Adult neurogenesis in the brain of the Mozambique tilapia, Oreochromis mossambicus

Although the generation of new neurons in the adult nervous system ('adult neurogenesis') has been studied intensively in recent years, little is known about this phenomenon in non-mammalian vertebrates. Here, we examined the generation, migration, and differentiation of new neurons and glial cells in the Mozambique tilapia (Oreochromis mossambicus), a representative of one of the largest vertebrate taxonomic orders, the perciform fish. The vast majority of new cells in the brain are born in specific proliferation zones of the olfactory bulb; the dorsal and ventral telencephalon; the periventricular nucleus of the posterior tuberculum, optic tectum, and nucleus recessi lateralis of the diencephalon; and the valvula cerebelli, corpus cerebelli, and lobus caudalis of the cerebellum. As shown in the olfactory bulb and the lateral part of the valvula cerebelli, some of the young cells migrate from their site of origin to specific target areas. Labeling of mitotic cells with the thymidine analog 5-bromo-2'-deoxyuridine, combined with immunostaining against the neuron-specific marker protein Hu or against the astroglial marker glial fibrillary acidic protein demonstrated differentiation of the adult-born cells into both neurons and glia. Taken together, the present investigation supports the hypothesis that adult neurogenesis is an evolutionarily conserved vertebrate trait.     

Divergence of brain and retinal anatomy and histology in pelagic antarctic notothenioid fishes of the sister taxa Dissostichus and Pleuragramma

The neutrally buoyant Antarctic fishes of the sister taxa Dissostichus (D. eleginoides and D. mawsoni) and Pleuragramma antarcticum diverged early in the notothenioid radiation and filled different niches in the pelagic realm of the developing Southern Ocean. To assess the influence of phylogenetic and ecological factors in shaping neural morphology in these taxa, we studied the anatomy and histology of the brains and retinae, and determined the proportional weights of brain regions. With the brain of the non‐Antarctic sister taxon Eleginops maclovinus as plesiomorphic, statistically significant departures in the brains of the two Antarctic taxa include reduction of the corpus cerebelli and expansion of the mesencephalon and medulla. Compared to Eleginops, both species also have a relatively smaller telencephalon, although this is significant only in Dissostichus. There are a number of apomorphic features in the brain of Pleuragramma including reduced olfactory nerves and bulbs, an extremely small corpus cerebelli and an expanded mesencephalon. Although there is not a significant difference in the relative weights of the medulla in the two taxa, the prominence of the eminentia granularis and bulging cap‐like appearance of the crista cerebellaris are distinctive in Pleuragramma. Brain histology of Dissostichus and Pleuragramma reflects typical perciform patterns and the two species of Dissostichus are histologically identical. Lateral compression in Pleuragramma and notable lobation in Dissostichus also contribute to differences between the taxa. Compression in Pleuragramma is attributable to convergence on an anchovy/herring body shape and to the relatively large brain in this small fish. The less prominent pattern of lobation of the telencephalon, inferior lobes and corpus cerebelli in Pleuragramma probably reflects underlying histology, specifically a reduction in cellularity of the neuropil in the nuclei and lobes. The retinal histology of Dissostichus and Pleuragramma encompasses the extremes seen in Antarctic notothenioids. Dissostichus has a thin scotopic retina with few cones and a high degree of summation. The retina of Pleuragramma is thick and cellular with many small single cones and rods and resembles that of Eleginops. Pedomorphy has not influenced brain morphology in these species but Pleuragramma has superficial neuromasts that are pedomorphic. Although Dissostichus and Pleuragramma are sympatric in the water column, their brains and retinae are highly divergent and reflect the influences of both phylogeny and ecological partitioning of the pelagic realm. Compared to Eleginops, the relatively smaller corpus cerebelli but relatively larger medulla probably indicates, respectively, reduced activity levels of notothenioids in subzero temperatures and expansion of the mechanosensory lateral line system as a supplement to vision under conditions of reduced light. Compared to Dissostichus, Pleuragramma has reduced olfactory bulbs and corpus cerebelli and an expanded mesencephalon. The reduction of the corpus to a small round knob is consistent with physiological parameters and video observations suggesting that, although pelagic, it is relatively inactive. Because mesencephalic weights also include the valvula cerebelli, the relatively large value for Pleuragramma may be attributable to its role in integration and sensorimotor coordination of information from the highly cellular duplex retina and to integration of signals from thewell‐developed octavolateralis system. The brain of Dissostichus displays considerable persistent morphology in its overall resemblance to that of Eleginops, especially the large olfactory bulbs and the relatively large caudally projecting corpus, and Dissostichus exhibits olfactory tracking ability and migratory behavior in common with Eleginops. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

Comparative Study of the Lateral-line System of the Three-spined Stickleback (Gasterosteus aculeatus) and the Nine-spined Stickleback (Pungitius pungitius)

Abstract The morphology of the lateral-line system of the nine-spined stickleback (Pungitius pungitius) and the three-spined stickleback (Gasterosteus aculeatus) has been studied. In the nine-spined stickleback, a preopercular, infraorbital, supraorbital, postotic and peduncular canal can be identified on both sides of the body. Replacement lines are found as a continuation of the preopercular and infraorbital canal. In addition, lines of free neuromasts are found on the mandible and trunk. An accessory line is present above and below the peduncular canal. The presence of both canals and accessory lines on the peduncle suggests that the peduncle in this species has important sensory functions. No canals are found in the three-spined stickleback. Instead, replacement lines corresponding to the canals can be identified on the head. Accordingly, the lateral-line system of the three-spined and the nine-spined stickleback has a different structure. The lateral-line system of both species shows signs of specialization but the three-spined stickleback has a more specialized lateral-line system than the nine-spined stickleback.     

Development of the gigantocerebellum of the weakly electric fish Pollimyrus

The morphogenesis of the "hypertrophied" mormyrid cerebellum was investigated in Pollimyrus (Pisces). Two adults and 36 larvae and young fish raised in captivity were used. Two Gnathonemus petersii adults were taken for comparison. The ontogenetic development of the various cerebellar structures was analysed in inverse chronological order with the aid of serial sagittal and frontal brain sections. Special attention was given to the trilobed corpus cerebelli (C1, C2, C3), the lobi transitorii et caudales, the valvula, the crista cerebelli, the eminentia granularis and the lobus lineae lateralis. 1. The cerebellar structures are of bilateral origin; they develop from the cerebellar and acoustico-lateral "anlage" of the rhombencephalon behind the rhombomesencephalic fissure, either through budding or individualisation and appear between the 4th and 11th day after spawning. The midline fusion of the symmetrical structures is accomplished somewhat later, between the 8th and 23rd days. 2. The cerebellar structures acquire their definitive spatial organisation within 38 days, except for the valvula whose development takes much longer. Recognisable from the 11th day, the valvula upon which ridges are visible from the beginning continues to grow after the 38th day beyond the mesencephalic ventricle, finally overlying the telencephalon frontally and the different rhombencephalic structures caudally. This development, which includes a large antero-lateral folding of the valvula, takes 240 days. 3. Cytological differentiation is just as complex as the general development of the cerebellar structures. Cortical stratification first begins on the 8th to the 11th day in the corpus cerebelli and in the valvula from day 21 to 23 onwards. This differentiation is characterised throughout almost the entire cerebellum by a downward migration of the superficial undifferentiated cells which then constitute the granular layer. In the valvula, the majority of the undifferentiated cells leave the ridges to form a continuous granular layer at the base of the ridges. 4. A differentiation gradient was observed on the antero-posterior axis. 5. In spite of its complexity, the mormyrid cerebellum develops much more rapidly than the cerebellum of the trout.     

Comparative aspects of cerebellar cytoarchitecture in the European eel life cycle

The major anatomical divisions of the cerebellum of the European eel, i.e., corpus cerebelli, lobus vestibulolateralis, and valvula, were studied morphologically and morphometrically. There were differences in cerebellar cytoarchitecture and gross morphology in two stages of the eel life cycle, the trophic stage (yellow eel), and the reproductive stage (silver eel), which are characterized by different degrees of swimming activity. The principal differences between silver and yellow eels in the cytoarchitecture of the corpus cerebelli and the lobus vestibulolateralis were in distribution of Purkinje or Purkinje-like cells in the molecular layer, which is wider in silver eels, in part because of a decreased thickness of the granular cell layer. In the silver eel, the scattering of Purkinje cells was more evident in the lobus vestibulolateralis where the molecular layer is also thicker. The data indicate the transition from the yellow eel to the silver eel is characterized by a migration of granule cells from the ganglionic cell layer to the internal granular layer and by a further development of molecular layer components, e.g., parallel fibers, Purkinje-cell dendrites, etc. In contrast, the thickness of the granular layer and of the Purkinje cell layer, limited to the lower part of the valvula, decreased. There is also a slight increase of cerebellar volume in the silver eel. The volume of the lobus vestibulolateralis was constant. Hypertrophy of the valvula and eminentiae granulares is observed and is due to the migration of cells from the granular layer of the corpus cerebelli whose volume slightly decreases. Perhaps the lobus vestibulolateralis also contributes to the increased volume of eminentiae granulares. Our findings suggest that the cerebellum continues to develop during the passage from the trophic to the reproductive stage of the eel. The appearance of new afferents from the lateral line which becomes more visible in the silver eel probably completes cerebellar ontogeny.     

Anterograde labelling from the optic nerve reveals multiple central targets in the teleost,Lethrinus chrysostomus (Perciformes)

Summary Cobaltous-lysine is transported anterogradely from the optic nerve of the teleost, Lethrinus chrysostomus (Lethrinidae, Perciformes). The marginal optic tract is labelled in longtitudinal bands of light and dark staining fibres which persists caudally within the ventral division but not in the dorsal division. This species possesses multiple central targets in the contralateral preoptic, diencephalic, pretectal, periventricular and tectal regions of the brain. In addition, a greater subdivision of the marginal optic tract is found to project to various nuclei. Ipsilateral projections are found in the suprachiasmatic nucleus and in the region of the horizontal commissure. Projections are also found in the telencephalic region of the nucleus olfactoretinalis and the thalamic region of the nucleus thalamoretinalis. The retinotopicity of some of these nuclei, found in previous studies, is discussed in relation to the possibility of specific sub-populations of retinal ganglion cells having different central targets.Abbreviations used in the Text and Figures A nucleus anteriorthalami - AO accessory optic nucleus - AOT accessory optic tract - AxOT axial optic tract - BO nucleus of the basal optic root - C cerebellum - HCv ventral division of horizontal commissure - I nucleus intermedius thalami - IL inferior lobe - MdOT medial optic tract - MO medulla oblongata - MOTd dorsal division of the marginal optic tract - MOTi intermediate division of the marginal optic tract - MOtv ventral division of the marginal optic tract - O olfactory bulb - OT optic tract - PC nucleus pretectalis centralis - PCo posterior commissure - Pd nucleus pretectalis dorsalis - PG preglomerular complex - PPd nucleus pretectalis periventricularis, pars dorsalis - PPv nucleus pretectalis periventricularis, pars ventralis - PSm nucleus pretectalis superficial pars magnocellularis - PSp nucleus pretectalis superficialis, pars parvocellularis - Sn suprachiasmatic nucleus - TEL telencephalon - TeO optic tectum - TL torus longtitudinalis - TrOlfR tractus olfactoretinalis - VCg granular layer of the valvula cerebelli - VCm molecular layer of the valvula cerebelli - VM nucleus medialis thalami - VL nucleus ventrolateralis thalami - VMdOT ventro-medial optic tract     

Redescription of a rare deep-sea batfish, <Emphasis Type="Italic">Halieutopsis bathyoreos</Emphasis> (Lophiiformes: Ogcocephalidae)

Halieutopsis bathyoreos Bradbury, 1988 (Lophiiformes: Ogcocephalidae), previously described only on the basis of the holotype (62.6mm in standard length) from the central North Pacific, is redescribed on the basis of the holotype and six additional specimens (41.2–68.7mm in standard length) collected from the western South Pacific, off Papua New Guinea, and the western North Pacific, including the Japanese Archipelago. Halieutopsis bathyoreos is distinguished from its congeners by having a shelflike rostrum extending anteriorly well beyond the mouth, a dorsal escal lobe slightly bisected ventrally, an illicial cavity square in outline and completely visible in ventral view, and lacking tubercles on the ventral surface of the disk. The following characters are newly added to the diagnoses of this species: rostrum width 21–29% of head length, tubercles on the dorsal surface of the disk about half the diameter of those on the lateral margin, and 13–15 large lateral-line scales on the tail.     

Neuroecology of cyprinids: comparative,quantitative histology reveals diverse brain patterns

Synopsis Brain patterns are compared by quantitative histology in 28 native and introduced mid-European cyprinid species, considering 17 primary sensory and higher order brain areas. Cluster analysis (CLA) and principal component analysis (PCA) based on relative volumes of these brain areas indicate that cyprinid brains are diversified into four major groups, basic cyprinid, abramine, octavo-lateralis and chemosensory. PCA recognizes the brain of Phoxinus phoxinus as a fifth group. Interspecific differences in brain morphology are mainly caused by variability in relative sizes of the brain stem lobes for external and internal taste (lobus facialis and lobus vagus), as well as of octavo-lateralis and visual areas. Higher order brain areas show little interspecific variation in relative size, and were grouped by PCA according to inter- and intraspecific allometries. Hypotheses on brain functions are based on brain area correlations. We propose that the processing of external taste information in the valvula cerebelli may be particularly important for benthivorous cyprinids, whereas the integration of octavo-lateralis input with visual information via the torus longitudinalis-stratum marginale system may play a key role in the planktivores. Brain patterns suggest two major pathways of cyprinid evolutionary and ecological radiation, one leading from the basic cyprinids towards octavo-lateralis dominated midwater and surface planktivores, the second towards taste-dominated benthivores.     

Systematic implications of brain morphology in potamotrygonidae (Chondrichthyes: Myliobatiformes)

The gross brain morphology, brain proportions, and position of cranial nerves in all four genera (Potamotrygon, Plesiotrygon, Paratrygon, and Heliotrygon) and 11 of the species of the Neotropical stingray family Potamotrygonidae were studied to provide new characters that may have a bearing on internal potamotrygonid systematics. The brain was also studied in four other stingray (Myliobatiformes) genera (Hexatrygon, Taeniura, Dasyatis, and Gymnura) to provide a more inclusive phylogenetic context for the interpretation of features of the brain in potamotrygonids. Our results indicate, based on neuroanatomical characters, that the genera Paratrygon and Heliotrygon are sister groups, as are the genera Potamotrygon and Plesiotrygon, agreeing with previous morphological and molecular phylogenetic studies. Both groups of genera share distinct conditions of the olfactory tracts, telencephalon and its central nuclei, hypophysis and infundibulum, morphology and orientation of the metencephalic corpus cerebelli, orientation of the glossopharyngeal nerve, and overall encephalic proportions. The corpus cerebelli of Paratrygon and Heliotrygon is interpreted as being more similar to the general batoid condition and, given their phylogenetic position highly nested within stingrays, is considered secondarily derived, not plesiomorphically retained. Our observations of the corpus cerebelli of stingrays, including Hexatrygon, corroborate that the general stingray pattern previously advanced by Northcutt is derived among batoids. The morphology of the brain is shown to be a useful source of phylogenetically informative characters at lower hierarchical levels, such as between genera and species, and thus, has significant potential in phylogenetic studies of elasmobranchs. J. Morphol. 277:252–263, 2016. © 2015 Wiley Periodicals, Inc.     

The Saurida undosquamis group (Aulopiformes: Synodontidae), with description of a new species from southern Japan

Four lizardfishes of Saurida (family Synodontidae), S. undosquamis, S. umeyoshii sp. nov., S. macrolepis, and S. longimanus, are described. All are recognized here as the Saurida undosquamis group, characterized by having dark dots on the upper margin of the caudal fin, pectoral fin exceeding origin to pelvic fin, anterior rays of dorsal fin neither elongate nor filamentous, predorsal length greater than distance between dorsal-fin and adipose-fin origins, 46–55 pored lateral-line scales, and vomer with 0–8 teeth. Saurida undosquamis, from northern West India and West Pacific, excluding East Asia, differs from others in having lateral-line scales ridged on the caudal peduncle, conspicuously concave posterior margin of the pectoral fin, 51–55 pored lateral-line scales, and 50–53 vertebrae. Saurida umeyoshii sp. nov., from southern Japan and the East China Sea, is defined by three rows of indistinct dark blotches on, above, and below the lateral line, distribution of scale pockets with melanophores on their posterior part extending over the entire abdominal region from the lateral line in specimens over ca. 130 mm SL, lateral-line scales not ridged on caudal peduncle, 49–52 pored lateral-line scales, and 48–50 vertebrae. Saurida macrolepis, from the Indo-West Pacific, is characterized by 46–49 pored lateral-line scales and 45–48 vertebrae. Saurida longimanus, from northern West India, northwest Australia, and southern Indonesia, differs from the others in having a long pectoral fin extending past the origin of the dorsal fin. Some geographic variations are found in S. macrolepis. Saurida grandisquamis is confirmed as a junior synonym of S. undosquamis, based on examination of the type specimens. A key to species in the S. undosquamis group is included.     

Immunocytochemical distribution of FMRFamide-like substance in the brain of the cloudy dogfish,Scyliorhinus torazame

Summary The distribution of the molluscan cardioexcitatory tetrapeptide FMRFamide (Phe-Met-Arg-Phe-NH₂) in the brain of the cloudy dogfish, Scyliorhinus torazame, was examined by immunocytochemistry. FMRFamide-like immunoreactivity was demonstrated to occur extensively in various regions of the dogfish brain, except for the corpus cerebelli. Immunoreactive neuronal perikarya were located in the ganglion of the nervus terminalis, the preoptic area, and the hypothalamic periventricular gray matter consisting of the nucleus medius hypothalamicus, the nucleus lateralis tuberis, and the nucleus lobi lateralis. some of the immunoreactive cells in the hypothalamus were identified as cerebrospinal fluid-contacting neurons. The bulk of the immunostained fibers in the nervus terminalis penetrated into the midventral portion of the telencephalon and ran dorsocaudally toward the basal telencephalon and hypothalamus, showing radial projections or ramifications. The labeled fibers were abundant in the midbasal part of the telencephalon and in the hypothalamus, where some fibers were found in loose networks around the cell bodies of the nucleus septi and hypothalamic periventricular nuclei. The fibers demonstrated in the hypothalamus terminated around the vascular wall of the primary capillary plexus of the median eminence or penetrated deeply into the pars intermedia of the hypophysis. These results suggest that, in the dogfish, an FMRFamide-like substance participates in the regulation of adenohypophysial function. This molecule may have a role as a neurotransmitter and/or neuromodulator in the central nervous system.     

A neuroanatomical study on the organization of the central antennal pathways in insects

Summary Receptor cell axons from the antennal flagellum terminate in the glomeruli of the ipsilateral deutocerebrum in Periplaneta americana and Locusta migratoria. Processes from several groups of deutocerebral neurons also enter the glomeruli and terminate in characteristic branching patterns. There, they contact the antennal axons. Connections are both convergent and divergent. Not only do single central neurons collect the inputs from many receptor cells, but receptor axons were often observed to branch and terminate at more than one deutocerebral neuron. The axons from a portion of the neurons go to form the deutocerebral bundle of the tractus olfactorioglobularis. These axons of the bundle terminate in the ipsilateral calyx of the corpus pedunculatum and in the lateral lobus protocerebri. The processes of the majority of the deutocerebral neurons stay within the deutocerebrum itself and may serve as local interneurons. Part of some antennal fibers terminate in the lobus dorsalis. The lobus glomeratus receives inputs from the maxillary palps and also from processes of deutocerebral neurons.Electron microscopy of synaptic connections and anatomical experiments reveal a complicated pattern of connections between receptor axons and higher order neurons as well as between higher order neurons themselves within the glomeruli.The ratio of the number of antennal fibers to that of relay fibers could easily lead to the interpretation, that the deutocerebrum merely serves as a device for reducing the number of transmission channels. However, coupled with physiological data, anatomical details such as conand divergence of input and interconnections between input channels suggest rather a filtering system and a highly complicated integrative network.     

Freeze-fracture study of the lateral-line canal organ of the Japanese sea eel,Lincozymba nystromi

Summary Specializations of apical surfaces of hair cells, supporting cells and marginal cells in the lateral-line canal organ of Japanese sea eel, Lincozymba nystromi, were examined with a freeze-fracture technique. Apical surfaces of hair cells have a lower density of intramembrane particles (IMP) than those of the surrounding supporting cells. Density of IMP on the streocilia is almost the same as that on the apical surface of hair cells. Junctions between hair and supporting cells were tighter than those between two supporting cells; those between supporting and marginal cells were tighter than those between hair and supporting cells, and those between two marginal cells were the tightest in the lateral-line canal organ.     

Genetics of osteal plate polymorphism and microevolution of threespine stickleback (Gasterosteus aculeatus L.)

Summary The results of genetical studies of osteal plate polymorphism of threespine stickleback Gasterosteus aculeatus reported to date (Munzing 1959; Hagen and Gilbertson 1973; Avise 1976) are discussed and proposed inheritance models are considered. Results of crosses between the morphs of G. aculeatus from the White Sea are presented. An attempt has been made by the author to devise a unifying model for the inheritance of plate morphs within the whole range of G. aculeatus. The role of polymorphism in the microevolutionary processes taking place within this complex species is discussed.     

Sex-related variability of rostrum morphometry of Aristeus antennatus (Decapoda: Aristeidae) from the Ionian Sea (Eastern Mediterranean, Greece)

Sex-related rostral variability was studied in the aristeid shrimp Aristeus antennatusfrom the Eastern Ionian Sea (Mediterranean). Shrimps were collected on a monthly basis from December 1996 to November 1997 using a commercial bottom trawl in a depth range of 446–728 m. Female relative growth of rostrum proved to be negative allometric both seasonally and in the pooled annual data set. Males on the other hand, showed no or negative correlation of rostrum length with size. Mature males with short rostra dominated in the male population all year around. The appearance of males with long and intermediate rostra during winter, which disappear thereafter in favour of those with short rostra, indicates that rostrum shortening takes place during the end of winter. The increase of mated females during spring supports the hypothesis already addressed by other authors on the function of the male short rostrum in this species mating behaviour. Nevertheless, the paucity, in comparison to other Mediterranean populations, of males with long or intermediate rostra could indicate that for the bulk of the male population, the process of rostrum shortening in the Eastern Ionian Sea occurs outside the geographical locality or depth range sampled.     

Body Size and the Maintenance of Reproductive Isolation in Stickleback,Genus Gasterosteus

The blackspotted stickleback Gasterosteus wheatlandi and the widely studied threespine stickleback G. aculeatus are sympatric throughout the former’s range and share many aspects of life history and reproductive behaviour. These two species differ significantly in size, with G. wheatlandi of both sexes measured at approximately 60% of the standard length of their G. aculeatus counterparts. This study concentrated on G. wheatlandi courtship behaviour and investigated its role in the maintenance of reproductive isolation with G. aculeatus. Specifically, the roles that (1) female body size plays in influencing male courtship preferences and (2) male body size and behaviour play in female courtship preferences were investigated through dummy and live conspecific and heterospecific stimulus presentations. Male G. wheatlandi courtship preferences are consistent with previously described patterns for G. aculeatus. Males of both species preferentially approach and court the larger of two simultaneously presented live or dummy females. Thus, the smaller G. wheatlandi males are indiscriminate with respect to assortative mate choice; not only preferring to approach and court more fecund conspecific females but, more significantly, G. aculeatus‐sized females. In contrast, females of both species demonstrate strong assortative courtship preferences. When presented with pairs of flask‐enclosed males, females of both species preferentially orient and court the conspecific male over the heterospecific. Similarly, when presented with a conspecific male and a heterospecific male presented singly, females prefer to enter the nest of the conspecific. Systematic analysis of the interactions between these pairs of fish (one male, one female) demonstrates that the breakdown of courtship in heterospecific courtship occurs late in the courtship sequence when the widely differing forms of male leading behaviour results in drastically differing female responses. I suggest that, as previously described in G. aculeatus, the supernormality effect plays a significant role in mediating adaptive mate choice behaviour in G. wheatlandi. However, the added element of a larger sympatric species introduces a possible cost in time and energy devoted to courting heterospecific, and sympatric, females that the larger G. aculeatus do not likely incur. There is substantial evidence from many sympatric G. aculeatus species pairs that there is assortative mate choice based on size and/or courtship behaviour. Courtship trials suggest a more pervasive role for females in assortative mate choice. Whether it is male body size per se, or in combination with behaviour, morphology or other cues, is unresolved in the present study.     

Synapse-like contacts between axons of the pineal tract and the subcommissural organ in Rana perezi (Anra) and their absence in Carassius auratus (Teleostei): ultrastructural tracer studies

The present study was designed to investigate the controversial subject of the existence of a neural input from the pineal organ via the pineal tract to the subcommissural organ (SCO) in teleosts and anurans. Horseradish peroxidase was injected into the pineal organ and pineal tract of Carassius auratus and Rana perezi. Within the pinealofugal fibers the tracer was visualized at the light-and electron-microscopic levels either by immunocytochemistry using an anti-peroxidase serum, or by revealing the enzymatic activity of peroxidase. In both species, labeled myelinated and unmyelinated fibers of the pineal tract were readily traced by means of electron microscopy. In R. perezi, numerous terminals contacting the SCO cells in a synapse-like (synaptoid, hemisynaptic) manner bore the label, whereas a different population of endings was devoid of the tracer, indicating that in this species the SCO receives a dual neural input, one of pineal origin, the other of unknown source and nature. In the SCO of C. auratus, neither labeled nor unlabeled synapse-like contacts were found. Thus, in this latter species, a direct neural input to the SCO is missing. It is concluded that the secretory activity of the SCO can be controlled by different mechanisms in different species, and that more than one neural input mechanism may operate in the same species.     

Estimating position and velocity of a submerged moving object by the clawed frog Xenopus and by fish—A cybernetic approach

The lateral-line system is a unique facility of aquatic animals to locate predator, prey, or conspecifics. We present a detailed model of how the clawed frog Xenopus, or fish, can localize submerged moving objects in three dimensions by using their lateral-line system. In so doing we develop two models of a slightly different nature. First, we exploit the characteristic properties of the velocity field, such as zeros and maxima or minima, that a moving object generates at the lateral-line organs and that are directly accessible neuronally, in the context of a simplified geometry. In addition, we show that the associated neuronal model is robust with respect to noise. Though we focus on the superficial neuromasts of Xenopus the same arguments apply mutatis mutandis to the canal lateral-line system of fish. Second, we present a full-blown three-dimensional reconstruction of the source on the basis of a maximum likelihood argument.     

Behaviorally measured tactile sensitivity in the common bottlenose dolphin,Tursiops truncatus

Little research has been conducted on the somatosensory system of toothed whales and it remains uncertain how tactile sensitivity varies about their bodies. In this study, tactile sensitivity to high-frequency (250-Hz) displacement of the skin was quantified in three trained adult common bottlenose dolphins (Tursiops truncatus) using a vibratory device (tactor). The magnitude of skin displacement was controlled by varying the voltage to the tactor held against the skin surface with a constant force. Tactile thresholds were determined using an adaptive method of limits in which dolphins reported perception of the tactile stimulus by producing a whistle. Displacement thresholds ranged from 2.4 to 40 μm, with the greatest sensitivity found along the rostrum, melon, and blowhole. Sensitivity decreased caudally along the body, with the dorsal fin and tip of the fluke being the least sensitive locations tested. The results support hypotheses that the follicles on the dolphin rostrum are particularly important for perception. The reduction in tactile sensitivity at the appendages is consistent with their primary role in stabilization and locomotion compared to exploration or environmental sensing.     

Daphnia (Ctenodaphnia) Mediterranea: A new species of hyperhaline waters,long confused with D. (C.) Dolichocephala Sars, 1895.

A very particular form of Daphnia (Ctenodaphnia), adapted to life in epicontinental hyperhaline waters of Mediterranean arid regions had long been confused with Daphnia (Ctenodaphnia) dolichocephala Sars, 1895. In this paper the morphological and ecological differences between the two taxa are pointed out and comparison is made with another closely related Rumanian form (Daphnia cf. mediterranea) and with the related Spanish species (D. atkinsoni and D. chevreuxi). The Daphnia of saline environments is described here as Daphnia (Ctenodaphnia) mediterranea. The most important differential characters of this new species are: 1) the short and widely rounded rostrum; 2) dorsal ridge of the female extends to the anteriormost part of the head; 3) elliptical ephippium with a ride anterior margin; convex shape and separate from the dorsal ridge; 4) males possessing a very long antennule base that reaches the distal limit of the head.