Functional analysis of the musculo‐skeletal system of the gill apparatus in Heptranchias perlo (Chondrichthyes: Hexanchidae)

Musculo‐skeletal morphology is an indispensable source for understanding functional adaptations. Analysis of morphology of the branchial apparatus of Hexanchiform sharks can provide insight into aspects of their respiration that are difficult to observe directly. In this study, I compare the structure of the musculo‐skeletal system of the gill apparatus of Heptranchias perlo and Squalus acanthias in respect to their adaptation for one of two respiratory mechanisms known in sharks, namely, the active two‐pump (oropharyngeal and parabranchial) ventilation and the ram‐jet ventilation. In both species, the oropharyngeal pump possesses two sets of muscles, one for compression and the other for expansion. The parabranchial pump only has constrictors. Expansion of this pump occurs only due to passive elastic recoil of the extrabranchial cartilages. In Squalus acanthias the parabranchial chambers are large and equipped by powerful superficial constrictors. These muscles and the outer walls of the parabranchial chambers are much reduced in Heptranchias perlo , and thus it likely cannot use this pump. However, this reduction allows for vertical elongation of outer gill slits which, along with greater number of gill pouches, likely decreases branchial resistance and, at the same time, increases the gill surface area, and can be regarded as an adaptation for ram ventilation at lower speeds.     

Voluntary and Involuntary Control of Breathing with Imposed Ventilation Parameters

To clarify the mechanisms of interaction between voluntary and involuntary control of respiratory movements in a waking human, respiratory patterns were studied during self-controlled artificial ventilation used in place of natural breathing. Seven subjects controlled both the duration of artificial inhalations and the flow rate of air at excess pressure, continuously adjusting their actions to obtain the sensation of comfortable breathing. At rest, pulmonary ventilation was higher during self-controlled artificial breathing than during natural breathing. This trend was also noted during exercise. A correlation was observed between the velocity of the movement that started air flow and the artificial ventilation volume (r = 0.91). During self-controlled artificial breathing, the subjects sometimes took natural breaths. Natural inhalations did not influence the beginning or end of an artificial inhalation. Information received from respiratory receptors was assumed to play a certain role in the self-control of artificial breathing.     

Prey capture in the pike-perch,Stizostedion lucioperca (teleostei,percidae): A structural and functional analysis

Summary The pike-perch,Stizostedion lucioperca, uses both suction and grasping during feeding. Type, size, and position of prey and predator determine the movement of catching. This is concluded from simultaneous motion analysis, electromyography, and the record of pressures inside the buccopharyngeal cavity during feeding. The EMG incorporates 24 muscles of the head, including the branchial basket and the anterior body musculature. When the pike-perch begins to feed acceleration and expansion of the head parts determine the negative buccopharyngeal pressure and therefore the suction force applied to different preys. Not the head muscles, but the epaxial and hypaxial body musculatures provide the main force for the rapid expansion of the head through movements of the neurocranium, pectoral girdle, and hyoid arch. Despite the lack of a true neck, the pike-perch is able to move its neurocranium in all directions to aim the suction force. The experiments revealed that ventral and lateral movements aid in the ingestion of a big prey after it has been grasped with the teeth. The head muscles are active as regulators of the opening movements and in the closing movements. Variable overlaps of ab- and adductor activity show that their contraction patterns are interdependent. Variations in the recorded pressures can be related largely to a series of EMGs showing different starting moments of adductor contraction. In this progressive series two patterns were distinguished, and their accompanying movements were compared and related to the type of prey. According to the feeding behavior and morphology, the pike-perch is classified as a rapacious predator. Comparison with some other voracious fishes shows that besides the total length of the lower jaw and the dentigerous area, the construction and dentition of the upper jaws and the anterior suspensorial and neurocranial parts are also important features of this ecological type. However it appears that the fishes selected for this comparison use suction rather than the teeth as the main means of catching the smaller, but commonly eaten prey. The teeth prevent escape after capture by sucking and they increase the maximum prey size that can be caught. In this group, the head ofStizostedion appears to be comparatively well adapted to sucking with grasping adaptations.     

Linking cranial morphology to prey capture kinematics in three cleaner wrasses: Labroides dimidiatus,Larabicus quadrilineatus,and Thalassoma lutescens

Cleaner fishes are well known for removing and consuming ectoparasites off other taxa. Observers have noted that cleaners continuously “pick” ectoparasites from the bodies of their respective client organisms, but little is known about the kinematics of cleaning. While a recent study described the jaw morphology of cleaners as having small jaw‐closing muscles and weak bite forces, it is unknown how these traits translate into jaw movements during feeding to capture and remove ectoparasites embedded in their clients. Here, we describe cranial morphology and kinematic patterns of feeding for three species of cleaner wrasses. Through high‐speed videography of cleaner fishes feeding in two experimental treatments, we document prey capture kinematic profiles for Labroides dimidiatus, Larabicus quadrilineatus, and Thalassoma lutescens. Our results indicate that cleaning in labrids may be associated with the ability to perform low‐displacement, fast jaw movements that allow for rapid and multiple gape cycles on individually targeted items. Finally, while the feeding kinematics of cleaners show notable similarities to those of “picker” cyprinodontiforms, we find key differences in the timing of events. In fact, cleaners generally seem to be able to capture prey twice as fast as cyprinodontiforms. We thus suggest that the kinematic patterns exhibited by cleaners are indicative of picking behavior, but that “pickers” may be more kinematically diverse than previously thought. J. Morphol. 276:1377–1391, 2015. © 2015 Wiley Periodicals, Inc.     

The fictively breathing tadpole brainstem preparation as a model for the development of respiratory pattern generation and central chemoreception

Spontaneous high-frequency, low-amplitude and low-frequency, high-amplitude efferent bursting patterns of cranial and spinal motor nerve activity in the in vitro brainstem preparation of the bullfrog tadpole Rana catesbeiana have been characterized as fictive gill and lung ventilation, respectively (Gdovin MJ, Torgerson CS, Remmers JE). Characterization of gill and lung ventilatory activity in cranial nerves in the spontaneously breathing tadpole Rana catesbeiana, FASEB J 1996;10(3):A642; Gdovin MJ, Torgerson CS, Remmers JE. Neurorespiratory pattern of gill and lung ventilation in the decerebrate spontaneously breathing tadpole, Respir Physiol 1998;113:135 146; Pack AI, Galante RJ, Walker RE, Kubin LK, Fishman AP. Comparative approach to neural control of respiration, In: Speck DF, Dekin MS, Revelette WR, Frazier DT, editors. Respiratory Control Central and Peripheral Mechanisms. Lexington: University of Kentucky Press, 1993:52-57). In addition, the ontogenetic dependence of central respiratory chemoreceptor stimulation on fictive gill and lung ventilation has been previously described (Torgerson CS, Gdovin MJ, Remmers JE. Fictive gill and lung ventilation in the pre- and post-metamorphic tadpole brainstem, J Neurophysiol 1998, in press). To investigate the neural substrates responsible for central respiratory rhythm generation of gill and lung ventilation in the developing tadpole, we recorded efferent activities of cranial nerve (CN) V, VII, and X and spinal nerve (SN) II during changes in superfusate PCO2 before and after multiple transection of the in vitro brainstem. The brainstem was transected between CN VIII and IX and the response to changes in PCO2 was recorded. A second transection was then made between the caudal margin of CN X and rostral to SN II. Preliminary data reveal that robust gill ventilation was recorded consistently only if the segment of brainstem included CN X, whereas the loci capable of eliciting fictive lung bursting patterns appeared to differ depending on developmental stage. These data demonstrate that the neural substrate required for fictive gill and lung ventilation exists in anatomically separate regions such that the gill central pattern generator (CPG) is located in the caudal medulla at the level of CN X throughout development, whereas the location of the lung CPG is located more rostrally at the level of CN VII in the post-metamorphic larva. Both in vivo and in vitro studies revealed two distinct neural bursting patterns associated with gill and lung ventilation. Sequential activation of CN V, VII, X were observed during gill ventilation of in vivo and fictive gill ventilation in vitro, whereas these nerve activities, along with SN II displayed more synchronous bursting patterns of activation during lung ventilation and fictive lung breaths.     

Lung ventilation in salamanders and the evolution of vertebrate air-breathing mechanisms

Functional analysis of lung ventilation in salamanders combined with historical analysis of respiratory pumps provides new perspectives on the evolution of breathing mechanisms in vertebrates. Lung ventilation in the aquatic salamander Necturus maculosus was examined by means of cineradiography, measurement of buccal and pleuroperitoneal cavity pressures, and electromyography of hypaxial musculature. In deoxygenated water Necturus periodically rises to the surface, opens its mouth, expands its buccal cavity to draw in fresh air, exhales air from the lungs, closes its mouth, and then compresses its buccal cavity and pumps air into the lungs. Thus Necturus produces only two buccal movements per breath: one expansion and one compression. Necturus shares the use of this two-stroke buccal pump with lungfishes, frogs and other salamanders. The ubiquitous use of this system by basal sarcopterygians is evidence that a two-stroke buccal pump is the primitive lung ventilation mechanism for sarcopterygian vertebrates. In contrast, basal actinopterygian fishes use a four-stroke buccal pump. In these fishes the buccal cavity expands to fill with expired air, compresses to expel the pulmonary air, expands to fill with fresh air, and then compresses for a second time to pump air into the lungs. Whether the sarcopterygian two-stroke buccal pump and the actinopterygian four-stroke buccal pump arose independently, whether both are derived from a single, primitive osteichthyian breathing mechanism, or whether one might be the primitive pattern and the other derived, cannot be determined. Although Necturus and lungfishes both use a two-stroke buccal pump, they differ in their expiration mechanics. Unlike a lungfish (Protopterus), Necturus exhales by contracting a portion of its hypaxial trunk musculature (the m. Iransversus abdominis) to increase pleuroperitoneal pressure. The occurrence of this same expiratory mechanism in amniotes is evidence that the use of hypaxial musculature for expiration, but not for inspiration, is a primitive tetrapod feature. From this observation we hypothesize that aspiration breathing may have evolved in two stages: initially, from pure buccal pumping to the use of trunk musculature for exhalation but not for inspiration (as in Necturus); and secondarily, to the use of trunk musculature for both exhalation and inhalation by costal aspiration (as in amniotes).     

Surface morphology and functions of pharyngeal structures in the larval lamprey Petromyzon marinus

To gain insight into the multiple functions of a complex biological structure, the morphology of the pharynx of the larva (ammocoete) of the lamprey Petromyzon marinus was investigated with scanning electron microscopy and histochemistry (PAS and Alcian blue). Features studied include the gills, the parabranchial chambers external to the gills, intrapharyngeal ciliary tracts, the ridged pharyngeal roof, the floor, and the intrapharyngeal taste buds. Significant findings are: (1) All (nonciliated) cells lining these structures are covered with microvilli or microridges. The pattern and packing density of these membrane features vary among different pharyngeal structures. The lumenar membranes of pharyngeal lining cells overlie a mucous prosecretion in the apical cytoplasm, suggesting that the microvilli/ridges on these membranes function to anchor mucus. (2) Patterns of microvilli/ridges on the gill respiratory lamellae differ among ammocoetes of different species. (3) Pharyngeal osmo-regulatory cells (“chloride cells”) could not be identified on the basis of the microvillus/ridge pattern. (4) Two types of ciliary tracts are present within the pharynx. One has tall (x = 13 μm) and densely packed cilia, whereas the other has shorter (x = 7 μm) and less densely packed ones. Because mucus covers both types of tracts their function appears to involve the transport of mucus. (5) Food particles were found on the lateral surfaces of the gill filaments and on the surfaces of the parabranchial chambers. It appears that goblet cells in the epithelia of these regions secrete mucus in which the particles are trapped.     

Whisking as a “voluntary” response: operant control of whisking parameters and effects of whisker denervation

The rat’s ability to vary its whisking “strategies” to meet the functional demands of a discriminative task suggests that whisking may be characterized as a “voluntary” behavior—an operant—and like other operants, should be modifiable by appropriate manipulations of response–reinforcer contingencies. To test this hypothesis we have used high-resolution, optoelectronic “real-time” recording procedures to monitor the movements of individual whiskers and reinforce specific movement parameters (amplitude, frequency). In one operant paradigm (N = 9) whisks with protractions above a specified amplitude were reinforced (Variable Interval 30?s) in the presence of a tone, but extinguished (EXT) in its absence. In a second paradigm (N = 3), rats were reinforced on two different VI schedules (VI-20s/VI-120s) signaled, respectively, by the presence or absence of the tone. Selective reinforcement of whisking movements maintained the behavior over many weeks of testing and brought it under stimulus and schedule control. Subjects in the first paradigm learned to increase responding in the presence of the tone and inhibit responding in its absence. In the second paradigm, subjects whisked at significantly different rates in the two stimulus conditions. Bilateral deafferentation of the whisker pad did not impair conditioned whisking or disrupt discrimination behavior. Our results confirm the hypothesis that rodent whisking has many of the properties of an operant response. The ability to bring whisking movement parameters under operant control should facilitate electrophysiological and lesion/behavioral studies of this widely used “model” sensorimotor system.     

Hypoxic cardiorespiratory reflexes in the facultative air-breathing fish jeju (Hoplerythrinus unitaeniatus): role of branchial O2 chemoreceptors

In one series of experiments, heart frequency (f _H), blood pressure (P _a), gill ventilation frequency (f _R ), ventilation amplitude (V _AMP) and total gill ventilation (V _TOT) were measured in intact jeju (Hoplerythrinus unitaeniatus) and jeju with progressive denervation of the branchial branches of cranial nerves IX (glossopharyngeal) and X (vagus) without access to air. When these fish were submitted to graded hypoxia (water PO₂ ~140, normoxia to 17 mmHg, severe hypoxia), they increased f _R , V _AMP, V _TOT and P _a and decreased f _H. In a second series of experiments, air-breathing frequency (f _RA), measured in fish with access to the surface, increased with graded hypoxia. In both series, bilateral denervation of all gill arches eliminated the responses to graded hypoxia. Based on the effects of internal (caudal vein, 150 μg NaCN in 0.2 mL saline) and external (buccal) injections of NaCN (500 μg NaCN in 1.0 mL water) on f _R , V _AMP, V _TOT, P _a and f _H we conclude that the O₂ receptors involved in eliciting changes in gill ventilation and associated cardiovascular responses are present on all gill arches and monitor the O₂ levels of both inspired water and blood perfusing the gills. We also conclude that air breathing arises solely from stimulation of branchial chemoreceptors and support the hypothesis that internal hypoxaemia is the primary drive to air breathing.     

Morphology of the gills of larval and parasitic adult sea lamprey,Petromyzon marinus L.

The general morphology of the gills is similar in larval (ammocoetes) and parasitic adult sea lampreys, Petromyzon marinus, despite different methods of ventilation necessitated by their feeding habits. The gill lamellae are supported by randomly-distributed pillar cells which enclose blood spaces and collagen columns. The distribution of these cells in lampreys is different from that of higher fishes and it may be inefficient for respiratory exchange. The presence of cytoplasmic microfilaments suggests that these cells have the ability to reduce the lamellar blood spaces through contraction. Marginal channels at the tips of the lamellae are lined only by endothelial cells. The thickness of the water-blood pathway in lampreys falls within the range described for higher fishes, with the most efficient gas exchange likely occurring at the lamellar tips where only a single layer of epithelial cells is present. The abrupt increase in height of the epithelium near the lamellar bases in adults, compared to the gradual transition in height along the lamellae in ammocoetes, is perhaps reflective of higher oxygen requirements during the parasitic stage. The consistent appearance of wide, lateral intercellular spaces within the respiratory epithelium of lampreys indicates possible involvement of these spaces in transport. Mucous secretion appears to be an important function of the superficial platelet cells in ammocoetes. “Mitochondria-rich” and “mitochondria-poor” superficial cells are observed in both ammocoetes and adults, with the mitochondria-rich cells more prevalent toward the lamellar bases. The possibility that at least some of these cells may be involved in absorption is discussed. Mitochondria-rich cells in the interlamellar region are morphologically different in ammocoetes and adults but all possess an abundance of smooth endoplasmic reticulum and hence resemble “chloride cells” of higher fishes. The similarity of these cells in the parasitic adult lamprey to chloride cells of marine fishes may reflect the potential of the adult lamprey to osmoregulate in salt water. A scarcity of these cells in ammocoetes and their resemblance to chloride cells in freshwater fishes may reflect the restriction of larval lampreys to a freshwater habitat.     

Effects of expiratory loading on respiration in humans

We examined the effects of expiratory resistive loads of 10 and 18 cmH2O.l-1.s in healthy subjects on ventilation and occlusion pressure responses to CO2, respiratory muscle electromyogram, pattern of breathing, and thoracoabdominal movements. In addition, we compared ventilation and occlusion pressure responses to CO2 breathing elicited by breathing through an inspiratory resistive load of 10 cmH2O.l-1.s to those produced by an expiratory load of similar magnitude. Both inspiratory and expiratory loads decreased ventilatory responses to CO2 and increased the tidal volume achieved at any given level of ventilation. Depression of ventilatory responses to Co2 was greater with the larger than with the smaller expiratory load, but the decrease was in proportion to the difference in the severity of the loads. Occlusion pressure responses were increased significantly by the inspiratory resistive load but not by the smaller expiratory load. However, occlusion pressure responses to CO2 were significantly larger with the greater expiratory load than control. Increase in occlusion pressure observed could not be explained by changes in functional residual capacity or chemical drive. The larger expiratory load also produced significant increases in electrical activity measured during both inspiration and expiration. These results suggest that sufficiently severe impediments to breathing, even when they are exclusively expiratory, can enhance inspiratory muscle activity in conscious humans.     

Branchial mechanoreceptor activity during spontaneous ventilation in channel catfish

Extracellular afferent neural activity was recorded in vivo from cranial nerve IX (glossopharyngeal) from mechanoreceptors in the first gill arch of anesthetized, spontaneously breathing channel catfish (Ictalurus punctatus). Single unit and paucifiber recordings show that both phasic and tonic receptors were active during normal ventilation. Phasic receptors were characterized as having a burst of activity during some phase of the ventilatory cycle. Most of these occurred during peak adduction or peak abduction. Phasic receptors were not active during spontaneous apnic periods. Tonic receptors were always active, even during apneas, firing frequency was modulated by breathing movements with peak activity occurring during adduction. Flow-sensitive mechanoreceptors were identified in anesthetized, paralyzed catfish. These receptors decreased activity when the ventilatory water flow was stopped. Hypercapnia (5% CO(2) in air) stimulated ventilatory rate and amplitude but had no effect on mechanoreceptor activity. The discharge characteristics of branchial mechanoreceptors indicate that they could be involved in the timing and coordination of ventilatory movements and maintenance of the 'gill curtain' to minimize ventilatory dead space. Unlike ventilatory mechanoreceptors in the air breathing organs of gar and lungs of lungfish and tetrapods, branchial mechanoreceptors were insensitive to hypercapnia.     

On the respiratory organs of amphipnous cuchia (Ham Buch)

The respiratory organs of Amphipnous cuchia comprise a pair of aicsacs, vestigial gill filaments borne on second gill arch and vascular folds of the third gill arch. The volume of each air-sac, its surface area and its reltionship with the body weight of the fish have been determined. The air-sac is lined by a respiratory mucosa which is composed of vascular and non-vascular areas. Each vascular area, called here the ‘respiratory islet,’ studded with hundreds of vascular rosettes, which are formed of collagenous material and supported by endothelial cells. Pilaster cells are absent. The ‘islets’ are covered over by a single layer of squamous type of epithelial cells. The non-vascular areas (lanes') are the stratified part of the respiratory epithelium and contain a large number of mucous glands which secrete mainly acid mucopolysaccharides. The vascularisation of the gills have been studied by India ink injection methods. The secondary gill lamellae are absent, their place being taken up by coiled vascular loops. A quantitative estimation of haemoglobin in blood of ‘cuchia’ and other air- and water-breathing fishes have been made by colorimetric method and the results have been discussed in relation to their habit and habitats. The cranial muscles which are involved in respiration of ‘cuchia’ and the mechanics of muscle action in breathing have been described.     

Edgeworth's legacy of cranial muscle development with an analysis of muscles in the ventral gill arch region of batoid fishes (Chondrichthyes: Batoidea).

A series of studies by Edgeworth demonstrated that cranial muscles of gnathostome fishes are embryologically of somitic origin, originating from the mandibular, hyoid, branchial, epibranchial, and hypobranchial muscle plates. Recent experimental studies using quail-chick chimeras support Edgeworth's view on the developmental origin of cranial muscles. One of his findings, the existence of the premyogenic condensation constrictor dorsalis in teleost fishes, has also been confirmed by molecular developmental studies. Therefore, developmental mechanisms for patterning of cranial muscles, as described and implicated by Edgeworth, may serve as structural entities or regulatory phenomena responsible for developmental and evolutionary changes. With Edgeworth's and other studies as background, muscles in the ventral gill arch region of batoid fishes are analyzed and compared with those of other gnathostome fishes. The spiracularis is regarded as homologous at least within batoid fishes, but its status within elasmobranchs remains unclear; developmental modifications of the spiracularis proper are evident in some batoid fishes and in several shark groups. The peculiar ventral extension of the spiracularis in electric rays and some stingrays may represent convergence, probably facilitating ventilation and/or feeding in both groups. The evolutionary origin of the "internus" and "externus" remains uncertain, despite the fact that a variety of forms of the constrictor superficiales ventrales in batoid fishes indicates an actual medio-ventral extension of the "externus." The intermandibularis is probably present only in electric rays. The "X" muscle occurs only in electric rays and is considered to be Edgeworth's intermandibularis profundus. Its association with the adductor mandibular complex in narkinidid and narcinidid electric rays may relate to its functional role in lower jaw movement. Contrary to common belief, in most batoid fishes as well as some sharks, muscles that originate from the branchial muscle plate and extend medially in the ventral gill arches do exist: the medial extension of the interbranchiales in most batoid fishes and some sharks and the "Y" muscle in the pelagic stingrays Myliobatos and Rhinoptera. The latter is another example of the medial extension of the "internus." Whether the interbranchiales and "Y" muscle are homologous within elasmobranchs and whether homologous with the obliques ventrales and/or transversi ventrales of osteichthyan fishes await further research. Four hypobranchial muscles are recognized in batoid fishes: the coracomandibularis, coracohyoideus, coracoarcualis, and coracohyomandibularis. The coracohyoideus is discrete from the coracoarcualis; its complete structural separation from the latter occurs in several groups of batoid fishes.(ABSTRACT TRUNCATED AT 400 WORDS)     

DELIMITING SPAWNING AREAS OF WEAKFISH CYNOSCION REGALIS (FAMILY SCIAENIDAE) IN PAMLICO SOUND,NORTH CAROLINA USING PASSIVE HYDROACOUSTIC SURVEYS

ABSTRACT

Exact locations of spawning areas used by marine fishes are needed to design marine reserves and estimate spawning stocks. The location of spawning areas of soniferous fishes such as weakfish Cynoscion regalis can be determined by means of passive hydroacoustic surveys. We conducted nocturnal hydrophone surveys at 12 locations in Pamlico Sound in May of 1996 and 1997. Digital audio tapes were made of weakfish “purring” sounds, the tapes were analyzed spectrographically and compared with ichthyoplankton surveys taken at the same stations and times. All weakfish “purring” sounds were recorded at stations near inlets. Maximum sound pressure levels recorded after sunset were 127 dB (re 1 (μPa) for individual weakfish, but reached a maximum of 147 dB when weakfish and other fish were producing sounds simultaneously. The maximum distance that an individual weakfish “purr” can be detected above the background sound, assuming a cylindrical spreading model, is approximately 50 m. There was a strong association (r = 0.78) between the log₁₀— transformed abundance of early-stage sciaenid-type eggs and maximum sound pressure levels, with the greatest numbers occurring at the inlet stations. These results suggest that passive hydroacoustic surveys can be used to delimit spawning areas for conservation and management purposes.     

Papyrus swamps, hypoxia, and faunal diversification: variation among populations of Barbus neumayeri

To test whether patches of papyrus swamp contribute to diversification of populations of non-air-breathing fishes, the gill morphology of Barbus neumayeri was compared between a papyrus swamp and several tributaries which differed in oxygen regime. Total gill filament length differed among sites and was negatively related to dissolved oxygen availability, supporting strong selection pressure for low-oxygen tolerance in the swamp interior. Among recaptures of marked B. neumayeri over a 4·5-year period among the focal swamp and connected stream and river sites, 93% of fish were recovered at the site of capture. Some of the individuals that moved crossed physicochemical gradients and traversed long distances within the swamp/stream system. This movement rate would theoretically be sufficient to homogenize gene frequencies among populations. However, randomly amplified polymorphic DNA (RAPD) markers indicated significant genetic differentiation among sites and no relationship between genetic differences and geographical distances among sites suggesting habitat-specific selection pressures on dispersers, rather than insufficient dispersal.     

Function of intracoelomic septa in lung ventilation of amniotes: lessons from lizards

Aspiration breathing is the dominant mechanism of lung inflation among extant amniotes. However, aspiration has two fundamental problems associated with it: paradoxical visceral translation and partial lung collapse. These can constrain the inspiratory tidal volume, reduce the effective lung ventilation, and ultimately curtail the aerobic capacity of an animal. Separation of the pleural and peritoneal cavities by an intracoelomic septum can restrict the cranial shift of abdominal viscera and provide structural support to the caudal lung surface. A muscular septum, such as the diaphragm of mammals or the diaphragmaticus of crocodilians, can exert active control over visceral translation and the degree of lung inflation. To a lesser degree, a nonmuscular septum can also function as a passive barrier when stretched taut by rib rotation. Studies of the posthepatic septum in teiid lizards and the postpulmonary septum in varanid lizards underscore the importance of nonmuscular septa in aspiration. These septa provide plausible functional models that help us infer the evolution of mammalian and avian lung ventilatory systems, respectively.     

THE CONTRIBUTION OF GENE MOVEMENT TO THE “TWO RULES OF SPECIATION”

The two “rules of speciation”—the Large X‐effect and Haldane's rule—hold throughout the animal kingdom, but the underlying genetic mechanisms that cause them are still unclear. Two predominant explanations—the “dominance theory” and faster male evolution—both have some empirical support, suggesting that the genetic basis of these rules is likely multifarious. We revisit one historical explanation for these rules, based on dysfunctional genetic interactions involving genes recently moved between chromosomes. We suggest that gene movement specifically off or onto the X chromosome is another mechanism that could contribute to the two rules, especially as X chromosome movements can be subject to unique sex‐specific and sex chromosome specific consequences in hybrids. Our hypothesis is supported by patterns emerging from comparative genomic data, including a strong bias in interchromosomal gene movements involving the X and an overrepresentation of male reproductive functions among chromosomally relocated genes. In addition, our model indicates that the contribution of gene movement to the two rules in any specific group will depend upon key developmental and reproductive parameters that are taxon specific. We provide several testable predictions that can be used to assess the importance of gene movement as a contributor to these rules in the future.     

The future distribution of river fish: The complex interplay of climate and land use changes,species dispersal and movement barriers

The future distribution of river fishes will be jointly affected by climate and land use changes forcing species to move in space. However, little is known whether fish species will be able to keep pace with predicted climate and land use‐driven habitat shifts, in particular in fragmented river networks. In this study, we coupled species distribution models (stepwise boosted regression trees) of 17 fish species with species‐specific models of their dispersal (fish dispersal model FIDIMO) in the European River Elbe catchment. We quantified (i) the extent and direction (up‐ vs. downstream) of predicted habitat shifts under coupled “moderate” and “severe” climate and land use change scenarios for 2050, and (ii) the dispersal abilities of fishes to track predicted habitat shifts while explicitly considering movement barriers (e.g., weirs, dams). Our results revealed median net losses of suitable habitats of 24 and 94 river kilometers per species for the moderate and severe future scenarios, respectively. Predicted habitat gains and losses and the direction of habitat shifts were highly variable among species. Habitat gains were negatively related to fish body size, i.e., suitable habitats were projected to expand for smaller‐bodied fishes and to contract for larger‐bodied fishes. Moreover, habitats of lowland fish species were predicted to shift downstream, whereas those of headwater species showed upstream shifts. The dispersal model indicated that suitable habitats are likely to shift faster than species might disperse. In particular, smaller‐bodied fish (<200 mm) seem most vulnerable and least able to track future environmental change as their habitat shifted most and they are typically weaker dispersers. Furthermore, fishes and particularly larger‐bodied species might substantially be restricted by movement barriers to respond to predicted climate and land use changes, while smaller‐bodied species are rather restricted by their specific dispersal ability.     

Are circulating catecholamines involved in the control of breathing by fishes?

Summary In this review, we have provided evidence that elevated levels of circulating catecholamines are not a significant factor in the control of ventilation in fishes, but rather that this critical physiological function is controlled primarily by the external and/or internal respiratory status. This view, which opposes the more traditional consensus (review: Randall and Taylor, 1991), is based upon numerous experimental observations, theoretical considerations, and a re-evaluation of previous studies.First, circulating catecholamine levels become elevated in fish only as a final survival strategy during severe stress, whereas hyperventilatory responses begin with very slight alterations in blood/water chemistry. Thus, except during extreme stress, plasma catecholamine levels and gill ventilation volume (V _w) do not co-vary. Second, with the notable exception of the European eel (Anguilla anguilla; Peyraud-Waitzenegger, 1979), experimental elevations of circulating catecholamine levels by injection/infusion of adrenalin or noradrenalin either do not alter ventilation in a physiologically significant manner or may occasionally even depress ventilation. Further, the sudden release of endogenous catecholamines during severe stress does not appear to modify the pre-existing hyperventilatory response. Third, although treatment of fish with selective adrenoceptor antagonists has yielded conflicting results to both support and reject a role for circulating catecholamines in the control of ventilation, it is nonetheless clear that such as experimental protocol cannot adequately differentiate between central and peripheral adrenergic phenomena.We suggest that there is no basis to support a role for circulating catecholamines in the regulation of breathing in fishes, and contend that discrepancies in the literature reflect the inherent difficulties associated with separating neural and humoral adrenergic phenomena.