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Karyotyping is a basic method to investigate chromosomal evolution and genomic rearrangements. Sixteen genera within the basal teleost order Osteoglossiformes are currently described cytogenetically. Our study adds information to this chromosomal dataset by determining the karyotype of Campylomormyrus compressirostris , a genus of African weakly electric fish that has not been previously examined. Our results indicate a diploid chromosome number of 2n = 48 (4sm + 26m + 18a) with a fundamental number of FN = 72. This chromosome number is identical to the number documented for the sister taxon of the genus Campylomormyrus , i.e. , Gnathonemus petersii (2n = 48). These results support the close relationship of Campylomormyrus and Gnathonemus . However, the karyotype formula of C. compressirostris is different from Gnathonemus petersii , thereby confirming the high variability of karyotype formulae within the Mormyridae. We infer that the differences in chromosome number and formula of Campylomormyrus relative to other mormyrids may be caused by Robertsonian fusion and pericentric inversion. In addition to the karyotype description and classification of Campylomormyrus , a ChromEvol analysis was used to determine the ancestral haploid chromosome number of osteoglossiform taxa. Our results indicate a relatively conservative haploid chromosome number of n = 24 for the most recent common ancestor of Osteoglossiformes and for most of the internal nodes of osteoglossiform phylogeny. Hence, we presume that the high chromosome variability evolved recently on multiple independent occasions. Furthermore, we suggest that the most likely ancestral chromosome number of Mormyridae is either n = 24 or n = 25. To the best of our knowledge this is the first attempt to determine and classify the karyotype of the weakly electric fish genus Campylomormyrus and to analyze chromosomal evolution within the Osteoglossiformes based on Maximum Likelihood and Bayesian Inference analyses. [ABSTRACT FROM AUTHOR]

We critically comparedMarcuseniusspecimens from the mouth of the Cunene River on the Namibia/Angola border, a harsh desert environment on the Atlantic Ocean coast virtually devoid of aerial insects with aquatic larvae which are an important food item, withMarcusenius multisquamatusKramer & Wink, 2013 from the escarpment region of that same river, in a relatively rich and productive subtropical savannah environment. River mouth specimens were differentiated in morphology and electric organ discharges, as determined by ANOVA/MANOVA comparisons, principal component and discriminant analyses on morphological and electrophysiological characters, and genetics, including sequences of the mitochondrial cytochromebgene, indicating reproductive isolation. Specimens from the river mouth differed fromM. multisquamatus, their closest relatives, by having a shorter snout, a smaller eye diameter, and smaller nares separation. River mouth specimens were also differentiated from other, increasingly less-close relatives, such asM. altisambesiKramer et al., 2007 from the Okavango River, Botswana, and fromM. krameriMaake et al., 2014 from the Limpopo System, South Africa. We therefore designate the new speciesMarcusenius desertussp. nov. for the Cunene River mouth population. [ABSTRACT FROM PUBLISHER]

Abstract: Active electroreception is an ancestral trait found in many aquatic vertebrates and has evolved independently in two teleost lineages, the Gymnotiformes and the Mormyriformes. Unique to these so-called weakly electric fish is their ability to actively generate electrical currents in the water and sense the electrical properties of the environment. How natural behavior contributes to this sensory system has been of interest to neuroethologists since the pioneering works of Lissmann. Here we report on a mutual modeling and experimental study of the stimuli available during active electrolocation of Gnathonemus petersii (Mormyridae). We show the validity of the model (I) by demonstrating that localized spatial patterns of object induced modulations in the electric field (electric images) are comparable to experimentally mapped 2-dimensional electric images and (II) by replicating earlier key findings showing that a normalized metric of electric image width provides an unambiguous cue for distance estimation. We then show that electric images and the distance metric vary systematically when an object is moved along the trunk. These potential ambiguities with regard to localization lead us to a spatiotemporal analysis of electric images. We introduce a new temporal metric for distance estimation that is based on the normalized spatial properties of electrical images. Finally, based on a survey of exploratory behavior, we show how objects situated at the tail, a region previously neglected, cast global electric images that extend over the whole sensory epithelium of the animals. [Copyright &y& Elsevier]

Marcusenius pongolensis (South Africa) and M. altisambesi (Upper Zambezi/Okavango) differ in the sex difference of their electric organ discharges (EODs). It is permanent and graded in the former and seasonally dimorphic in the latter. Four out of six experimental female M. altisambesi gave significantly stronger responses to the long playback EODs of breeding males rather than short EODs, whereas four of seven experimental males responded in the opposite way (with one exception in association time). When re-tested after a year, the female preference for long EODs had vanished. Both sexes discriminated between playback EODs as either long or short (unlike M. pongolensis), with the cutoff between 1420 and 2470 μs (female EOD average, 350 μs). Exposure to social stimuli from tank neighbours of both sexes did not induce growth of EOD duration in males (unlike M. pongolensis). We suggest that in M. altisambesi the sexually dimorphic male EOD has evolved under female (inter-sexual) selection (in M. pongolensis, both inter- and intra-sexual selection); that there is no evidence for male–male competition (intra-sexual selection, present in M. pongolensis); that ecological differences between a floodplain (M. altisambesi) and a more riverine (M. pongolensis) species may be at the origin of the differentiation. [ABSTRACT FROM AUTHOR]

Abstract: The African weakly electric fish Gnathonemus petersii is well known for its electrosensory capabilities. These animals can detect and distinguish objects through active electrolocation in complete darkness. Because of their nocturnal lifestyle, a low contribution of vision for orientation and object detection has been expected. However, as we show in this review, the retina of G. petersii is highly specialized with hundreds of rods and tens of cones grouped together in bundles in a complex way, ensheathed by a tapetum lucidum. The structure of the bundles goes beyond what would be expected if only photon catch was supposed to be increased. During daytime, the structure of these “macro-receptors” changes dramatically depending on retinomotor movements. During the day, the rods and cones are located in different compartments of the bundle, separated by a narrow canal in the form of a “bottle neck”. Investigations on cell structure and neurochemistry in the retina indicate a general organization that is simpler in terms of bipolar and ganglion cell diversity than in tetrachromatic species such as goldfish, yet similar in terms of neurochemical differentiation of amacrine cells. In both respects, the inner retina of the elephantnose fish bears the greatest similarity to catfish and some deep-sea fish retinae. Neuronal circuits and bundle structure give hints of possible adaptations for contrast and/or movement detection. Behavioral experiments suggest that, in contrast to the vision specialists Lepomis gibbosus, pattern detection of G. petersii is not affected by higher spatial frequencies. A pattern of low spatial frequencies, however, was equally well detected by G. petersii and L. gibbosus. Optomotor response experiments indicate that motion vision is important for Gnathonemus, narrowing down the search for the functional specialization of the Gnathonemus retina and providing a starting point for work on multisensory integration in these fish. [Copyright &y& Elsevier]

Abstract: Electric signals of mormyrid fishes have recently been described from several regions of Africa. Members of the Mormyridae produce weak electric organ discharges (EODs) as part of a specialized electrosensory communication and orientation system. Sympatric species often express distinctive EODs, which may contribute to species recognition during mate choice in some lineages. Striking examples of interspecific EOD variation within assemblages have been reported for two monophyletic radiations: the Paramormyrops of Gabon and the Campylomormyrus of Lower Congo. Here, we describe a speciose assemblage of Petrocephalus in the Lékoli River system of Odzala National Park, Republic of Congo. This widespread genus comprises the subfamily (Petrocephalinae) that is the sister group to all other mormyrids (Mormyrinae). Eleven Petrocephalus species were collected in Odzala, five of which are not described taxonomically. We quantify EOD variation within this assemblage and show that all eleven species produce EOD waveforms of brief duration (species means range from 144 to 663μs) compared to many other mormyrids. We also present reconstructed phylogenetic relationships among species based on cytochrome b sequences. Discovery of the Odzala assemblage greatly increases the number of Petrocephalus species for which EODs and DNA sequence data are available, permitting a first qualitative comparison between mormyrid subfamilies of the divergence patterns that have been described within lineages. We find that the Petrocephalus assemblage in Odzala is not a monophyletic radiation. Genetic divergence among Petrocephalus species often appears higher than among Paramormyrops or Campylomormyrus species. In contrast, results of this study and others suggest that Petrocephalus may generally exhibit less interspecific EOD divergence, as well as smaller sex differences in EOD waveforms, compared to Paramormyrops and Campylomormyrus. We discuss possible causes and consequences of EOD diversification patterns observed within mormyrid subfamilies as a framework for future comparative studies of signal evolution using this emerging model system. [Copyright &y& Elsevier]

The electric organ discharges (EODs) of five mormyrid species ( Marcusenius senegalensis, Brevimyrus niger, Petrocephalus bovei, Pollimyrus isidori, Hippopotamyrus pictus) from different sampling sites from the Upper Volta system in West Africa were investigated. EOD waveforms were recorded at high sampling rates in order to compare signal waveform parameters of the different species from different locations. Except for H. pictus, EODs within a species differed significantly from one another in some parameters and waveform variability at least between some sampling sites. In addition, each species showed a continuous spectrum of waveform variations, all or only parts of which were found at certain localities. Although there was variability and sometimes similarities between species, the EOD waveforms were species specific. Knowing their variation spectrum, they can be used for species determination and are probably used for species recognition by the mormyrids. Similarities or differences in EOD waveform expression within a species were not related to geographical distance. By contrast, we suggest that biotic environmental factors at a given location influence the expression of EOD waveforms. These factors affect absolute measurements such as EOD duration and fast Fourier transformation peak frequency as well as the amount of variation for certain waveform parameters across species in a similar manner for a given site. Although EOD waveform might be important for the establishment of reproductive barriers between species, our results suggest that differences in waveforms may not necessarily reflect different species or speciation processes in progress. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 61–80. [ABSTRACT FROM AUTHOR]

We critically compared local populations of the bulldog fish, Marcusenius macrolepidotus (Peters 1852), from different watersheds, from the furthest south (28° South, South Africa) to the Equator in Kenya. We ascertained allopatric differentiation from topotypical M. macrolepidotus from the Lower Zambezi River (Mozambique) in morphology, electric organ discharges, and molecular genetics for: (1) samples from the Okavango and Upper Zambezi Systems (Botswana and Namibia), (2) samples from South Africa's rivers draining into the Indian Ocean, and (3) samples from the East African Tana River (Kenya). Significant genetic distances in the mitochondrial cytochrome b gene and differing ISSR-PCR profiles corroborate differentiation between the four taxa. We resurrect M. pongolensis (Fowler, 1934) for South Africa (sample 2), and M. angolensis (Boulenger, 1905) for the Quanza River/Angola. We recognize M. altisambesi sp. n. for the Upper Zambezi/Okavango specimens (sample 1), and M. devosi sp. n. for those from Kenya (sample 3). [ABSTRACT FROM AUTHOR]

This is the first description of the ontogenetic development of the electric organ discharge (EOD) in two parapatric mormyrid sibling species, Pollimyrus castelnaui (Boulenger, 1911) and P. marianne Kramer et al. 2003, from the first appearance during the early larval stages at about 0.7 cm total length to the fully developed adult discharge at about 3.0 cm total length. At around day 20 the biphasic larval discharge (which is similar to that of P. adspersus larvae) is followed by the emerging triphasic adult discharge with a delay of about 0.7 ms. Both discharge types coexist for about 3 weeks. As the development advances, the amplitude of the adult discharge increases rapidly while that of the larval discharge diminishes. Whereas the adult EOD waveform of P. marianne remains triphasic later in life, in P. castelnaui an ‘initial flourish’, in the form of additional small phases, is added and develops at an age of about 40 days, when larval and adult EOD are present. Possible evolutionary scenarios are discussed. [ABSTRACT FROM AUTHOR]

Mormyrid fish use active electrolocation to detect and analyze objects. The electrosensory lateral line lobe in the brain receives input from electroreceptors and an efference copy of the command to discharge the electric organ. In curarized fish, we recorded extracellularly from neurons of the electrosensory lateral line lobe while stimulating in the periphery with either a local point stimulus or with a more natural whole-body stimulus. Two classes of neurons were found: (I) three types of E-cells, which were excited by a point stimulus; and (2) two types of I-cells, which were inhibited by point stimulus and responded with excitation to the electric organ corollary discharge. While all neurons responded to a point stimulus, only one out of two types of I-units and two of the three types of E-units changed their firing behavior to a whole-body stimulus or when an object was present. In most units, the responses to whole-body stimuli and to point stimuli differed substantially. Many electrosensory lateral line lobe units showed neural plasticity after prolonged sensory stimulation. However, plastic effects during whole body stimulation were often unlike those occurring during point stimuli, suggesting that under natural conditions electrosensory lateral line lobe network effects play an important role in shaping neural plasticity. [ABSTRACT FROM AUTHOR]

Afferent responses to the fish's own electric organ discharge were explored in the electrosensory lobe of the mormyrid fish Gnathonemus petersii. In order to understand the neural encoding of natural sensory images, responses were examined while objects of different conductivities were placed at different positions along the skin of the fish, i.e. at different points within, and also outside, peripheral receptive fields. The presence of an object in the fish's self-generated electric field produces local modulation of transcutaneous current density. Measurement of the local electric organ discharge shows that object images formed at the electroreceptive sensory surface have an opposing center-surround, 'Mexican hat' profile. This is a pre-receptor phenomenon intrinsic to the physical nature of the sensory stimulus that takes place prior to neural lateral inhibition and is independent of such central inhibition. Stimulus intensity is encoded in the latency and number of action potentials in the response of primary afferent fibers. It is also reflected in changes in the amplitude and area of extracellular field potentials recorded in the deep granular layer of the electrosensory lobe. Since the object image consists of a redistribution of current density over the receptive surface, its presence is coded by change in the activity of receptors over an area much larger than the skin surface facing the object. We conclude that each receptor encodes information coming from the whole scene in a manner that may seem ambiguous when seen from a single point and that, in order to extract specific object features, the brain must process the electric image represented over the whole sensory surface. [ABSTRACT FROM AUTHOR]

Like all mormyrid fish, Brienomyrus brachyistius produces an electric organ discharge (EOD) with a constant waveform and variable sequence of pulse intervals (SPI). Periodic bursts fall into two display categories termed 'scallops' and 'accelerations', with a third category termed 'rasps' that appears to combine the two. The medullary EOD command nucleus (CN) receives excitatory input from the midbrain precommand nucleus (PCN) and the thalamic dorsal posterior nucleus (DP), both of which are regulated by a recurrent inhibitory projection from the ventroposterior nucleus of the torus semicircularis (VP). We tested the following hypotheses: (1) PCN and DP are responsible for generating different burst types (scallops and accelerations, respectively), (2) differences in the strength of recurrent inhibition are related to physiological differences between PCN and DP and (3) recurrent inhibition regulates the resting electromotor rhythm, while disinhibition releases PCN and DP, allowing them to generate bursts. Iontophoresis of the excitatory neurotransmitter L-glutamate (L-Glu) into DP led to acceleration-like output patterns, while in PCN it led to scallop-like output patterns. Iontophoresis of the inhibitory neurotransmitter γ-amino-butyric acid (GABA) into DP and PCN led to an elongation of intervals, as did iontophoresis of L-Glu into VP. Iontophoresis of the GABAA receptor blocker bicuculline methiodide (BMI) into DP and PCN induced repetitive bursting behavior and eliminated differences in the effects of L-Glu iontophoresis in the two nuclei. These results support our three hypotheses, suggesting that production of different communication behaviors may be regulated by spatially distinct groups of neurons, and recurrent inhibition and disinhibition may play an active role in driving and shaping such behaviors. [ABSTRACT FROM AUTHOR]

Over the past 20 years, cladistic analyses have revolutionized our understanding of brain evolution by demonstrating that many structures, some of which had previously been assumed to be homologous, have evolved many times independently. These and other studies demonstrate that evolutionary convergence in brain anatomy and function is widespread. Although there are relatively few neuroethological studies in which brain and behavior have be studied within an evolutionary framework, three relatively well studied cases are reviewed here: electric communication among gymnotiform and mormyriform fishes, prey capture among frogs, and sound localization among owls. These three examples reveal similar patterns of brain evolution. First, it is clear that novel abilities have evolved many times independently in taxa whose common ancestors lack these abilities. Second, it is apparent that small changes in neural pathways can lead to dramatic changes in an organism’s abilities. Brain evolution at this small scale is quite common. The behavioral importance of small scale changes on one hand, and the pervasiveness of convergent evolution on the other, have several implications for understanding brain evolution. First, similar abilities may be conferred by convergent rather than homologous circuits, even among closely related species. Furthermore, closely related species may use the same information in different ways, or they may use different means to obtain the same information. One reason that convergence is so common in the biological world may be that the evolutionary appearance of novel functions is associated with constraints, for example in the algorithms used for a given neural computation. Convergence in functional organization may thus reveal basic design features of neural circuits in species that possess unique evolutionary histories but use similar algorithms to solve basic computational problems.Copyright © 2002 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

East African and south African churchills (Petrocephalus, Mormyridae) were synonymised in 1959 to become members of a single species of subcontinental, southern African distribution, Petrocephalus catostoma (Günther, 1866). By comparison with the type material for P. catostoma from the Ruvuma River and P. stuhlmanni from the Ruvu River, both of East African origin, we confirm the South African form of churchill to represent a new species, P. wesselsi, ranging from the northern Limpopo and Incomati systems south to the Pongola River (Natal) as its southern limit. We also compared churchills from the Sabie River (25° S, South Africa, Incomati system) with churchills from the Upper Zambezi River (17° S, Namibia), using electric organ discharges (EODs) and morphology. The duration of an EOD pulse of the South African form (N = 39; 943.2±S.E. 18.82 µs) is, on average, more than twice that of the Upper Zambezi form (N = 37; 436.6±15.1 µs), and the amplitude of the second head-positive phase (P2 phase relative to P1 = 1) significantly weaker (0.133 ± 0.0005 vs. 0.472 ± 0.002 for Upper Zambezi males, 0.363 ± 0.03 for Upper Zambezi females). In contrast to the Upper Zambezi form, the EOD of the South African form exhibits no difference between the sexes. Fish from the two origins differ significantly in 11 out of 14 anatomical characters studied, confirming molecular genetic differentiation on the species level. [ABSTRACT FROM AUTHOR]

Presents a study on the phylogenetic relationships of both African and South American electric fish orders. Evolutionary biology of the orders Mormyriformes and Gymnotiformes; Methodological rationale; Results and discussion; Conclusions.

The article discusses findings of a study based on a comparison of the retina of the Mormyrids with various other Teleosts. The author of the article informs that for the sake of comparison the retina of a small Cyprinid, Barbus lineomaculatus was studied in detail. This species was chosen because it occurs commonly in the nearby streams so facilitating the collection of fresh material. This fish, in contrast to the Mormyrids which have poor sight, possesses keen powers of vision and the retina is one which has no unusual characters. The retinae of as many Teleosts as possible belonging to the families nearly related to the Mormyrids have been studied.

The authors comment on the recent developments related to research on the behaviour, modulation, evolution and neural mechanisms of behaviour in electric fish. They emphasize the value of weakly electric fish and its neuroethology in the study of neural mechanisms. They describe the electrogenesis of the gymnotiforms and the mormyriforms, the two major groups of weakly electric fishes. They explain how the study of weakly electric fish can aid in the research into the modulation of behaviour.

Examines the Mormyrid fish which uses electric fields to perceive the world around them. Study on how the fish interpret distortions in their self-generatedelectric fields to negotiate theirway around; Measurement of yhe fish's electrical activity while simultaneously recording their neurological responses to a variety of objects.