Life history of <Emphasis Type="Italic">Gymnotus refugio</Emphasis> (Gymnotiformes; Gymnotidae): an endangered species of weakly electric fish

The present study describes the life history of Gymnotus refugio, a species classified as Endangered in the last published list of threatened species of the Brazilian fauna. The study was conducted at a conservation unity that protect one of the last remaining semideciduous forests in the region. The reproductive period was estimated as occurring from the end of winter to the last summer months. Gymnotus refugio exibited fractional spawning, the lowest relative fecundity registered among the Gymnotifomes species studied at the present, and male parental care behavior. The analyses showed a seasonal pattern on the species diet, associating different food categories to winter, autumn, and spring. According to food items analysis and estimated intestinal quotient, G. refugio was classified as invertivorous, feeding mainly on autochthonous insects. The results obtained herein suggest that the position of G. refugio as an Endangered species might be influenced by its territoriality, habitat specificity, parental care behavior, and low fecundity, reinforcing the importance of swampy forest environment conservation as the only means of the species maintenance.     

Chromosomal and electric signal diversity in three sympatric electric knifefish species (Gymnotus, Gymnotidae) from the Central Amazon Floodplain

We describe chromosomal and electric signal diversity in three sympatric species of Gymnotus (Gymnotidae) fish from the Central Amazon Floodplain. Gymnotus arapaima presents a karyotype of 2n = 44 (24 m-sm + 20st-a), G. mamiraua 2n = 54 (42 m-sm + 12st-a), and G. jonasi 2n = 52 (12 m-sm + 40st-a). No evidence for a chromosomal sexual system was observed in two species for which both males and females were analyzed (G. mamiraua and G. arapaima). In all three species the constitutive heterochromatin is located primarily in pericentromeric regions, but also at some other sites. G. arapaima and G. mamiraua exhibit simple nucleolar organizing regions (NORs) on short arms of chromosome pairs 19 and 24, respectively. Gymnotus jonasi exhibits a multiple interstitial NOR on the long arm of pairs 9 and 10, and on the short arm of pair 11. G. arapaima and G. mamiraua exhibit several additional similarities in their karyotypic formulas—reflecting the phylogenetic proximity of these species within a G. carapo group clade (based on molecular phylogenetic evidence). The chromosomal differences among these three sympatric species imply complete post-zygotic reproductive isolation. A prominent pattern of partitioning of the peak power frequency of the electric organ discharge of these three species indicates pre-zygotic reproductive isolation of mate attraction signals. We conclude by discussing the evolutionary events that may have promoted signal divergence and reproductive isolation in Gymnotus of the Central Amazon, and the role that chromosomal rearrangements may place in diversification.     

Phylogeny,biogeography, and electric signal evolution of Neotropical knifefishes of the genus Gymnotus (Osteichthyes: Gymnotidae)

The Neotropical knifefish genus Gymnotus is the most broadly distributed and the most diverse (34 + species) gymnotiform genus. Its wide range includes both Central and South American drainages, including the Amazon, Orinoco, and La Plata Basins. Like all gymnotiforms, Gymnotus species produce weak electric fields for both navigation and communication, and these fields exhibit interspecific variation in electric waveform characteristics. Both biogeography and electric signal evolution can profitably be analyzed in a phylogenetic context. Here, we present a total evidence phylogeny for 19 Gymnotus species based on data from the mitochondrial cytochrome b and 16S genes (1558 bp), the nuclear RAG2 gene (1223 bp), and 113 morphological characters. Our phylogenetic hypothesis resolves five distinct Gymnotus lineages. In a previous morphology-based analysis, the Central American Gymnotus cylindricus lineage was hypothesized as the sister group to all other Gymnotus species. In our analysis, the G. cylindricus lineage is nested within South American species, and molecular age estimates support a relatively recent origin for the clade in Central America. Phylogenetic optimization of electric signal waveforms indicate that the ancestral state in Gymnotus is a multiphasic (4 + phases of alternating polarity) condition, and independent phase loss has occurred in multiple lineages. Gymnotus is a model group for understanding Neotropical diversification and the evolution of communication at a continental scale.     

Cytogenetic analysis of three sympatric Gymnotus (Gymnotiformes, Gymnotidae) species verifies invasive species in the Upper Paraná River basin, Brazil

Cytogenetic analyses were performed on three Gymnotus species, Gymnotus paraguensis , Gymnotus sylvius and Gymnotus pantanal , collected in sympatry in the region of Guaíra, Paraná State (Brazil). Gymnotus paraguensis presented 54 chromosomes (52m-sm + 2st) in both sexes, G. sylvius presented 40 chromosomes (36m-sm + 4a) in both sexes and G. pantanal presented 40 chromosomes (14m-sm + 26a) in females and 39 (15m-sm + 24a) in males, with an X₁X₁X₂X₂/X₁X₂Y multiple sex chromosome system. All three species had single nucleolar organizing regions and heterochromatin in the centromeric region of most chromosomes. Gymnotus pantanal , previously collected only in the Lower Paraná and Paraguay River basins, was confirmed for the first time in the Upper Paraná River basin. This species constitutes one of several examples of species that have colonized the region after flooding of the great Sete Quedas waterfalls by the construction of the Itaipu hydroelectric dam. The probable absence or infertility of hybrids is indicated by the high level of chromosome differentiation between these species.     

Molecular characterization and physical mapping of two classes of 5S rDNA in the genomes of Gymnotus sylvius and G. inaequilabiatus (Gymnotiformes, Gymnotidae)

The nucleotide sequences of the 5S rRNA multigene family and their distribution across the karyotypes in 2 species of Gymnotiformes, genus Gymnotus (G. sylvius and G. inaequilabiatus) were investigated by means of fluorescence in situ hybridization (FISH). The results showed the existence of 2 distinct classes of 5S rDNA sequences in both species: class I and class II. A high conservative pattern of the codifying region of the 5S rRNA gene was identified, contrasting with significant alterations detected in the nontranscribed spacer (NTS). The presence of TATA-like sequences along the NTS of both species was an expected occurrence, since such sequences have been associated with the regulation of the gene expression. FISH using 5S rDNA class I and class II probes revealed that both gene classes were collocated in the same chromosome pair in the genome of G. sylvius, while in that of G. inaequilabiatus, class II appeared more disperse than class I.     

Neotropical Monogenoidea. 52. Diechodactylus joaberi n. g., n. sp. from the banded knifefish Gymnotus carapo (Gymnotiformes: Gymnotidae) in southeastern Brazil

Diechodactylus joaberi n. g., n. sp. is described from the body surface of the banded knifefish Gymnotus carapo L. (Gymnotiformes: Gymnotidae) from southeastern Brazil. The new genus is proposed to accommodate species with five pairs of hooks in anterior bilateral clusters on the haptor, three pairs of hooks in a single cluster on the posterior margin of the haptor, sclerites R1 associated with the superficial bar, and confluent intestinal caeca. The presence of five pairs of hooks in two bilateral clusters anterior in the haptor permits the differentiation of species of Diechodactylus from species of all known genera of the Gyrodactylidae. The genus is likely a member of a clade of the Gyrodactylidae comprising genera with a similar hook distribution.     

Comparative anatomy of the cheek muscles of Korean cobitid fishes (Ostariophysi: Cypriniformes), with the comments on their phylogenetic relationships

Cheek muscles of 16 species of all Korean cobitid species belong to six genera were examined and described in detail, with comments on their phylogenetic relationships made on the basis of characteristics of cheek muscles. Korean cobitids were divided into two groups, the Cobitis and Misgurnus groups, by five characters related to three cheek muscles (adductor mandibulae, preorbitalis, and retractor arcus palatine). The former group, comprising Cobitis, Iksookimia, Kichulchoia, Koreocobitis, and Niwaella, is defined by four apomorphies, and the latter, including Misgurnus, by a single apomorphy.     

Directional characteristics of tuberous electroreceptors in the weakly electric fish,Hypopomus (Gymnotiformes)

This paper is an electrophysiological study of the directionality of the tuberous electroreceptors of weakly electric fish. We recorded from two classes of tuberous electroreceptors known for pulse gymnotiforms: Burst Duration Coders (BDCs), and Pulse Markers (PMs). Both code for stimulus amplitude, although the dynamic range for BDCs is greater, and both exhibit strong directional preferences. Polar plots of spike number (for BDCs) or spike threshold (for PMs) versus electric field azimuth, are figure-8 shaped with two asymmetrical, elliptical lobes separated by 180°. The best azimuth of these two types of receptors from a given body region correlate with each other and with measures of best azimuth for transepidermal current flow. The shape and asymmetry of the directionality profiles appear to be caused by filter dynamics of the receptors. Pulse Markers are located on the anterior part of the body surface while Burst Duration Coders are located all over. The best directions of receptors in the anterior third of the body vary systematically with location from 0° to 180°. This region is probably critical for determining the direction of local electric fields. Together these receptors provide the CNS with sufficient information to construct a map of horizontal plane electric field directions.Abbreviations BDC Burst Duration Coder - ELL electrosensory lateral line lobe - EOD electric organ discharge - nALL anterior lateral line nerve - PM Pulse Marker     

Phylogeny of Drosophilinae (Diptera: Drosophilidae), with comments on combined analysis and character support

Drosophilidae (Diptera) is a diverse, cosmopolitan family of flies. Here, we present a combined analysis phylogeny of Drosophilinae, one of the two subfamilies of Drosophilidae, based on data from six different data partitions, including both molecular and morphological characters. Although our data show support for the monophyly of the Hawaiian Drosophilidae, and the subgenus Sophophora, neither the genus Drosophila nor the subgenus Drosophila is monophyletic. Partitioned Bremer support (PBS) indicates that morphological data taken from Grimaldi's monograph (Grimaldi, 1990a), as well as sequences from the mitochondrial (mt) 16S rDNA and the nuclear Adh gene, lend much support to our tree's topology. This is particularly interesting in the case of Grimaldi's data, since his published hypothesis conflicts with ours in significant ways. Our combined analysis cladogram phylogeny reflects the catch-all designation that the name Drosophila has become, in that the cladogram does not support the monophyly of either the genus or subgenus Drosophila.     

Redescription of the teleost Trichomycterus barbouri (Eigenmann, 1911), occurrence in Argentina and comparison with related species (Ostariophysi: Siluriformes: Trichomycteridae)

Trichomycterus barbouri (Eigenmann, 1911) is redescribed based on adult and juvenile specimens, and is distinguished from all congeners by external and osteological characters. The species previously known only from the type locality Beni river in Bolivia, is recorded here the first time for Argentina, from localities in the provinces of Tucumán, Catamarca, Córdoba and Salta. T. barbouri is compared with some Argentinian congeners.     

Ontogeny of the electric organ discharge and the electric organ in the weakly electric pulse fish Brachyhypopomus pinnicaudatus (Hypopomidae, Gymnotiformes)

I recorded the electric organ discharges (EODs) of 331 immature Brachyhypopomus pinnicaudatus 6–88 mm long. Larvae produced head-positive pulses 1.3 ms long at 7 mm (6 days) and added a second, small head-negative phase at 12 mm. Both phases shortened duration and increased amplitude during growth. Relative to the whole EOD, the negative phase increased duration until 22 mm and amplitude until 37 mm. Fish above 37 mm produced a “symmetric” EOD like that of adult females. I stained cleared fish with Sudan black, or fluorescently labeled serial sections with anti-desmin (electric organ) or anti-myosin (muscle). From day 6 onward, a single electric organ was found at the ventral margin of the hypaxial muscle. Electrocytes were initially cylindrical, overlapping, and stalk-less, but later shortened along the rostrocaudal axis, separated into rows, and formed caudal stalks. This differentiation started in the posterior electric organ in 12-mm fish and was complete in the anterior region of fish with “symmetric” EODs. The lack of a distinct “larval” electric organ in this pulse-type species weakens the hypothesis that all gymnotiforms develop both a temporary (larval) and a permanent (adult) electric organ. Accepted: 1 March 1997     

Redescription of the fish parasite Nerocila japonica Schioedte & Meinert, 1881 (Crustacea: Isopoda: Cymothoidae), with comments on previous records of N. acuminata in Japanese waters

Nerocila japonica Schioedte & Meinert, 1881 is redescribed based on the holotype and specimens from various localities in Japanese waters. The following fishes are recorded as new hosts: Tribolodon hakonensis (Cyprinidae), Mugil cephalus, Liza affinis, Chelon haematocheilus (Mugilidae), Lateolabrax japonicus, L. latus (Lateolabracidae), Acanthopagrus latus, A. schlegelii schlegelii (Sparidae), Rhyncopelates oxyrhynchus (Terapontidae), Ditrema viride, D. temminckii temminckii (Embiotocidae), Chaenogobius gulosus, Acanthogobius flavimanus (Gobiidae), Pseudolabrus sp. (Labridae) and Aluterus monoceros (Monacanthidae). Specimens previously recorded as ‘Nerocila acuminata’ from Toyama Bay (the Sea of Japan) were examined, when available, and re-identified as N. japonica. As there has been no reliable record of N. acuminata Schioedte & Meinert, 1881 from off Japan, reports of this species in Japanese waters are considered to represent N. japonica.     

Chromosomal diversity in three species of electric fish (Apteronotidae,Gymnotiformes) from the Amazon Basin

Cytogenetic studies were carried out on samples of Parapteronotus hasemani, Sternarchogiton preto and Sternarchorhamphus muelleri (Apteronotidae, Gymnotiformes) from the Amazon basin. The first two species exhibited both a 2n = 52 karyotype, but differed in their karyotypic formulae, distribution of constitutive heterochromatin, and chromosomal location of the NOR. The third species, Sternarchorhamphus muelleri, was found to have a 2n = 32 karyotype. In all three species the DAPI and chromomycin A3 staining results were consistent with the C-banding results and nucleolar organizer region (NOR) localization. The 18S rDNA probe confirmed that there was only one pair of ribosomal DNA cistron bearers per species. The telomeric probe did not reveal interstitial telomeric sequences (ITS). The karyotypic differences among these species can be used for taxonomic identification. These data will be useful in future studies of these fishes and help understanding the phylogenetic relationships and chromosomal evolution of the Apteronotidae.     

Comparative studies of the aggressive behaviour of two gymnotid electric fish (Gymnotus carapo and Hypopomus artedi).

Electrical and motor behaviour was studied during aggressive interactions in two species of electric fish (Gymnotus carapo and Hypopomus artedi). Paired comparison methods were used to obtain the data, and analysis of the results was undertaken at three different levels: (1) The repertoire of behaviour (motor and electrical); (2) The changes in relative frequency of components with increasing exposure to conspecifics; (3) Sequential analysis of patterns of behaviour occuring both within and between individuals. The results of the three analyses showed: (1) A great similarity in repertoire although a much higher rate of interaction for Gymnotus. The relative importance of the "off" and "burst" signals was reversed for the two species. A prolonged orientation component in Hypopomus was found to be related to the occurrence of discharge synchrony. (2) Habituation of intense components in favour of electrical signalling in both species. (3) Important differences in both the length and structure of sequences.     

Interference with the GABAergic system in the dorsolateral telencephalon and modulation of the electric organ discharge frequency in the weakly electric fish Gymnotus carapo

The functional role of the dorsal portions of dorsolateral telencephalon in modulating the stable electric organ discharge was determined by microinjection of an agonist or antagonist GABAergic drug in the awake weak electric fish, Gymnotus carapo. The dorsolateral telencephalon, which is interconnected with the preglomerular complex and the dorsocentral telencephalic area was microinjected through a guide cannula previously implanted, with different doses of bicuculline, muscimol and saline. Microinjection of bicuculline into the dorsolateral telencephalon induced a complex response consisting of increase, decrease and abrupt interruptions in the frequency of electric organ discharges and an increase in motor activity. Motor activity and modulations in the electric organ discharge are dose dependent. The somatic, but not the electric, effect is abolished under anesthesia by urethane, suggesting that the two responses are parallel but unrelated in terms of occurrence. These data, together with former neuroanatomical findings by this laboratory, suggest two parallel pathways by which the blockage of GABAA receptors in the dorsolateral telencephalon causes modulations in the firing of the medullary pacemaker nucleus. A possible route for the motor effect through reticular projection from the torus semicircularis dorsalis is discussed.     

Interspecific variation in gill size is correlated to ambient dissolved oxygen in the Amazonian electric fish Brachyhypopomus (Gymnotiformes: Hypopomidae)

Gymnotiform electric fish assemblage structure is strongly correlated to dissolved oxygen (DO) availability, which exhibits considerable heterogeneity among Amazonian aquatic systems. DO is known to influence the respiratory morphology of gymnotiform fishes, and yet species-level variation among congeners endemic to alternative DO regimes has not been examined. We describe the DO environment experienced by four congeneric species of gymnotiforms (Brachyhypopomus) and correlate this to quantitative variation in a suite of gill metrics. Whitewater floodplain lakes flanking nutrient-rich whitewater rivers are seasonally hypoxic, exhibiting oxygen concentrations close to 0 mg/l from late April until September. In contrast, DO levels in blackwater floodplain lakes and in terra firme forest stream habitats remain high throughout the year. Two common species of Brachyhypopomus restricted to periodically anoxic whitewater floodplain exhibited a substantially greater gill size than two common species restricted to the perpetually well-oxygenated waters of blackwater floodplain lakes and terra firme stream systems. Discriminant Function Analysis (DFA) based on gill metrics separated the species that live in seasonally anoxic whitewater floodplain species from those that live in perpetually-well oxygenated habitats. Our observations suggest a history of adaptive divergence in the gill morphology of Brachyhypopomus associated with oxygen availability.     

Phylogenetic relationships within the Eurasian cattish family Siluridae (Pisces: Siluriformes), with comments on generic validities and biogeography

A numerical cladistic analysis, based on 23 terminal groups and 63 morphological characters, was done to infer phylogenetic relationships within the Eurasian catfish family Siluridae. Nine hundred and forty-five equally most parsimonious trees (134 steps, consistency index 0.634) were found that differ in their resolutions of four polychotomies. Strict consensus of these trees includes ten internal nodes, does not support monophyly of Silurus, Ompok and Kryptopterus , as usually defined, and offers ambiguous support for monophyly of Wallago. Silurus and Kryptopterus are each composed of two non-sister group clades, and Ompok is composed of at least two such clades. Heuristic searches constrained by monophyly of Silurus, Ompok or Kryptopterus yielded trees five or six steps longer than the shortest trees free of constraints. The strict consensus also infers a basal dichotomy that separates the Siluridae into a temperate Eurasian clade with about 20 nominal species and a subtropical/tropical south and southeast Asian clade with about 75 nominal species. The distributions of these clades overlap in a relatively narrow region of east Asia. A heuristic search for trees 1 step longer than the shortest trees yielded 253890 trees. A strict consensus of these trees also infers a basal dichotomy between the above-mentioned clades. This analysis revealed four additional putative synapomorphies of the Siluridae, pending further resolution of the family's outgroup relationships.     

Phylogenetic relationships within the aplocheiloid fish genus Rivulus (Cyprinodontiformes, Rivulidae): implications for Caribbean and Central American biogeography

We examined the phylogenetic relationships of 16 northern species of the aplocheiloid genus Rivulus inhabiting the Caribbean, Central America, and South America. A total of 714 base pairs per taxon were sequenced from two segments of the mitochondrial genome, 12S rRNA and cytochrome b. Both parsimony and neighbor-joining analyses suggest an ancient vicariant origin of the Greater Antillean taxa, in addition to a quite recent dispersal of species into the Lesser Antilles from the South American mainland. Combined analyses support the monophyly of the northern South American assemblage as the sister group of a Central American/Columbian biota. However, the monophyly of the Central American biota remains uncertain. Divergence estimates for the Central American taxa are calibrated from the Last Cretaceous separation of the proto-Antilles from the Americas. These data suggest that the extant Central American taxa represent the descendants of at least two separate invasions during the Cenozoic, prior to the closing of the Panamanian isthmus. Times are consistent with the extensive evidence for reptilian and mammalian exchange throughout the Cenozoic.