The Morphology and Evolution of the Ear in Actinopterygian Fishes

SYNOPSIS. In this paper we consider various aspects of the anatomyand ultrastructure of the actinopterygian ear and make a numberof suggestions on the possible adaptive significance of thestructural specializations. The focus of the arguments is basedupon the substantial inter-specific variation in teleost auditorysystems as measured anatomically, behaviorally, and physiologically.It is potentially of considerable significance that the majorpoints of inter-specific variation in the teleost ear are associatedwith the gross morphology and ultrastructure of the otolithicorgan most often implicated in sound detection, the sacculus.Analysis of patterns of sacculus ultrastructure has led to theconclusion that there are, in effect, only about five differentsaccular ultrastructural patterns but that these patterns arebroadly found throughout the teleost fishes. Based upon patternsof inter-specific variation in the sacculus and in other aspectsof the ear and more peripheral auditory structures (e.g., swimbladder),it is argued that adaptations encountered in the teleost auditorysystem cannot be used as reliable taxonomic indicators amongfishes. Rather, it is proposed that the teleost auditory systemis quite maleable in the evolutionary sense, and that interspecificsimilarities in many features of the auditory system reflectconvergent evoluuon, rather than phylogenetic affinities. Theactual selective pressures operating in the evoluuon of thefish auditory system are still essentially unknown. In addition,we cannot be certain that similar ear patterns in differentspecies reflect convergent evolution (or common ancestry), orthat conversely, different ear patterns among species reflectdifferences in auditory function.     

Locomotor Patterns in the Evolution of Actinopterygian Fishes

SYNOPSIS. Locomotor adaptations in actinopterygian fishes aredescribed for (a) caudal propulsion, used in cruising and sprintswimming, acceleration, and fast turns and (b) median and pairedfin propulsion used for slow swimming and in precise maneuver.Caudal swimming is subdivided into steady (time independent)and unsteady (time dependent acceleration and turning) locomotion. High power caudal propulsion is the major theme in actinopterygianswimming morphology because of its role in predator evasionand food capture. Non-caudal slow swimming appears to be secondaryand is not exploited before the Acanthopterygii. Optimal morphological requirements for unsteady swimming are(a) large caudal fin and general body area, (b) deep caudalpeduncle, often enhanced by posterior dorsal and anal fins,(c) an anterior stabilizing body mass andor added mass, (d)flexible body and (e) large ratio of muscle mass to body mass.Optimal morphological requirements for steady swimming are (a)high aspect ratio caudal fin, (b) narrow caudal peduncle, (c)small total caudal area, (d) anterior stabilizing body massand added mass, and (e) a stiff body. Small changes in morphologycan have large effects on performance. Exclusive morphological requirements for steady versus unsteadyswimming are partially overcome using collapsible fins, butcompromises remain necessary. Morphologies favoring unsteadyperformance are a recurring theme in actinopterygian evolution.Successive radiations at chondrostean, halecostome and teleosteanlevels are associated with modifications in the axial and caudalskeleton. Strength of ossified structures probably limited maximum propulsionforces early in actinopterygian evolution, so that specializationsfor fast cruising (carangiform and thunmform modes) followedstructural advances especially in the caudal skeleton. No suchlimits apply to eel-like forms which consequently recur in successiveactinopterygian radiations. Slow swimming using mainly non-caudal propulsion probably firstoccurred among neopterygians in association with reduced andneutral buoyancy. Slow swimming adaptations can add to and extendthe scope of caudal swimming, but specialization is associatedwith reduced caudal swimming performance. Marked exploitationof slow swimming opportunities does not occur prior to the anterodorsallocation of pectoral and pelvic girdles and the vertical rotationof the base of the pectoral fin, as found in the Acanthopterygii.     

Symposium Summary: Evolutionary Patterns in Actinopterygian Fishes

SYNOPSIS. The actinopterygian fishes are an exemplary cladefor the study of structural and functional evolutionary patterns.With over half of all vertebrate species, ray-finned fisheshave diversified into a wide variety of habitats, and considerableprogress has been made over the last fifteen years in understandingthe genealogical relationships of actinopterygians. This symposiumhas contributed to our understanding of phylogenetic patternsin actinopterygians and to knowledge of the major structuraland functional patterns in locomotor, auditory, trophic, andneural systems. A number of key areas for future research havebeen identified. (1) The relationships of "palaeonisciform"fishes, (2) the study of trends in feeding and locomotor systemswithin a phylogenetic context, (3) the identification of primitivepatterns of pharyngeal jaw movement and steady and unsteadylocomotor patterns in actinopterygians, (4) the homologies,identification, and functional significance of neural pathwaysin the telencephalon, and (5) the comparative study of form-functionrelations in the auditory system. The study of teleost fishbiology has proceeded at the expense of data on primitive actinopterygians(e.g., Polypterus, Polyodon, Aapenser, Lepisosteus, Amia) whichare especially important in the analysis of structural and functionalpatterns in ray-finned fishes.     

Patterns of Evolution in the Feeding Mechanism of Actinopterygian Fishes

SYNOPSIS. Structural and functional patterns in the evolutionof the actinopterygian feeding mechanism are discussed in thecontext of the major monophyletic lineages of ray-finned fishes.A tripartite adductor mandibulae contained in a maxillary-palatoquadratechamber and a single mechanism of mandibular depression mediatedby the obliquus inferioris, sternohyoideus, and hyoid apparatusare primitive features of the Actinopterygii. Halecostome fishesare characterized by having an additional mechanism of mandibulardepression, the levator operculi—opercular series coupling,and a maxilla which swings anteriorly during prey capture. Theseinnovations provide the basis for feeding by inertial suctionwhich is the dominant mode of prey capture throughout the halecostomeradiation. A remarkably consistent kinematic profile occursin all suction-feeding halecostomes. Teleost fishes possessa number of specializations in the front jaws including a geniohyoideusmuscle, loss of the primitive suborbital adductor component,and a mobile premaxilla. Structural innovations in teleost pharyngealjaws include fusion of the dermal tooth plates with endoskeletalgill arch elements, the occurrence of a pharyngeal retractormuscle, and a shift in the origin of the pharyngohyoideus. Thesespecializations relate to increased functional versatility ofthe pharyngeal jaw apparatus as demonstrated by an electromyographicstudy of pharyngeal muscle activity in Esox and Ambloplites.The major feature of the evolution of the actinopterygian feedingmechanism is the increase in structural complexity in both thepharyngeal and front jaws. Structural diversification is a functionof the number of independent biomechanical pathways governingmovement.     

Microstructure and Growth of the Dermal Skeleton in Fossil Actinopterygian Fishes: Birgeria and Scanilepis

The dermal bones of Birgeria and Scanilepis contain numerous odontodes of consecutive generations, each consisting of dentine and a single ganoin layer; superimposition of series of ganoin layers, generally encountered in the scales of the palaeonisciforms. does not occur in any of these bones. In Birgeria , some odontodes near to the dentition resemble jaw-teeth proper in possessing an apical portion of acrodin; furthermore, nothing indicates the existence here of nerve-sac groups like those of sturgeons. The histology of the dermal skeleton in Scanilepis does not support the assumption that this form is more closely related to Polypterus than other palaeonisciforms. Remarks are given on the structure of acrodin and ganoin as revealed by SEM study.     

Microstructure and Growth of the Dermal Skeleton in Fossil Actinopterygian Fishes: Boreosomus, Plegmolepis and Gyrolepis

The odontodes of some of the palatal dermal bones in Boreosomus piveteaui Nielsen tend to form odontocomplexes, e.g. symmetrical areal ones where some degree of superimposition may occur between ganoin layers belonging to the component odontodes, and asymmetrical areal ones where this is quite insignificant. In the areal odontocomplexes of the dermal bones in Plegmolepis sp., the degree of overlap between the corresponding layers is somewhat more pronounced. Finally, in the areal odontocomplexes of the dermal bones in Gyrolepis cf. albertii Agassiz, we have a more advanced stage of phyletic specialization where each of the ganoin layers of the component odontodes lies directly superimposed on the preceding one throughout the extent of the latter. At the same time, the effect of phyletic dentine reduction is clearly noticeable here by the development of extra ganoin layers no more retaining their original connections with that hard tissue (also developed in the scales of Plegmolepis sp.). Remarks are i.a. given on the characters by which Acropholis and Plegmolepis are said to be distinguishable from each other.     

Prey Capture in Actinopterygian Fishes: A Review of Suction Feeding Motor Patterns with New Evidence from an Elopomorph Fish, Megalops atlanticus

Suction feeding is recognized as the dominant mode of aquaticprey capture in fishes. While much work has been done identifyingmotor pattern variations of this behavior among diverse groupsof actinopterygian fishes, many ray-finned groups are stillnot represented. Further, the substantial amount of inherentvariation in electromyography makes much of the pioneering workof suction feeding motor patterns in several basal groups insufficientfor evolutionary comparisons. Robust evolutionary comparisonshave identified conserved qualitative traits in the order ofmuscle activation during suction feeding (jaw opening > buccalcavity expansion > jaw closing). However, quantitative traitsof suction motor patterns (i.e., burst durations and relativeonset times) have changed over evolutionary time among actinopterygianfishes. Finally, new motor pattern evidence is presented froma previously neglected group, the Elopomorpha. The results suggestthat future investigations of the muscles influencing lateralexpansion of the mouth cavity and head anatomy may provide valuablenew insights into the evolution of suction feeding motor patternsin ray-finned fishes. In addition, the evidence illustratesthe value of comprehensive EMG surveys of cranial muscle activitiesduring suction feeding behavior.     

Morphology of the Mechanosensory Lateral Line System in Elasmobranch Fishes: Ecological and Behavioral Considerations

The relationship between morphology of the mechanosensory lateral line system and behavior is essentially unknown in elasmobranch fishes. Gross anatomy and spatial distribution of different peripheral lateral line components were examined in several batoids (Raja eglanteria, Narcine brasiliensis, Gymnura micrura, and Dasyatis sabina) and a bonnethead shark, Sphyrna tiburo, and are interpreted to infer possible behavioral functions for superficial neuromasts, canals, and vesicles of Savi in these species. Narcine brasiliensis has canals on the dorsal surface with 1 pore per tubule branch, lacks a ventral canal system, and has 8–10 vesicles of Savi in bilateral rows on the dorsal rostrum and numerous vesicles ( = 65 ± 6 SD per side) on the ventral rostrum. Raja eglanteria has superficial neuromasts in bilateral rows along the dorsal body midline and tail, a pair anterior to each endolymphatic pore, and a row of 5–6 between the infraorbital canal and eye. Raja eglanteria also has dorsal canals with 1 pore per tubule branch, pored and non-pored canals on the ventral surface, and lacks a ventral subpleural loop. Gymnura micrura has a pored dorsal canal system with extensive branch patterns, a pored ventral hyomandibular canal, and non-pored canal sections around the mouth. Dasyatis sabina has more canal pores on the dorsal body surface, but more canal neuromasts and greater diameter canals on the ventral surface. Sphyrna tiburo has primarily pored canals on both the dorsal and ventral surfaces of the head, as well as the posterior lateral line canal along the lateral body surface. Based upon these morphological data, pored canals on the dorsal body and tail of elasmobranchs are best positioned to detect water movements across the body surface generated by currents, predators, conspecifics, or distortions in the animal's flow field while swimming. In addition, pored canals on the ventral surface likely also detect water movements generated by prey. Superficial neuromasts are protected from stimulation caused by forward swimming motion by their position at the base of papillar grooves, and may detect water flow produced by currents, prey, predators, or conspecifics. Ventral non-pored canals and vesicles of Savi, which are found in benthic batoids, likely function as tactile or vibration receptors that encode displacements of the skin surface caused by prey, the substrate, or conspecifics. This mechanotactile mechanism is supported by the presence of compliant canal walls, neuromasts that are enclosed in wide diameter canals, and the presence of hair cells in neuromasts that are polarized both parallel to and nearly perpendicular to the canal axis in D. sabina. The mechanotactile, schooling, and mechanosensory parallel processing hypotheses are proposed as future directions to address the relationships between morphology and physiology of the mechanosensory lateral line system and behavior in elasmobranch fishes.     

Functional Morphology of Aquatic Flight in Fishes: Kinematics, Electromyography, and Mechanical Modeling of Labriform Locomotion

Labriform locomotion is the primary swimming mode for many fishesthat use the pectoral fins to generate thrust across a broadrange of speeds. A review of the literature on hydrodynamics,kinematics, and morphology of pectoral fin mechanisms in fishesreveals that we lack several kinds of morphological and kinematicdata that are critical for understanding thrust generation inthis mode, particularly at higher velocities. Several needsinclude detailed three-dimensional kinematic data on speciesthat are pectoral fin swimmers across a broad range of speeds,data on the motor patterns of pectoral fin muscles, and thedevelopment of a mechanical model of pectoral fin functionalmorphology. New data are presented here on pectoral fin locomotionin Gomphosus varius, a labrid fish that uses the pectoral finsat speeds of 1 –6 total body lengths per second. Three-dimensionalkinematic data for the pectoral fins of G. varius show thata typical "drag-based" mechanism is not used in this species.Instead, the thrust mechanics of this fish are dominated bylift forces and acceleration reaction forces. The fin is twistedlike a propeller during the fin stroke, so that angles of attackare variable along the fin length. Electromyographic data onsix fin muscles indicate the sequence of muscle activity thatproduces antagonistic fin abduction and adduction and controlsthe leading edge of the fin. EMG activity in abductors and adductorsis synchronous with the start of abduction and adduction, respectively,so that muscle mechanics actuate the fin with positive work.A mechanical model of the pectoral fin is proposed in whichfin morphometrics and computer simulations allow predictionsof fin kinematics in three dimensions. The transmission of forceand motion to the leading edge of the fin depends on the mechanicaladvantage of fin ray levers. An integrative program of researchis suggested that will synthesize data on morphology, physiology,kinematics, and hydrodynamics to understand the mechanics ofpectoral fin swimming.     

Interrelationships of yuccas and yucca moths

Purposeful pollination of yucca by females of a moth that produces larvae that feed on some of the seeds is a classic example of plant-animal mutualism. Recent research has focused on the complex interspecific nature of this association. Pollinators are members of two genera with different oviposition and larval biologies. There appear to be several sibling species among populations of the pollinator that were formerly considered to be a single widespread generalist, and these may include sympatric nonpollinator 'cheaters'. Bogus yucca moths, members of a third genus, which neither transport pollen nor feed in the seed but depend upon the inflorescences, are niche specific and often host-species specific and include one leaf-mining species. Their larvae can spend many years in diapause before synchronized development.     

Morphology of the eye and visual acuities in the settlement-intervals of some Coral Reef Fishes (Labridae, Scaridae)

The morphology of the retina and photoreceptors of settlement-interval larvae and early juveniles and some adults of 12 species of Caribbean labrids and scarids were examined using histological techniques. The retinal structure is described in these species and life intervals. Larvae have a pure cone retina and unorganized mosaic and organization into a square mosaic pattern occurs during metamorphosis. Early post-settlement juveniles have an organized mosaic with structures that may enable them to detect polarized and UV light. Visual acuities were calculated for all species and life intervals and acuities ranged between 86.6–29.4min of arc in the settlement-intervals and 16–1.8min of arc in the adults. The visual abilities of the settlement-interval fishes and the possibility of the use of vision during settlement are discussed.     

The Interrelationships of the Gastrotricha Using Nuclear Small rRNA Subunit Sequence Data, with an Interpretation Based on Morphology

Gastrotrichs are meiobenthic invertebrates of obscure origin and unclear phylogenetic alliances. Uncertainties also plague the intra-group relationship with major contrasts between the evolutionary scenarios inferred from morphology or molecules. In this study we analysed partial sequences of the 18S rDNA gene of 18 taxa (14 new and 4 published) to test morphological estimates of gastrotrich phylogeny and to verify whether controversial interrelationships from previous molecular data are due to poor sampling. Data were analysed using both maximum parsimony and maximum likelihood. MP topology was then forced to reflect published morphological estimates and the most parsimonious solutions from each constraint analysis was statistically compared against the unconstrained solution. MP analysis yielded a single tree with few nodes well supported by bootstrap resampling. These included the monophyly of the Chaetonotidae and the internal relationships of the members of this family, with Aspidiophorus appearing as the most basal member. The monophyly of the Turbanellidae was also well supported with some suggestion that its sister group might be Mesodasys. Lepidodasyidae was found to be an unnatural taxon with Lepidodasys forming a separated clade but unrelated also to the Thaumastodermatidae. With the exception of genera Lepidodasys and Neodasys, the Macrodasyida appeared to be resolved separately from the Chaetonotida, and Dactylopodola was resolved as the most basal macrodasyid. ML analysis yielded a tree not too dissimilar from MP, although Dactylopodola and Xenodasys were resolved as a clade. Statistics indicate that the output from our MP analysis is compatible with the classical view placing representatives of the two orders within two distinct evolutionary lines. Most of the constrained solutions, except the shortest, corroborate the monophyly of the two orders, whereas all five constrained solutions support also the notion that sees Neodasys as an early divergent clade along the Chaetonotida branch. Thus, results are generally compatible with the hypothesised evolutionary scenario based on morphological data, but are in contrast with previous findings from molecules. Future research should consider using the complete SSU rDNA gene sequence in their analysis and additional genes for deeper resolution.     

Features of the Changes in External Morphology and Axial Skeleton in Juvenile Salmonid Fishes (Salmonidae) Associated with Smoltification

Journal of Ichthyology - Changes in external morphological characters and relative lengths of vertebral centra from different regions of the vertebral column are analyzed during smoltification in...     

Adaptations of Cave Fishes with some Comparisons to Deep-sea Fishes

I provide my retrospective and prospective views on adaptations of cave fishes. I emphasize the history of my insights into cave adaptation from 45 years of research using surface, cave-spring, and cave species of amblyopsid fishes. My approach has been to use natural experiments and to always consider multiple hypotheses. To clarify evolutionary adaptations, I show the importance of a broad comparative approach which includes studies of morphology, metabolic physiology, foraging behavior, life history, and ecology. And I show that the most important agents of selection, of darkness and attendant low food supply, are best understood in the context of rigor, variability, and predictability. I also present my insights from what I consider the most insightful contributions on deep-sea fishes. The contributions are those of Marshall in studies of morphology in relation to energy economy of pelagic and benthic species, Childress in studies of physiological and biochemical adaptations with depth for pelagic species, and Koslow in studies on population biology and life history of bathybenthic and benthic sea-mount species. Compared to caves, I suggest that the extremes of metabolic and life history adaptations of deep-sea fish are explained by a longer evolutionary history and a much greater habitat range, food supply, and predation risk. Finally, I take a retrospective view of what we have learned about cave fishes. I discuss possible evolutionary mechanisms that can explain the trends with increasing cave adaptation in amblyopsid fishes, especially progenesis and the pleiotropic effects of the stress resistance syndrome. Finally, based on insights from deep-sea fishes, and emerging new techniques, I suggest what cave fish biologists should do in the future.     

脂鲤目鱼类和"食人鲳"

“食人鲳”是脂鲤目锯鲑脂鲤科锯鲑脂鲤属鱼类的俗称,这类鱼原产南美洲亚马逊河流域,目前已经作为观赏鱼类被引入到包括中国在内的世界上很多国家和地区,而我们对“食人鲳”所属的脂鲤目鱼类还不甚了解。简要地介绍了有关该类群鱼类的分类学及其他一些基本情况,并以“食人鲳”作为代表动物,就锯鲑脂鲤属鱼类的系统学、形态学、生物学信息等进行了较为详细地讨论和介绍。     

Interrelationships between polyamines and nucleic acids

Summary The distribution of radioactivity from ³H-putrescine was studied in intact and degenerated sciatic nerves, and spinal ganglia of rats by means of high resolution autoradiography. During the first three days after the administration of the labeled putrescine, the main proportion of radioactive material in the nerves was represented by spermidine and putrescine. Both, in intact and degenerating nerves, developed silver grains were deposited in all cellular components of the nervous tissue, the myelin sheath being markedly tagged. Perineural tissue was also labeled considerably, however, there was no significant amount of label in the extracellular space and in the collagen fibrils. The possible physiological significance of putrescine and spermidine in myelin and in other cellular components of nerves is discussed.Herrn Prof. Dr. W. Krücke zum 60. Geburtstag gewidmet.     

Interrelationships of oxygen consumption and insecticide sensitivity

The circadian rhythms of oxygen consumption and insecticide sensitivity (to dichlorvos, a rapid-acting organophosphate) in adult confused flour beetles (Tribolium confusum du Val) were determined using a LD 12:12 lighting regimen and other standardized conditions. Analysis included fitting a 24 h cosine curve to the data to estimate rhythm characteristics. Relationships between rhythms in oxygen consumption and insecticide sensitivity were evaluated on the basis of each rhythm's acrophase (timing of high point). The acrophase of oxygen consumption occurred on the average about 3 h after the middle of the daily dark span. Maximum insecticide sensitivity, based upon the reciprocal of the LC70, occurred about 2 h earlier. Although the times are fairly close, the difference between the two acrophases was statistically significant.