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.     

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.     

Morphology and Interrelationships of Primitive Actinopterygian Fishes

SYNOPSIS. The concept of the Actinopterygii as a natural groupof fishes was not generally accepted until early in this century.Ever since, the characterization of the group has been blurredby the problem of cladistian (polypterid) relationships. Froma review of the structure of polypterids and actinopts, it isconcluded that Cladistia are the sistergroup of Recent actinopterygians(Actinopteri), the two groups together comprising the Actinopterygii.Recent chondrosteans are more closely related to higher actinopts(Neopterygii) than to cladistians. The extinct Palaeonisciformesappear to be a paraphyletic group, comprising stem-group actinopterygians(e.g., Cheirolepts), stem-group actinopterans (e.g., Moythomasia)and relatives of higher actinopterans (e.g., Pteroniscus)     

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.     

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.     

The Evolution of Feeding Motor Patterns in Lizards: Modulatory Complexity and Possible Constraints

Previous research indicated that the evolution of feeding motorpatterns across major taxonomic groups might have occurred withoutlarge modifications of the control of the jaw and hyolingualmuscles. However, the proposal of this evolutionary scheme washampered by the lack of data for some key taxa such as lizards.Recent data on jaw and hyolingual feeding motor patterns ofa number of lizard families suggest extensive variability withinand among species. Although most lizards respond to changesin the structural properties of food items by modulating theactivation of the jaw and hyolingual muscles, some food specialistsmight have lost this ability. Whereas the overall similarityin motor patterns across different lineages of lizards is largefor the hyolingual muscles, jaw muscle activation patterns seemto be more flexible. Nevertheless, all data suggest that boththe jaw and hyolingual system are complexly integrated. Theelimination of feedback pathways from the hyolingual systemthrough nerve transection experiments clearly shows that feedingcycles are largely shaped by feedback interactions. Yet, novelmotor patterns including unilateral control seem to have emergedin the evolution from lizards to snakes.     

The Evolution of Thyroidal Function in Fishes

Although the thyroid gland evolved from the gut, there is noevidence that thyroxine functions as part of the gastro-intestinalendocrine system nor does it have any major function analogousto the control of glucose by the pancreatic islets. The controlof the thyroid evolved from the pituitary control of the gonadsuggesting that an early role of thyroxine was in reproduction.This idea is supported by the presence of cycles of thyroidactivity associated with reproduction in both elasmobranchsand teleosts. In teleosts thyroxine is necessary for gonadalmaturation. The numerous other effects of thyroxine in teleostsmay have evolved from this maturational effect or have beenadded to it during the course of teleost evolution.     

Differences in Feeding Associations of Benthophagous Fishes in two Locations

The feeding associations of two wrasse species (Pseudolabrus; Labridae) with Goniistius zonatus (Cheilodactylidae) in two temperate water locations (Morode and Arakashi) in southern Japan were compared. At both locations, the wrasses accompanied G. zonatus so as to eat benthic invertebrates flushed out by the latter's feeding activities. Although the average feeding frequency of G. zonatus did not differ between the two locations, the host was more frequently and persistently followed at Morode, where foraging hosts often stayed at a calcareous-algal patch for a significant time and repeatedly pecked at the same site (repeated-feeding). At Arakashi, however, characterised by a poor calcareous-algal mat, G. zonatus usually took single sporadic bites at the substrate other than the algal mat while moving about (single-feeding). At both locations, the wrasses accompanied G. zonatus at higher rates when the latter was performing 'repeated-feeding' compared with 'single-feeding', with more frequent pecking by the attendant wrasses in the former association. The differences in feeding association between the two locations apparently resulted from the different patterns of feeding behavior by the host, in turn affected by the feeding substrate composition at each location.     

Evolution of the Vertebrate Cytosolic Malate Dehydrogenase Gene Family: Duplication and Divergence in Actinopterygian Fish

Abstract A general correlation between neural expression and negative charge in isozymes suggests charge represents an adaptation to the neural environment. Interestingly, a notable exception exists in teleost fish. Two cytosolic malate dehydrogenase (MDH) isozymes have different spatial expression patterns in certain fishes: one is expressed in all tissues and the second is expressed primarily in the eye and skeletal muscle. While the neural MDH isozyme is negatively charged, the difference in charge between the two isozymes is not as pronounced as that observed in other gene families (e.g., triosephosphate isomerase and lactate dehydrogenase). Most tetrapods express a single cytosolic MDH isozyme, and it has been demonstrated recently that the pair of isozymes found in teleosts results from a gene duplication sometime after the separation of teleosts and tetrapods, although the exact timing of this duplication has not been inferred. Phylogenetic analyses suggest that the duplication of teleost isozymes occurred during the radiation of actinopterygian fish, consistent with the timing of duplication at other loci. Using inferred amino acid sequences, we examine the pattern of change following the duplication and across the rest of the MDH gene tree. Comparison between the MDH gene family and another gene family that shows a larger charge differential among members (triosephosphate isomerase) indicates that the smaller charge difference between MDH isozymes is best explained by greater constraint on amino acid change directly following the duplication, not greater constraint across the entire gene tree. This difference in constraint might result from the wider pattern of expression of the “neural” MDH isozyme.     

Diversity and Evolution of Body Size in Fishes

The diversity of body sizes observed among species of a clade is a combined result of microevolutionary processes (i.e. natural selection and genetic drift) that cause size changes within phylogenetic lineages, and macroevolutionary processes (i.e. speciation and extinction) that affect net rates of diversification among lineages. Here we assess trends of size diversity and evolution in fishes (non-tetrapod craniates), employing paleontological, macroecological, and phylogenetic information. Fishes are well suited to studies of size diversity and evolution, as they are highly diverse, representing more than 50% of all living vertebrate species, and many fish taxa are well represented in the fossil record from throughout the Phanerozoic. Further, the frequency distributions of sizes among fish lineages resemble those of most other animal taxa, in being right-skewed, even on a log scale. Using an approach that measures rates of size evolution (in darwins) within a formal phylogenetic framework, we interpret the shape of size distributions as a balance between the competing forces of diversification, pushing taxa away from ancestral values, and of conservation, drawing taxa closer to a central tendency. Within this context we show how non-directional mechanisms of evolution (i.e. passive diffusion processes) can produce an hitherto unperceived bias to larger size, when size is measured on the conventional log scale. These results demonstrate how the interpretation of macroecological datasets can be enriched from an historical perspective, and document the ways in which macroevolutionary and microevolutionary processes may be decoupled in the production of size diversity.     

Mammalian Feeding Motor Patterns

Both the anatomy and function of the mammalian masticatory systemhave attracted substantial interest. This review will discussthe general mammalian feeding patterns. An overview will begiven of the evolutionary development and ontogeny of thesepatterns, the influence of occlusal forces, and recent developmentsin computer modeling. In mammals, basic symmetrical food transportcycles have been described for lapping and soft food ingestion.To increase chewing efficiency, a unilateral occlusal motionhas been evolved replacing the slow closing phase in the basiccycle. The relative uniformity of the mammalian jaw-closer motorpatterns during this chewing behavior, as characterized by electromyography(EMG), is striking. Nevertheless, several adaptations, clearlydifferent from the primitive mammalian asymmetric masticatorymotor pattern, can be distinguished. In contrast to the relativeuniformity in motor patterns, the anatomical diversity of jawsystems is impressive and probably reflects the adaptation todiet. Detailed studies on the influence of occlusal force havebeen performed in the last decade. Data suggest that the masticatorycycles are largely shaped by sensory feedback. Also, the sucklingfood intake preceding mastication has been a point of interest.The suckling motor pattern resembles that of mastication, suggestingthat the transition could be gradual during postnatal development.Recently, dynamic computer 3D-modeling has emerged as an analyticaltool. The approach has the potential to help explain how structureand function interact.     

The Physiology and Evolution of Urea Transport in Fishes

This review summarizes what is currently known about urea transporters in fishes in the context of their physiology and evolution within the vertebrates. The existence of urea transporters has been investigated in red blood cells and hepatocytes of fish as well as in renal and branchial cells. Little is known about urea transport in red blood cells and hepatocytes, in fact, urea transporters are not believed to be present in the erythrocytes of elasmobranchs nor in teleost fish. What little physiological evidence there is for urea transport across fish hepatocytes is not supported by molecular evidence and could be explained by other transporters. In contrast, early findings on elasmobranch renal urea transporters were the impetus for research in other organisms. Urea transport in both the elasmobranch kidney and gill functions to retain urea within the animal against a massive concentration gradient with the environment. Information on branchial and renal urea transporters in teleost fish is recent in comparison but in teleosts urea transporters appear to function for excretion and not retention as in elasmobranchs. The presence of urea transporters in fish that produce a copious amount of urea, such as elasmobranchs and ureotelic teleosts, is reasonable. However, the existence of urea transporters in ammoniotelic fish is curious and could likely be due to their ability to manufacture urea early in life as a means to avoid ammonia toxicity. It is believed that the facilitated diffusion urea transporter (UT) gene family has undergone major evolutionary changes, likely in association with the role of urea transport in the evolution of terrestriality in the vertebrates.     

Adaptive Significance of Intra- and Interspecific Differences in the Feeding Repertoires of Cichlid Fishes

Intraspecific modulatory multiplicity in the feeding mechanismof cichlids as elucidated by electromyography has profound implicationson small-scale trophic events the sum of which is the very coreof such large-scale population and evolutionary phenomena asefficiency of trophic exploitation niche width and overlap competitionand adaptation. The greatest paradox emerging from the studyon intra and interspecific differences in feeding repertoiresof cichlid fishes is that the most specialized taxa are notonly remarkable specialists in a narrow sense but also jacks-of-all-trades.If specialists are simultaneously jacks of-all-trades how couldthey have evolved according to the widely accepted hypothesisthat broadening the range of usable resources prevents speciesfrom specializing on individual types? The organism can be considered to be composed of structuralelements and functional components that exert mutual influences.As a result, a network of interacting constraints is set up.The nature of the network determines the direction and rangeof evolutionary changes the possibilities of optimizing adaptationsand built-in variability of the trait. A change in the networkcan put a static trait into a different context to become dynamic.These changes in variability due to changes in the structureof the network cannot be explained in terms of simple adaptationto the external environment. Fitness is considered to dependon the nature of a network of interacting constraints. The possibilitiesof optimization the sensitivity of the phenotypic traits toenvironmental differences and the correlated evolutionary responsesof different traits are all related to this network of interactingconstraints between the elements and components of the organism.Thus the experimental and comparative studies of these networksof interacting constraints should become an increasingly moreimportant focus for morphologists as they attempt to refinetheir understanding of adaptation.     

The Evolution of Male and Female Parental Care in Fishes

In this paper we propose an explanation for (a) the predominanceof male care in fishes, and (b) the phylogenies and transitionsthat occur among care states. We also provide a general evolutionarymodel for studying the conditions under which parental careevolves. Our conclusions are as follows: (i) Parental care hasonly one benefit, the increased survivorship of young. It may,however, have three costs: a "mating cost," an "adult survivorshipcost," and a "future fertility cost." (ii) On average, malesand females will derive the same benefit from care. They probablyalso pay the same adult survivorship cost. However, their matingcost and future fertility costs may differ, (iii) A mating costusually applies only to males. However, this cost may be reducedby male territoriality and, in some situations, be entirelyremoved. Under this condition, natural selection on presentreproductive success is equivalent for males and females, (iv)When fecundity accelerates with body size in females, whilemale mating success follows a linear relationship with bodysize, future fertility costs of parental care are greater forfemales than males. Although further tests are needed, a preliminaryanalysis suggests this often may be the case in fishes. Thus,the predominance of male parental care in fishes is not explainedby males deriving greater benefits from care, but by males payingsmaller future costs. Males thus accrue a greater net fitnessadvantage from parental care (see expressions [6] and [12]).(v) The evolution of biparental care from uniparental male caremay occur because male care selects for larger egg sizes andincreased embryo investment by females. This increases the benefitto the female of parental care, (vi) By contrast, uniparentalfemale care may originate from biparental care when males areselected to desert. This occurs when female care creates a matingcost to males. In some cases male desertion may "lock" femalesinto uniparental care. However, in many other cases femalesmay be selected to desert, giving rise to "no care." (vii) Theorigin of uniparental female care from no care is rare in externallyfertilizing fishes. This is because the benefits of care rarelyoutweigh a female's future fertility costs (expression [9]).For internally fertilizing species, however, the benefit ofcare is high whereas the cost is probably low. Most of thesespecies have evolved embryo retention, (viii) When parentalcare begins with male care and moves to biparental care, ouranalysis suggests that care evolution will include cyclicaldynamics. Parental care in some fishes may thus be seen as transitionaland changing through evolutionary time rather than as an evolutionarilystable state. In theory, "no care" may be a phylogeneticallyadvanced state.     

Distribution Patterns of Indigenous Freshwater Fishes in the Tagus River Basin, Spain

Classification and ordination methods used to examine the internal complexity of the Mediterranean Tagus River catchment based on fish distribution revealed that it is not a homogeneous biogeographical unit. The indigenous fishes analyzed in this study are distributed through the basin forming geographical communities (chorotypes), some of which are associated with environmental factors like river morphology, water quality or geographical location. Nevertheless, 40% of the variation in species occurrence remains unexplained by either environmental or geographical variables, suggesting that historical factors may influence the freshwater fish distribution patterns. Three main biogeographical areas, delimited by significant boundaries, were identified. Two of them are identified as the upper and the middle-lower basins of the Tagus River catchment; the third corresponds to the Alagón River and seems to be linked to historical factors of the catchment.     

几种不同食性鱼类部分血液生化指标的比较研究

采用7020型全自动生化分析仪,测定了黄鳝、鲤鱼、草鱼和鳙鱼血清中总蛋白（TP）、血糖（BG）、甘油三酯（TG）、总胆固醇（TC）、肌酐（creafinine）、尿素（Urea）、尿酸（UA）、磷（P）、钙（Ca）、铁（Fe）和镁（Mg）等11项生化指标,比较研究了这几种不同食性鱼类生化指标的差异.为期二周的饥饿试验,表明黄鳝和鲤鱼等在饥饿状态下生化指标的变化存在较大不同.