Buccal Pump Research Articles

Novel rebreathing adaptation extends dive time in a semi-aquatic lizard.

Bubble use evolved in many small invertebrates to enable underwater respiration, but, until recently, there has been no evidence that vertebrate animals use bubbles in a similar manner. Only one group of vertebrates, semi-aquatic Anolis lizards, may be an exception: these lizards dive underwater when threatened and, while underwater, rebreathe a bubble of air over their nostrils. Although it seems that rebreathing should be adaptive, possibly functioning to extend the time that lizards remain in underwater refugia, this has not been empirically tested. Here, I demonstrate that rebreathing serves to extend dive time in a semi-aquatic anole, Anolis aquaticus. I prevented the formation of normal rebreathing bubbles by applying a commercial emollient on the skin surface where bubbles form to assess the impact of bubbles on rebreathing cycles, gular pumps, and dive times. Lizards that were allowed to rebreathe normally remained underwater an average of 32% longer than those with impaired rebreathing, suggesting a functional role of rebreathing in underwater respiration. Unlike rebreathing, gular pumping was unaffected by treatment and may warrant further research regarding its role in supplementing underwater respiration. This study provides evidence that vertebrates can use bubbles to respire underwater and raises questions about adaptive mechanisms and potential bio-inspired applications.

An electrophysiological correlate of sleep in a shark.

Sleep is a prominent physiological state observed across the animal kingdom. Yet, for some animals, our ability to identify sleep can be masked by behaviors otherwise associated with being awake, such as for some sharks that must swim continuously to push oxygenated seawater over their gills to breathe. We know that sleep in buccal pumping sharks with clear rest/activity cycles, such as draughtsboard sharks (Cephaloscyllium isabellum, Bonnaterre, 1788), manifests as a behavioral shutdown, postural relaxation, reduced responsiveness, and a lowered metabolic rate. However, these features of sleep do not lend themselves well to animals that swim nonstop. In addition to video and accelerometry recordings, we tried to explore the electrophysiological correlates of sleep in draughtsboard sharks using electroencephalography (EEG), electromyography, and electrooculography, while monitoring brain temperature. The seven channels of EEG activity had a surprising level of (apparent) instability when animals were swimming, but also when sleeping. The amount of stable EEG signals was too low for replication within- and across individuals. Eye movements were not measurable, owing to instability of the reference electrode. Based on an established behavioral characterization of sleep in draughtsboard sharks, we offer the original finding that muscle tone was strongest during active wakefulness, lower in quietly awake sharks, and lowest in sleeping sharks. We also offer several critical suggestions on how to improve techniques for characterizing sleep electrophysiology in future studies on elasmobranchs, particularly for those that swim continuously. Ultimately, these approaches will provide important insights into the evolutionary confluence of behaviors typically associated with wakefulness and sleep.

Air Breathing and Suction Feeding Kinematics in the West African Lungfish, Protopterus annectens.

Research on the water-to-land transition tends to focus on the locomotor changes necessary for terrestriality. However, the evolution from water breathing to air breathing was also a necessary precursor to the invasion of land. Air is approximately 1000 times less dense and 50 times less viscous, and contains hundreds of times more oxygen than water. However, unlike the transition to terrestrial locomotion, breathing air does not require body weight support, so the evolution of air breathing may have necessitated smaller changes to morphology and function. We used X-ray reconstruction of moving morphology to compare the cranial kinematics of aquatic buccal pumping, such as that seen in suction feeding, with the aerial buccal pumping required for lung ventilation in the West African lungfish (Protopterus annectens). During buccal pumping behaviors, the cranial bones and associated soft tissues act as valves and pumps, and the sequence of their motions controls the pattern of fluid flow. Both behaviors are characterized by an anterior-to-posterior wave of expansion and an anterior-to-posterior wave of compression. We found that the pectoral girdle and cranial rib rotate consistently during air breathing and suction feeding, and that the muscle between them shortens during buccal expansion. Overall, we conclude that the major cranial bones maintain the same basic functions (i.e., acting as valves or pumps, or transmitting power) across aquatic and aerial buccal pumping. The cranial morphology that enables aquatic buccal pumping is well suited to perform air breathing and accommodates the physical differences between air and water.

Behavioural sleep in two species of buccal pumping sharks (Heterodontus portusjacksoni and Cephaloscyllium isabellum).

Sleep is known to occur in most, if not all, animals studied thus far. Recent studies demonstrate the presence of sleep in flatworms and jellyfish, suggesting that this behaviour evolved early in the evolution of animals. Sharks are the earliest known extant, jawed vertebrates and may play an important role in understanding the evolutionary history of sleep in vertebrates, and yet, it is unknown whether they sleep. The Port Jackson (Heterodontus portusjacksoni) and draughtsboard (Cephaloscyllium isabellum) sharks are both benthic, buccal pumping species and remain motionless for extended periods of time. Whether these periods of prolonged inactivity represent sleep or quiet wakefulness is unknown. A key criterion for separating sleep from other quiescent states is an increased arousal threshold. We show here that inactive sharks of both species require significantly higher levels of electric stimulation before they show a visible response. Sharks deprived of rest, however, show no significant compensatory increase in restfulness during their normal active period following enforced swimming. Nonetheless, increased arousal thresholds in inactive animals suggest that these two species of shark sleep - the first such demonstration for members of this group of vertebrates. Further research, including electrophysiological studies, on these and other sharks, is required for a comprehensive understanding of sleep in cartilaginous fishes.

Diverse Activity Rhythms in Sharks (Elasmobranchii).

Sharks are an interesting group of vertebrates, as many species swim continuously to "ram" oxygen-rich seawater over their gills (ram ventilators), whereas other species "pump" seawater over their gills by manipulating buccal cavity volume while remaining motionless (buccal pumpers). This difference in respiratory physiology raises the question: What are the implications of these differences in lifestyle for circadian rhythms? We investigated the diel activity patterns of 5 species of sharks, including 3 ram ventilating species: the school shark (Galeorhinus galeus), the spotted estuary smooth-hound (Mustelus lenticulatus), and the spiny dogfish (Squalus acanthias); and 2 buccal pumping species: the Port Jackson (Heterodontus portusjacksoni) and draughtsboard (Cephaloscyllium isabellum) sharks. We measured the amount, duration, and distance traveled while swimming over multiple days under a 12:12 light:dark light regime for all species and used modified light regimes for species with a clear diel rhythm in activity. We identified a surprising diversity of activity rhythms. The school shark and smooth-hound swam continuously; however, whereas the school shark swam at the same speed and covered the same distance during the day and night, the smooth-hound swam slower at night and traversed a shorter distance. A similar pattern was observed in the spiny dogfish, although this shark swam less overall. Both the Port Jackson and draughtsboard sharks showed a marked nocturnal preference for swimming. This pattern was muted and disrupted during constant light and constant dark regimes, although circadian organization of this pattern was maintained under certain conditions. The consequences of these patterns for other biological processes, such as sleep, remain unclear. Nonetheless, these 5 species demonstrate remarkable diversity within the activity rhythms of sharks.

The effect of gillnet capture on the metabolic rate of two shark species with contrasting lifestyles

In this study we investigated the metabolic consequences of simulated gillnet capture in species with contrasting life-history characteristics, the gummy shark, Mustelus antarcticus and the Port Jackson shark, Heterdontus portusjacksoni. Pre-stress standard and routine metabolic rates (MR) of individuals of these species were measured and compared to the MR obtained after simulated gillnet capture. Standard MRs of M. antarcticus and H. portusjacksoni were 168.5 ± 61.9 mgO2 kg-0.67 h−1 and 144.1 ± 20.4 mgO2 kg-0.67 h−1, respectively. Routine MRs of M. antarcticus and H. portusjacksoni were 202.6 ± 63.5 mgO2 kg-0.67 h−1 and 166.4 ± 11.2 mgO2 kg-0.67 h−1, respectively. The simulated gillnet-capture treatment decreased the MR of M. antarcticus by 59.3% and increased that of H. portusjacksoni by 21.6%. Our results confirm that M. antarcticus is highly sensitive to gillnet capture, exhibiting significant variability in MR among individuals and also a high delayed mortality rate. We interpret the decrease in MR as a compensatory mechanism for reducing oxygen consumption to cope with the stress imposed by capture. Mortality in this species was associated with higher pre-stress MR, and lower post-stress MR. In contrast, H. portusjacksoni showed mild increases in MR. Their resilience to capture stress most likely relies on effective buccal pumping and lower basal MR. A mixed-effects model approach permitted us to identify the main sources of variation in the MR measured, which were the individual differences, treatment effects, species variations and delayed mortality. The comparative approach employed in this work allowed us to understand and provide reliable estimates of the effects of fishing on the MRs of these two species.

Palaeophysiology of pH regulation in tetrapods.

The involvement of mineralized tissues in acid-base homeostasis was likely important in the evolution of terrestrial vertebrates. Extant reptiles encounter hypercapnia when submerged in water, but early tetrapods may have experienced hypercapnia on land due to their inefficient mode of lung ventilation (likely buccal pumping, as in extant amphibians). Extant amphibians rely on cutaneous carbon dioxide elimination on land, but early tetrapods were considerably larger forms, with an unfavourable surface area to volume ratio for such activity, and evidence of a thick integument. Consequently, they would have been at risk of acidosis on land, while many of them retained internal gills and would not have had a problem eliminating carbon dioxide in water. In extant tetrapods, dermal bone can function to buffer the blood during acidosis by releasing calcium and magnesium carbonates. This review explores the possible mechanisms of acid-base regulation in tetrapod evolution, focusing on heavily armoured, basal tetrapods of the Permo-Carboniferous, especially the physiological challenges associated with the transition to air-breathing, body size and the adoption of active lifestyles. We also consider the possible functions of dermal armour in later tetrapods, such as Triassic archosaurs, inferring palaeophysiology from both fossil record evidence and phylogenetic patterns, and propose a new hypothesis relating the archosaurian origins of the four-chambered heart and high systemic blood pressures to the perfusion of the osteoderms. This article is part of the theme issue 'Vertebrate palaeophysiology'.

Foregut Development and Metamorphosis in a Pyramidellid Gastropod: Modularity and Constraint within a Complex Life Cycle.

Pyramidellids are tiny ectoparasitic gastropods with highly derived feeding structures for piercing and sucking. We attempted to resolve homology controversies about unique pyramidellid feeding structures by examining foregut development through larval and metamorphic stages, using sections for light and electron microscopy. We anticipated that, like many marine invertebrate larvae, post-metamorphic structures would differentiate extensively in late larvae to speed metamorphic transition. Previous studies of gastropods suggested that development of juvenile feeding structures in larvae was facilitated by foregut subdivision into dorsal and ventral developmental modules, and spatial uncoupling of these modules may have facilitated adaptive radiation in neogastropods. Observations of Odostomia tenuisculpta suggested that the stylet may be derived from cuticle-secreting buccal epithelium surrounding the proximal end of the salivary duct, whereas the stylet sheath could be either a derived jaw or a radular tooth. The anterior half of the remarkable buccal pump of these euthyneuran gastropods develops from the larval esophagus, which is unorthodox compared to caenogastropods, where extensive post-metamorphic specialization of a dorsal module component has not been previously described. The introvert tube develops from pouches of the distal larval esophagus and may actually be an eversible oral tube rather than an acrembolic proboscis. Minimal differentiation of presumptive juvenile foregut structures occurred during the larval stage of O. tenuisculpta, when compared to other gastropods. The stylet, stylet sheath, and buccal pump may be incompatible with functioning of the larval esophagus; thus, an explosive period of morphogenesis is necessary at metamorphosis. Although dorsal and ventral modules were recognizable during the development of O. tenuisculpta, we failed to find evidence that this modularity facilitated the extreme evolutionary remodeling of post-metamorphic feeding structures.

Buccal jet streaming and dead space determination in the South American lungfish, Lepidosiren paradoxa

The “jet stream” model predicts an expired flow within the dorsal part of the buccal cavity with small air mixing during buccal pump ventilation, and has been suggested for some anuran amphibians but no other species of air breathing animal using a buccal force pump has been investigated. The presence of a two-stroke buccal pump in lungfish, i.e. expiration followed by inspiration, was described previously, but no quantitative data are available for the dead-space of their respiratory system and neither a detailed description of airflow throughout a breathing cycle. The present study aimed to assess the degree of mixing of fresh air and expired gas during the breathing cycle of Lepidosiren paradoxa and to verify the possible presence of a jet stream during expiration in this species. To do so, simultaneous measurements of buccal pressure and ventilatory airflows were carried out. Buccal and lung gases (PCO2 and PO2) were also measured. The effective ventilation was calculated and the dead space estimated using Bohr equations. The results confirmed that the two-stroke buccal pump is present in lungfish, as it is in anuran amphibians. The present approaches were coherent with a small dead space, with a very small buccal-lung PCO2 difference. In the South American lungfish the dead space (VD) as a percentage of tidal volume (VT) (VD / VT) ranged from 4.1 to 12.5%. Our data support the presence of a jet stream and indicate a small degree of air mixing in the buccal cavity. Comparisons with the literature indicate that these data are similar to previous data reported for the toad Rhinella schneideri.

Filter-foraging strategies of captive American paddlefish (Polyodon spathula) in relation to food type, density and distribution in the water column

The American paddlefish (Polyodon spathula) forages using ram filter-feeding to feed on (mainly) zooplankton throughout the water column. It makes an ontogenetic transition from buccal pumping to ram ventilation feeding in the first year. In wild conditions plankton is often distributed unevenly in time and space, however this does not always apply to captive conditions. In the study presented here two paddlefish were fed on a range of diets and supply methods to see if they would alter their foraging strategy. Insight in influencing foraging strategies could be beneficial for zoos and aquariua for display purposes or for improving welfare conditions. The paddlefish were studied during foraging and foraging strategy, bout length and usage of the aquarium space were recorded. Three foraging strategies can be distinguished: foraging while swimming in straight lines, foraging while swimming in circulatory paths and particulate foraging. Although these strategies appear to not have a fixed switch-point, a significant difference can be found between the foraging strategies for starting a certain strategy and ending it in relation to food density (p=<0.003). Mean time spent on a strategy differs in duration from 1 to 60 seconds. When negative buoyant food sources (e.g. Mysis) were used, the paddlefish foraged in the lower parts of the aquarium. Neutrally buoyant food sources (e.g. Daphnia pulex) caused the paddlefish to forage throughout different depths of the aquarium. (p=<0.001).

Respiratory motoneuron properties during the transition from gill to lung breathing in the American bullfrog.

Amphibian respiratory development involves a dramatic metamorphic transition from gill to lung breathing and coordination of distinct motor outputs. To determine whether the emergence of adult respiratory motor patterns was associated with similarly dramatic changes in motoneuron (MN) properties, we characterized the intrinsic electrical properties of American bullfrog trigeminal MNs innervating respiratory muscles comprising the buccal pump. In premetamorphic tadpoles (TK stages IX-XVIII) and adult frogs, morphometric analyses and whole cell recordings were performed in trigeminal MNs identified by fluorescent retrograde labeling. Based on the amplitude of the depolarizing sag induced by hyperpolarizing voltage steps, two MN subtypes (I and II) were identified in tadpoles and adults. Compared with type II MNs, type I MNs had larger sag amplitudes (suggesting a larger hyperpolarization-activated inward current), greater input resistance, lower rheobase, hyperpolarized action potential threshold, steeper frequency-current relationships, and fast firing rates and received fewer excitatory postsynaptic currents. Postmetamorphosis, type I MNs exhibited similar sag, enhanced postinhibitory rebound, and increased action potential amplitude with a smaller-magnitude fast afterhyperpolarization. Compared with tadpoles, type II MNs from frogs received higher-frequency, larger-amplitude excitatory postsynaptic currents. Input resistance decreased and rheobase increased postmetamorphosis in all MNs, concurrent with increased soma area and hyperpolarized action potential threshold. We suggest that type I MNs are likely recruited in response to smaller, buccal-related synaptic inputs as well as larger lung-related inputs, whereas type II MNs are likely recruited in response to stronger synaptic inputs associated with larger buccal breaths, lung breaths, or nonrespiratory behaviors involving powerful muscle contractions.

Eye Movements in Frogs and Salamanders-Testing the Palatal Buccal Pump Hypothesis.

SynopsisIn frogs and salamanders, movements of the eyeballs in association with an open palate have often been proposed to play a functional role in lung breathing. In this “palatal buccal pump,” the eyeballs are elevated during the lowering of the buccal floor to suck air in through the nares, and the eyeballs are lowered during elevation of the buccal floor to help press air into the lungs. Here, we used X-Ray Reconstruction of Moving Morphology to investigate eye movements during lung breathing and feeding in bullfrogs and axolotls. Our data do not show eye movements that would be in accordance with the palatal buccal pump. On the contrary, there is a small passive elevation of the eyeballs when the buccal floor is raised. Inward drawing of the eyeballs occurs only during body motion and for prey transport in bullfrogs, but this was not observed in axolotls. Each eye movement in bullfrogs has a vertical, a mediolateral, and an anteroposterior component. Considering the surprisingly weak posterior motion component of the eyeballs, their main role in prey transport might be fixing the prey by pressing it against the buccal floor. The retraction of the buccal floor would then contribute to the posterior push of the prey. Because our study provides no evidence for a palatal buccal pump in frogs and salamanders, there is also no experimental support for the idea of a palatal buccal pump in extinct temnospondyl amphibians, in contrast to earlier suggestions.

A rare new species of Corambe Bergh, 1869 (Mollusca: Gastropoda: Nudibranchia) from the Caribbean Sea, with a review of the taxonomical history of the Corambidae Bergh, 1871

The taxonomic history of the family Corambidae Bergh, 1871 is extremely complex, in part due to the rarity of some of the taxa within the family, but also because of their unusual morphology. Some species, particularly in the Atlantic, seem to be very rare, while others are abundant, widely distributed, and having large lists of synonyms. Corambe obscura (A. E. Verril, 1870) is one of these species that has been considered to have many synonyms, which conferred it a vast range of distribution. The recent re-capture and reinstatement of Corambe carambola (Marcus, 1955) meant a severe restriction of the distribution of C. obscura and a reminder that a lot of questions are still to be answered regarding the Atlantic species of the genus. In this work, a rare species of Corambe Bergh, 1869 is described using a single specimen from Guadeloupe, Caribbean Sea. Corambe osculabundus Ortea & Caballer sp. nov. was collected during the expedition KARUBENTHOS coordinated by the Museum national d’Histoire naturelle, in Paris. It is characterized by a pattern of red lipstick-shaped stains that cover the mantle, hemispherical spiculous tubercles, a posterior notch on the mantle, rhinophores with anterolateral expansions, a dorsal buccal pump, 14 gill leafs (central gill leaf absent), and a radular formula 42 × 1.1-2P.2.1.0.1.2.1-2P.1., with one or two smooth plates interspersed before the outermost lateral teeth. The taxonomic history of the nudibranch family Corambidae is synthesized in an attempt to assess the identity of potential rare species that may have been synonymized in the absence of fresh material.

Central control of air breathing in fishes

The diversity of sites and surfaces that are utilized for gas transfer from air to blood in fish is remarkable. While a few species do utilize their gills for gas exchange in air, this is a rare occurrence and most air-breathing fish utilize other surfaces including air-breathing organs and lungs. At present almost nothing is known about the central sites that initiate and regulate air breathing although hypotheses can be put forward based on our rudimentary understanding of the sites involved in water breathing in lampreys and teleost fishes, and those involved in air breathing in pre-metamorphic anuran ampibians. The pumps involved in producing both water and air breathing in fishes are highly conserved, a buccal pump, assisted by pharyngeal and/or parabranchial/opercular pumps, produce both forms of ventilation. What varies between species are the manner in which air breaths are produced (in two versus four phases), and the ‘valving’ involved in producing water flow over the gills versus air flow in and out of air-breathing organs. The latter suggests that a major step in the evolution of air breathing was the evolution of the mechanisms that control the flow of the respiratory medium. The neural matrix that underlies the co-ordination of the pump and the valving events remains enigmatic and in much need of further research.

Captive Birth of Tiger Shark (Galeocerdo cuvier) Reveals a Shift in Respiratory Mode during Parturition

Ram ventilation, which is characterized by the production of a respiratory water current over the gill by locomotory effort, widely occurs among pelagic sharks. However, the process by which the juvenile starts this respiratory mechanism remains largely unknown. The captive birth of a Tiger Shark (Galeocerdo cuvier) at the Okinawa Churaumi Aquarium on 23 March 2017 permitted the examination of the parturition process and behavior of newborn juveniles of this species. Sonographic examination of the pregnant female showed that, unlike adult Tiger Sharks, embryos used buccal pumping, revealing that Tiger Shark shifts its respiratory mechanism from buccal pumping to ram ventilation after birth. Our observation also showed that ram ventilation of the neonate was not continuous, and buccal pumping was also used when the neonate intermittently rested on the bottom of the tank. We speculate that this behavior is the transitional phase in the shift from buccal pumping to ram ventilation in neonates, and continuous ram ventilation may be established after the development of continuous and fast swimming abilities.

Effects of vagotomy and pharmacological blocking on heart rate of the toad Rhinella arenarum (Anura: Bufonidae) during forced submersion

Toads of Rhinella (=Bufo) arenarum were subjected to a condition of forced submersion duringa 40-minute period, to deepen the understanding of the mechanisms involved in the control ofboth submersion and emersion. Animals previously submitted to a first control measurementseries, were then injected with atropine or propranolol, or were vagotomized. In animals eitherinjected with atropine or vagotomized, a higher heart rate (HR) than in the control group wasobserved, before, during and after the forced submersion. These animals were able to decreaseHR, although in a lesser extent than controls, suggesting that other mechanisms in addition tovagal activity are also producing and maintaining bradycardia during the submersion period.In those animals injected with propranolol (a β-adrenergic blocker), a HR lower than that ofcontrols were observed only at the beginning of the submersion and during the emersion phase.The low HR caused by propranolol during emersion with buccal pumping shows the importanceof the sympathetic system in increasing HR during emersion.

The dipnoan buccal pump reconstructed in 3D and implications for air breathing in Devonian lungfishes

AbstractLungfishes are known for, and indeed take their name from, their bimodal respiratory abilities. All three extant genera can use their lungs to extract oxygen from the atmosphere, although their reliance upon this capability differs among taxa. Lungs are considered primitive for the Osteichthyes, however the distinctive buccal pump mode of air gulping exhibited by extant lungfishes appears to be a specialization. It is associated with a number of derived skeletal characters (cranial ribs, long parasphenoid stalk, midline gap between palatal tooth plates) that first appeared during the Devonian. These have been described individually, but in no Devonian lungfish has their three-dimensional (3D) spatial relationship been reconstructed and analyzed. Here we present the 3D morphology ofRhinodipterus, a Mid-Late Devonian lungfish from Australia and Europe, based on synchrotron tomography and conventional microtomography scans.Unlike less crownward contemporaneous lungfishes such asGriphognathusandChirodipterus,Rhinodipterushas a full set of skeletal buccal pump components that can be directly compared to those of extant lungfishes, suggesting that it made more extensive use of air breathing than other Gogo or Bergisch Gladbach genera. This is interesting in relation to the environmental context as Gogo and Bergisch Gladbach are both marine, contrasting with the frequently hypoxic tropical to subtropical fresh water environments inhabited by modern lungfishes. The evolution of buccal pump-supported lung ventilation was evidently not necessarily associated with a transition to non-marine habitats.

CO2-metabolism in early tetrapods revisited: inferences from osteological correlates of gills, skin and lung ventilation in the fossil record

One of the most important physiological changes during the conquest of land by vertebrates was the increasing reliance on lung breathing, with the concomitant decrease in importance of gill breathing. The main problem involved here was to cope with the excessive accumulation of CO2 in the body and to avoid respiratory acidosis. In the past, several often mutually contradicting hypotheses of CO2-elimination via skin, lungs and gills in early tetrapods have been proposed, based on theoretical physiological considerations and comparison with extant air-breathing fishes and amphibians. This study proposes a revised scenario of CO2-elimination in early tetrapods based on fossil evidence, that is recently identified osteological correlates of gills, skin structure and mode of lung ventilation. In stem tetrapods of the Devonian and Carboniferous, O2-uptake via the lungs by buccal pumping was decoupled from CO2-release via internal gills, and the rather gas-impermeable skin played a minor role in gaseous exchange. The two main lineages of crown-group tetrapods, the amphibian and amniote lineage, used different strategies of CO2-elimination. As in stem tetrapods, O2-uptake and CO2-release remained always largely decoupled in temnospondyls, which ventilated their lungs via buccal pumping and relied mainly on their internal gills for CO2-release. Temnospondyls were not able to reduce their internal gills before their skin became more gas permeable and their body size was reduced, to shift from internal gills to the skin as the major site of CO2-elimination, a pattern that is retained in most lissamphibians. In contrast, internal gills were lost very early in stem amniote evolution. This was associated with the evolution of the more effective aspiration pump that allowed the elimination of the bulk of CO2 via the lungs, leading to a coupled O2-uptake and CO2-loss in stem amniotes and later in amniotes.

Origins, Innovations, and Diversification of Suction Feeding in Vertebrates

We review the origins, prominent innovations, and major patterns of diversification in suction feeding by vertebrates. Non-vertebrate chordates and larval lamprey suspension-feed by capturing small particles in pharyngeal mucous. In most of these lineages the gentle flows that transport particles are generated by buccal cilia, although larval lamprey and thaliacean urochordates have independently evolved a weak buccal pump to generate an oscillating flow of water that is powered by elastic recovery of the pharynx following compression by buccal muscles. The evolution of jaws and the hyoid facilitated powerful buccal expansion and high-performance suction feeding as found today throughout aquatic vertebrates. We highlight three major innovations in suction feeding. Most vertebrate suction feeders have mechanisms that occlude the corners of the open mouth during feeding. This produces a planar opening that is often nearly circular in shape. Both features contribute to efficient flow of water into the mouth and help direct the flow to the area directly in front of the mouth's aperture. Among several functions that have been identified for protrusion of the upper jaw, is an increase in the hydrodynamic forces that suction feeders exert on their prey. Protrusion of the upper jaw has evolved five times in ray-finned fishes, including in two of the most successful teleost radiations, cypriniforms and acanthomorphs, and is found in about 60% of living teleost species. Diversification of the mechanisms of suction feeding and of feeding behavior reveals that suction feeders with high capacity for suction rarely approach their prey rapidly, while slender-bodied predators with low capacity for suction show the full range of attack speeds. We hypothesize that a dominant axis of diversification among suction feeders involves a trade-off between the forces that are exerted on prey and the volume of water that is ingested.

Automated high-throughput measurement of body movements and cardiac activity of Xenopus tropicalis tadpoles

Xenopus tadpoles are an emerging model for developmental, genetic and behavioral studies. A small size, optical accessibility of most of their organs, together with a close genetic and structural relationship to humans make them a convenient experimental model. However, there is only a limited toolset available to measure behavior and organ function of these animals at medium or high-throughput. Herein, we describe an imaging-based platform to quantify body and autonomic movements of Xenopus tropicalis tadpoles of advanced developmental stages. Animals alternate periods of quiescence and locomotor movements and display buccal pumping for oxygen uptake from water and rhythmic cardiac movements. We imaged up to 24 animals in parallel and automatically tracked and quantified their movements by using image analysis software. Animal trajectories, moved distances, activity time, buccal pumping rates and heart beat rates were calculated and used to characterize the effects of test compounds. We evaluated the effects of propranolol and atropine, observing a dose-dependent bradycardia and tachycardia, respectively. This imaging and analysis platform is a simple, cost-effective high-throughput in vivo assay system for genetic, toxicological or pharmacological characterizations.