the most-likely closely related taxa Chelydridae and Testudinoidea (Emydidae+Testudinidae). P.

Respiratory organs in wolf spiders: morphometric analysis of lungs and tracheae in Pardosa lugubris (L.) (Arachnida, Araneae, Lycosidae).

The respiratory system of the wolf spider Pardosa lugubris consists of a pair of well-developed lungs and four unbranched tube tracheae. We used stereological morphometric methods to investigate the morphological diffusing capacity of the lungs and of the walls of the tracheae ('lateral diffusing capacity'). We examined three groups of female P.

Morphometric analysis of the tracheal walls of the harvestmen Nemastoma lugubre (Arachnida, Opiliones, Nemastomatidae).

The tracheal system of harvestmen consists of two stem tracheae, which give rise to higher order tracheae that supply the extremities and internal organs. In this study, we used stereological morphometric methods to investigate diffusing capacities of the walls ('lateral diffusing capacity') of the tracheae of adult males and females of Nemastoma lugubre. Diffusing barriers of the tracheal walls tend to be thinnest (0.

Avian-like breathing mechanics in maniraptoran dinosaurs.

In 1868 Thomas Huxley first proposed that dinosaurs were the direct ancestors of birds and subsequent analyses have identified a suite of 'avian' characteristics in theropod dinosaurs. Ossified uncinate processes are found in most species of extant birds and also occur in extinct non-avian maniraptoran dinosaurs. Their presence in these dinosaurs represents another morphological character linking them to Aves, and further supports the presence of an avian-like air-sac respiratory system in theropod dinosaurs, prior to the evolution of flight.

Functional significance of the uncinate processes in birds.

The functional significance of the uncinate processes to the ventilatory mechanics of birds was examined by combining analytical modeling with morphological techniques. A geometric model was derived to determine the function of the uncinate processes and relate their action to morphological differences associated with locomotor specializations. The model demonstrates that uncinates act as levers, which improve the mechanical advantage for the forward rotation of the dorsal ribs and therefore lowering of the sternum during respiration.

Why respiratory biology? The meaning and significance of respiration and its integrative study.

Traditionally the process of respiration is divided into three phases: (1) cellular respiration, (2) transport of respiratory gases and (3) ventilation of the gas exchange organs (breathing). Thereby organisms assimilate chemical energy from the environment, and within their cells transfer it from molecule to molecule in a stepwise fashion. Although studied separately, these phases represent a continuum and cellular respiration in all life forms has much in common.

Deconvoluting lung evolution: from phenotypes to gene regulatory networks.

Speakers in this symposium presented examples of respiratory regulation that broadly illustrate principles of evolution from whole organ to genes. The swim bladder and lungs of aquatic and terrestrial organisms arose independently from a common primordial "respiratory pharynx" but not from each other. Pathways of lung evolution are similar between crocodiles and birds but a low compliance of mammalian lung may have driven the development of the diaphragm to permit lung inflation during inspiration.

Intestinal carbonic anhydrase, bicarbonate, and proton carriers play a role in the acclimation of rainbow trout to seawater.

Abrupt transfer of rainbow trout from freshwater to 65% seawater caused transient disturbances in extracellular fluid ionic composition, but homeostasis was reestablished 48 h posttransfer. Intestinal fluid chemistry revealed early onset of drinking and slightly delayed intestinal water absorption that coincided with initiation of NaCl absorption and HCO(3)(-) secretion. Suggestive of involvement in osmoregulation, relative mRNA levels for vacuolar H(+)-ATPase (V-ATPase), Na(+)-K(+)-ATPase, Na(+)/H(+) exchanger 3 (NHE3), Na(+)-HCO(3)(-) cotransporter 1, and two carbonic anhydrase (CA) isoforms [a general cytosolic isoform trout cytoplasmic CA (tCAc) and an extracellular isoform trout membrane-bound CA type IV (tCAIV)], were increased transiently in the intestine following exposure to 65% seawater.

Stereological estimation of surface area and barrier thickness of fish gills in vertical sections.

Previous morphometric methods for estimation of the volume of components, surface area and thickness of the diffusion barrier in fish gills have taken advantage of the highly ordered structure of these organs for sampling and surface area estimations, whereas the thickness of the diffusion barrier has been measured orthogonally on perpendicularly sectioned material at subjectively selected sites. Although intuitively logical, these procedures do not have a demonstrated mathematical basis, do not involve random sampling and measurement techniques, and are not applicable to the gills of all fish. The present stereological methods apply the principles of surface area estimation in vertical uniform random sections to the gills of the Brazilian teleost Arapaima gigas.

The coupled evolution of breathing and locomotion as a game of leapfrog.

Because the increase in metabolic rate related to locomotor activity places demands on the cardiorespiratory apparatus, it is not surprising that the evolution of breathing and of locomotion are coupled. As the respiratory faculty becomes more refined, increasingly aerobic life strategies can be explored, and this activity is in turn expedited by a higher-performance respiratory apparatus. This apparent leapfrogging of respiratory and locomotor faculties begins in noncraniate chordates and continues in water-breathing and air-breathing vertebrates.

Metabolic response to feeding in Tupinambis merianae: circadian rhythm and a possible respiratory constraint.

The diurnal tegu lizard Tupinambis merianae exhibits a marked circadian variation in metabolism that is characterized by the significant increase in metabolism during part of the day. These increases in metabolic rate, found in the fasting animal, are absent during the first 2 d after meal ingestion but reappear subsequently, and the daily increase in metabolic rate is added to the increase in metabolic rate caused by digestion. During the first 2 d after feeding, priority is given to digestion, while on the third and following days, the metabolic demands are clearly added to each other.