Evolution of a novel regulatory mechanism of hypoxia inducible factor in hypoxia-tolerant electric fishes.

Hypoxia is a significant source of metabolic stress that activates many cellular pathways involved in cellular differentiation, proliferation, and cell death. Hypoxia is also a major component in many human diseases and a known driver of many cancers. Despite the challenges posed by hypoxia, there are animals that display impressive capacity to withstand lethal levels of hypoxia for prolonged periods of time and thus offer a gateway to a more comprehensive understanding of the hypoxic response in vertebrates. The weakly electric fish genus Brachyhypopomus inhabits some of the most challenging aquatic ecosystems in the world, with some species experiencing seasonal anoxia, thus providing a unique system to study the cellular and molecular mechanisms of hypoxia tolerance. In this study, we use closely related species of Brachyhypopomus that display a range of hypoxia tolerances to probe for the underlying molecular mechanisms via hypoxia inducible factors (HIFs)-transcription factors known to coordinate the cellular response to hypoxia in vertebrates. We find that HIF1⍺ from hypoxia tolerant Brachyhypopomus species displays higher transactivation in response to hypoxia than that of intolerant species, when overexpressed in live cells. Moreover, we identified two SUMO-interacting motifs near the oxygen-dependent degradation and transactivation domains of the HIF1⍺ protein that appear to boost transactivation of HIF1, regardless of the genetic background. Together with computational analyses of selection, this shows that evolution of HIF1⍺ are likely to underlie adaptations to hypoxia tolerance in Brachyhypopomus electric fishes, with changes in two SUMO-interacting motifs facilitating the mechanism of this tolerance.

Ecologically mediated differences in electric organ discharge drive evolution in a sodium channel gene in South American electric fishes.

Active electroreception-the ability to detect objects and communicate with conspecifics via the detection and generation of electric organ discharges (EODs)-has evolved convergently in several fish lineages. South American electric fishes (Gymnotiformes) are a highly species-rich group, possibly in part due to evolution of an electric organ (EO) that can produce diverse EODs. Neofunctionalization of a voltage-gated sodium channel gene accompanied the evolution of electrogenic tissue from muscle and resulted in a novel gene (scn4aa) uniquely expressed in the EO. Here, we investigate the link between variation in scn4aa and differences in EOD waveform. We combine gymnotiform scn4aa sequences encoding the C-terminus of the Nav1.4a protein, with biogeographic data and EOD recordings to test whether physiological transitions among EOD types accompany differential selection pressures on scn4aa. We found positive selection on scn4aa coincided with shifts in EOD types. Species that evolved in the absence of predators, which likely selected for reduced EOD complexity, exhibited increased scn4aa evolutionary rates. We model mutations in the protein that may underlie changes in protein function and discuss our findings in the context of gymnotiform signalling ecology. Together, this work sheds light on the selective forces underpinning major evolutionary transitions in electric signal production.

Biogeochemical water type influences community composition, species richness, and biomass in megadiverse Amazonian fish assemblages.

Amazonian waters are classified into three biogeochemical categories by dissolved nutrient content, sediment type, transparency, and acidity-all important predictors of autochthonous and allochthonous primary production (PP): (1) nutrient-poor, low-sediment, high-transparency, humic-stained, acidic blackwaters; (2) nutrient-poor, low-sediment, high-transparency, neutral clearwaters; (3) nutrient-rich, low-transparency, alluvial sediment-laden, neutral whitewaters. The classification, first proposed by Alfred Russel Wallace in 1853, is well supported but its effects on fish are poorly understood. To investigate how Amazonian fish community composition and species richness are influenced by water type, we conducted quantitative year-round sampling of floodplain lake and river-margin habitats at a locality where all three water types co-occur. We sampled 22,398 fish from 310 species. Community composition was influenced more by water type than habitat. Whitewater communities were distinct from those of blackwaters and clearwaters, with community structure correlated strongly to conductivity and turbidity. Mean per-sampling event species richness and biomass were significantly higher in nutrient-rich whitewater floodplain lakes than in oligotrophic blackwater and clearwater river-floodplain systems and light-limited whitewater rivers. Our study provides novel insights into the influences of biogeochemical water type and ecosystem productivity on Earth's most diverse aquatic vertebrate fauna and highlights the importance of including multiple water types in conservation planning.

Reproductive life-history strategies in a species-rich assemblage of Amazonian electric fishes.

The reproductive biology of only a small fraction of Neotropical freshwater fishes has been described, and detailed comparative studies of reproductive life-history variation in the Neotropical ichthyofauna are lacking. Here we describe interspecific variation in reproductive life history for a multi-species assemblage of the electric knifefish genus Brachyhypopomus (Hypopomidae: Gymnotiformes: Ostariophysi) from Amazonian floodplain and terra firme stream systems. During a year-round quantitative sampling program, we collected and measured key life-history traits from 3,410 individuals. Based on oocyte size distributions, and on circannual variation in gonadosomatic indices, hepatosomatic indices, and capture-per-unit-effort abundance of reproductive adults, we concluded that all species exhibit a single protracted annual breeding season during which females spawn fractionally. We found small clusters of post-larval individuals in one floodplain species and one terra firme stream species, but no signs of parental care. From analyses of body size-frequency distributions and otolith growth increments, we concluded that five species in our study area have approximately one-year (annual) semelparous life history with a single reproductive period followed by death, while two species have a two-year iteroparous life history, with breeding in both year-groups. Despite predictions from life-history theory we found no salient correlations between life history strategy (semelparity or iteroparity) and habitat occupancy (floodplain or terra firme stream). In the iteroparous species B. beebei, we documented evidence for reproductive restraint in the first breeding season relative to the second breeding season and argue that this is consistent with age-regulated terminal investment.

Unexpected species diversity in electric eels with a description of the strongest living bioelectricity generator.

Is there only one electric eel species? For two and a half centuries since its description by Linnaeus, Electrophorus electricus has captivated humankind by its capacity to generate strong electric discharges. Despite the importance of Electrophorus in multiple fields of science, the possibility of additional species-level diversity in the genus, which could also reveal a hidden variety of substances and bioelectrogenic functions, has hitherto not been explored. Here, based on overwhelming patterns of genetic, morphological, and ecological data, we reject the hypothesis of a single species broadly distributed throughout Greater Amazonia. Our analyses readily identify three major lineages that diverged during the Miocene and Pliocene-two of which warrant recognition as new species. For one of the new species, we recorded a discharge of 860 V, well above 650 V previously cited for Electrophorus, making it the strongest living bioelectricity generator.

To see or not to see: molecular evolution of the rhodopsin visual pigment in neotropical electric fishes.

Functional variation in rhodopsin, the dim-light-specialized visual pigment, frequently occurs in species inhabiting light-limited environments. Variation in visual function can arise through two processes: relaxation of selection or adaptive evolution improving photon detection in a given environment. Here, we investigate the molecular evolution of rhodopsin in Gymnotiformes, an order of mostly nocturnal South American fishes that evolved sophisticated electrosensory capabilities. Our initial sequencing revealed a mutation associated with visual disease in humans. As these fishes are thought to have poor vision, this would be consistent with a possible sensory trade-off between the visual system and a novel electrosensory system. To investigate this, we surveyed rhodopsin from 147 gymnotiform species, spanning the order, and analysed patterns of molecular evolution. In contrast with our expectation, we detected strong selective constraint in gymnotiform rhodopsin, with rates of non-synonymous to synonymous substitutions lower in gymnotiforms than in other vertebrate lineages. In addition, we found evidence for positive selection on the branch leading to gymnotiforms and on a branch leading to a clade of deep-channel specialized gymnotiform species. We also found evidence that deleterious effects of a human disease-associated substitution are likely to be masked by epistatic substitutions at nearby sites. Our results suggest that rhodopsin remains an important component of the gymnotiform sensory system alongside electrolocation, and that photosensitivity of rhodopsin is well adapted for vision in dim-light environments.

Electroreception, electrogenesis and electric signal evolution.

Electroreception, the capacity to detect external underwater electric fields with specialised receptors, is a phylogenetically widespread sensory modality in fishes and amphibians. In passive electroreception, a capacity possessed by c. 16% of fish species, an animal uses low-frequency-tuned ampullary electroreceptors to detect microvolt-range bioelectric fields from prey, without the need to generate its own electric field. In active electroreception (electrolocation), which occurs only in the teleost lineages Mormyroidea and Gymnotiformes, an animal senses its surroundings by generating a weak (< 1 V) electric-organ discharge (EOD) and detecting distortions in the EOD-associated field using high-frequency-tuned tuberous electroreceptors. Tuberous electroreceptors also detect the EODs of neighbouring fishes, facilitating electrocommunication. Several other groups of elasmobranchs and teleosts generate weak (< 10 V) or strong (> 50 V) EODs that facilitate communication or predation, but not electrolocation. Approximately 1.5% of fish species possess electric organs. This review has two aims. First, to synthesise our knowledge of the functional biology and phylogenetic distribution of electroreception and electrogenesis in fishes, with a focus on freshwater taxa and with emphasis on the proximate (morphological, physiological and genetic) bases of EOD and electroreceptor diversity. Second, to describe the diversity, biogeography, ecology and electric signal diversity of the mormyroids and gymnotiforms and to explore the ultimate (evolutionary) bases of signal and receptor diversity in their convergent electrogenic-electrosensory systems. Four sets of potential drivers or moderators of signal diversity are discussed. First, selective forces of an abiotic (environmental) nature for optimal electrolocation and communication performance of the EOD. Second, selective forces of a biotic nature targeting the communication function of the EOD, including sexual selection, reproductive interference from syntopic heterospecifics and selection from eavesdropping predators. Third, non-adaptive drift and, finally, phylogenetic inertia, which may arise from stabilising selection for optimal signal-receptor matching.

A new and improved electric fish finder with resources for printed circuit board fabrication

We describe the circuit design, construction, and operation of a field-portable electric fish finder (an AC-coupled wide-band differential bio-amplifier with loudspeaker output). This device permits detection and monitoring of the electric organ discharges generated by neotropical gymnotiform fishes (as well as the mormyroid fishes of tropical Africa). Our design is modified from earlier versions to optimize detection performance and stability over a wider range of ambient water conductivity, including under conditions of extremely low conductivity (< ca. 10 μScm-1). Our new electric fish finder design also incorporates complete waterproofing and longer battery autonomy. We provide Gerber and Eagle files made with the electronic design automation software 'Autodesk Eagle' to allow researchers to order printed circuit boards directly from commercial manufacturers.(AU)

Nós descrevemos o projeto de circuitos eletrônicos e as instrucões para a construção e uso de um detector de peixes elétricos portátil (bio-amplificador diferencial de banda-larga com acoplamento AC). Este aparelho permite a detecção e o monitoramento das descargas de órgãos elétricos gerados por peixes neotropicais da ordem Gymnotiformes (assim como dos peixes mormirídeos da África Tropical). Nosso projeto é modificado a partir de versões anteriores para otimizar o desempenho e a estabilidade sob uma faixa de condutividades ambientais mais ampla, incluindo condições de condutividade extremamente baixa (< ca. 10 μScm-1). Nosso detector de peixes elétricos novo também foi otimizado a fim de proporcionar impermeabilização completa e vida longa para as baterias. Nós fornecemos arquivos 'Gerber' e 'Eagle' preparados com o software de automação de projeto eletrônico 'Autodesk Eagle' para permitir aos pesquisadores a possibilidade de efetuar encomendas de nossa placa de circuito impresso direitamente das empresas de fabricação.(AU)

Revision of Banded Knifefishes of the Gymnotus carapo and G. tigre clades (Gymnotidae Gymnotiformes) from the Southern Neotropics.

Banded Knifefishes (Gymnotus, Gymnotidae) comprise the most species-rich, ecologically tolerant (eurytopic), and geographically widespread genus of Neotropical electric fishes (Gymnotiformes), with 40 valid species occupying most habitats and regions throughout the humid Neotropics. Despite substantial alpha-taxonomic work in recent years, parts of the genus remain characterized by taxonomic confusion. Here we describe and delimit species of the G. carapo and G. tigre clades from the southern Neotropics, using body proportions (caliper-based morphometrics), fin-ray, scale and laterosensory-pore counts (meristics), quantitative shape differences (geometric morphometrics), osteology, color patterns and electric organ discharges. We report these data from 174 Gymnotus specimens collected from 100 localities throughout the southern Neotropics, and delimit species boundaries in a multivariate statistical framework. We find six species of the G. carapo clade (G. carapo australis, G. cuia n. sp., G. chimarrao, G. omarorum, G. pantanal, and G. sylvius), and two species of the G. tigre clade (G. inaequilabiatus and G. paraguensis) in the southern Neotropics. The new species G. cuia is readily distinguished from the morphologically similar and broadly sympatric G. c. australis by a shorter head and deeper head and body, and from the morphologically similar and sympatric G. omarorum by fewer lateral-line ventral rami and fewer pored lateral-line scales anterior to the first ventral ramus. We also review the geographic distributions of all eight species of the G. carapo and G. tigre clades in the southern Neotropics, showing that G. cuia is the most widespread species in the region. These results affirm the importance of understanding the structure of variation within and between species, both geographic and ontogenetic, in delimiting species boundaries.

Melanosternarchus amaru, a new genus and species of electric ghost knifefish (Gymnotiformes: Apteronotidae) from the Amazon Basin.

We describe Melanosternarchus amaru as a new genus and species of Apteronotidae from the deep channels of blackwater and clearwater tributaries of the Amazon River in Brazil and Peru. The new species superficially resembles members of the widespread "Apteronotus" bonapartii species group, from which it can be readily distinguished by expanded bones of the infraorbital laterosensory canal. It can further be distinguished from all other apteronotids by a unique combination of characters: reduced premaxillary dentition, a large gape, and an absence of scales from the entire dorsum. A molecular phylogenetic analysis using three mitochondrial loci and one nuclear locus (~3000 bp) places this genus as sister to Compsaraia, and these two genera together as a clade sister to Pariosternarchus; all nodes with strong statistical support. The clade formed by these three genera includes five species, four of which are restricted to the Amazon basin. The apparent habitat preference of the new species for low-conductivity blackwater and clearwater rivers has not been reported in other apteronotid species.

Revision of Gymnotus (Gymnotiformes: Gymnotidae) from the Upper Madeira Basin of Bolivia and Peru, with descriptions of two new species.

Banded Knifefishes (Gymnotus, Gymnotidae) comprise the most species-rich genus of Neotropical electric fishes, with 41 species currently described from throughout the humid Neotropics, from Mexico to Argentina. Despite substantial alpha-taxonomic work in recent years, the diversity of Gymnotus in some regions remains poorly understood. Here we describe the Gymnotus fauna of the Upper Madeira basin of Bolivia and Peru from examination of more than 240 adult specimens. Species are delimited and described using body proportions (traditional morphometrics), fin-ray, squamation and laterosensory-pore counts (meristics), quantitative shape differences (geometric morphometrics), osteological traits, and color patterns. Comparisons of standardized linear measures as well as multivariate statistical methods validate the presence in the Upper Madeira basin of three previously described species, two with wide-spread geographic distributions throughout Greater Amazonia (G. carapo and G. coropinae), and one (G. chaviro) endemic to southwestern Amazonia. We also diagnose and describe two new species that are endemic to the Upper Madeira basin: G. eyra n. sp., morphologically most similar to G. mamiraua from lowland Amazonia, and G. riberalta n. sp., morphologically most similar to G. pantanal from the Paraguay-Paraná basin. The five Gymnotus species from the Upper Madeira basin are not monophyletic, each species being more closely related to a different species from another region; i.e. the Gymnotus species from the Upper Madeira represents a polyphyletic assemblage. These descriptions to 43 the number of valid Gymnotus species.

Karyotypic Diversity and Evolution in a Sympatric Assemblage of Neotropical Electric Knifefish.

Chromosome changes can perform an important role in speciation by acting as post-zygotic reproductive barriers. The Neotropical electric fish genus Brachyhypopomus (Gymnotiformes, Hypopomidae) has 28 described species, but cytogenetic data are hitherto available only for four of them. To understand karyotype evolution and investigate the possible role of chromosome changes in the diversification of this genus, we describe here the karyotype of eight species of Brachyhypopomus from a sympatric assemblage in the central Amazon basin. We analyzed cytogenetic data in the context of a phylogenetic reconstruction of the genus and known patterns of geographical distribution. We found a strong phylogenetic signal for chromosome number and noted that sympatric species have exclusive karyotypes. Additional insights into the role of chromosome changes in the diversification of Brachyhypopomus are discussed.

Taxonomic revision of the deep channel electric fish genus Sternarchella (Teleostei: Gymnotiformes: Apteronotidae), with descriptions of two new species

This paper provides a taxonomic revision of the Neotropical electric fish genus Sternarchella, with redescriptions of seven valid species and descriptions of two new species. A maximum parsimony analysis of 76 morphological characters from seven ingroup and seven outgroup taxa recovered a non-monophyletic Sternarchella, in which a clade comprising two species with a ventral mouth (S. orinoco + S. sima) is the sister group to a clade comprising seven species that possess a terminal or superior mouth. Nested within this higher-diversity clade is the genus Magosternarchus (recognized herein as a junior synonym of Sternarchella) comprising M. duccis and M. raptor. The Magosternarchus clade forms a polytomy with S. orthos and S. schotti. Sternarchella calhamazon + a new species from the upper Río Madeira (sister species to S. calhamazon), and a new larger-bodied species from the central and upper Río Amazonas also form a clade. Sternarchella orthos is distributed in both the Amazon and Orinoco basins, where it exhibits considerable phenotypic diversity. Sternarchella orthos includes most specimens from the Amazon formerly assigned to the nominal species S. terminalis (recognized herein as a junior synonym of S. schotti).(AU)

Este artigo propõe uma revisão taxonômica do gênero Neotropical de peixe-elétrico Sternarchella, incluindo a redescrição de sete espécies válidas e duas novas espécies. Análise de máxima parcimônia com 76 caracteres morfológicos e amostragem de sete grupos internos e sete grupos externos indica que Sternarchella não constitui grupo monofilético, sendo um clado composto por duas espécies com bocas ventrais (S. orinoco + S. sima) e outro com sete espécies com bocas terminais ou superiores. Dentro deste último clado estão as espécies do gênero Magosternarchus (reconhecido aqui como um sinônimo júnior de Sternarchella): M. duccis e M. raptor. O clado de Magosternarchus forma uma politomia com S. orthos e S. schotti. Sternarchella calhamazon + uma nova espécie do alto rio Madeira (espécie irmã de S. calhamazon) e uma nova espécie de corpo maior do rio Amazonas central e superior também formam um clado. Sternarchella orthos está distribuída nos rios amazônicos e no Orinoco, onde apresenta elevada diversidade fenotípica. Sternarchella orthos inclui a maioria dos espécimes do rio Amazonas anteriormente atribuídos à S. terminalis (considerada neste estudo como sinônimo júnior de S. schotti).(AU)

Electric organ discharges and near-field spatiotemporal patterns of the electromotive force in a sympatric assemblage of Neotropical electric knifefish.

Descriptions of the head-to-tail electric organ discharge (ht-EOD) waveform - typically recorded with electrodes at a distance of approximately 1-2 body lengths from the center of the subject - have traditionally been used to characterize species diversity in gymnotiform electric fish. However, even taxa with relatively simple ht-EODs show spatiotemporally complex fields near the body surface that are determined by site-specific electrogenic properties of the electric organ and electric filtering properties of adjacent tissues and skin. In Brachyhypopomus, a pulse-discharging genus in the family Hypopomidae, the regional characteristics of the electric organ and the role that the complex 'near field' plays in communication and/or electrolocation are not well known. Here we describe, compare, and discuss the functional significance of diversity in the ht-EOD waveforms and near-field spatiotemporal patterns of the electromotive force (emf-EODs) among a species-rich sympatric community of Brachyhypopomus from the upper Amazon.

Phylogenetic Systematics, Biogeography, and Ecology of the Electric Fish Genus Brachyhypopomus (Ostariophysi: Gymnotiformes).

A species-level phylogenetic reconstruction of the Neotropical bluntnose knifefish genus Brachyhypopomus (Gymnotiformes, Hypopomidae) is presented, based on 60 morphological characters, approximately 1100 base pairs of the mitochondrial cytb gene, and approximately 1000 base pairs of the nuclear rag2 gene. The phylogeny includes 28 species of Brachyhypopomus and nine outgroup species from nine other gymnotiform genera, including seven in the superfamily Rhamphichthyoidea (Hypopomidae and Rhamphichthyidae). Parsimony and Bayesian total evidence phylogenetic analyses confirm the monophyly of the genus, and identify nine robust species groups. Homoplastic osteological characters associated with diminutive body size and occurrence in small stream habitats, including loss of squamation and simplifications of the skeleton, appear to mislead a phylogenetic analysis based on morphological characters alone-resulting in the incorrect placing of Microsternarchus + Racenisia in a position deeply nested within Brachyhypopomus. Consideration of geographical distribution in light of the total evidence phylogeny indicates an origin for Brachyhypopomus in Greater Amazonia (the superbasin comprising the Amazon, Orinoco and major Guiana drainages), with subsequent dispersal and vicariance in peripheral basins, including the La Plata, the São Francisco, and trans-Andean basins of northwest South America and Central America. The ancestral habitat of Brachyhypopomus likely resembled the normoxic, low-conductivity terra firme stream system occupied by many extant species, and the genus has subsequently occupied a wide range of terra firme and floodplain habitats including low- and high-conductivity systems, and normoxic and hypoxic systems. Adaptations for impedance matching to high conductivity, and/or for air breathing in hypoxic systems have attended these habitat transitions. Several species of Brachyhypopomus are eurytopic with respect to habitat occupancy and these generally exhibit wider geographical ranges than stenotopic species.

Mitochondrial genomes of the South American electric knifefishes (Order Gymnotiformes).

Three complete mitochondrial genomes of South American electric fishes (Gymnotiformes), derived from high-throughput RNA sequencing (RNA-Seq), are reported herein. We report the complete mitochondrial genome of the bluntnose knifefish Brachyhypopomus n.sp. VERD, determined from newly sequenced data. We also provide the complete mitochondrial genomes for Sternopygus arenatus and the electric eel Electrophorus electricus, assembled from previously published transcriptome data. The mitochondrial genomes of Brachyhypopomus n.sp. VERD, Sternopygus arenatus and Electrophorus electricus have 13 protein-coding genes, 1 D-loop, 2 ribosomal RNAs and 22 transfer RNAs, and are 16,547, 16,667 and 16,906 bp in length, respectively. Phylogenetic analysis of the eight available mitochondrial genomes of gymnotiform fishes shows Apteronotus to be the sister lineage of other gymnotiformes, contradicting the "Sinusoidea" hypothesis that Apteronotidae and Sternopygidae are sister taxa.

A taxonomic revision of the Neotropical electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes: Hypopomidae), with descriptions of 15 new species

The bluntnose knifefish genus BrachyhypopomusMago-Leccia, 1994, is diagnosed from other Rhamphichthyoidea (Rhamphichthyidae + Hypopomidae) by the presence of a disk-like ossification in the anterior portion of the palatoquadrate, and by the following external characters: short snout, 18.7-32.6% of head length (vs. 33.3-68.6% in Hypopomus, Gymnorhamphichthys, Iracema, and Rhamphichthys), absence of a paired accessory electric organ in the mental or humeral region (vs. presence in Hypopygus and Steatogenys), presence of 3-4 pectoral proximal radials (vs. 5 in Akawaio), presence of the antorbital + infraorbital, and the preopercular cephalic lateral line canal bones (vs. absence in Racenisia). Brachyhypopomus cannot be diagnosed unambiguously from Microsternarchus or from Procerusternarchus on the basis of external characters alone. Brachyhypopomus comprises 28 species. Here we describe 15 new species, and provide redescriptions of all 13 previously described species, based on meristic, morphometric, and other morphological characters. We include notes on ecology and natural history for each species, and provide regional dichotomous keys and distribution maps, based on the examination of 12,279 specimens from 2,787 museum lots. A lectotype is designated for Brachyhypopomus pinnicaudatus (Hopkins, Comfort, Bastian & Bass, 1990). Brachyhypopomus species are abundant in shallow lentic and slow-flowing freshwater habitats from southern Costa Rica and northern Venezuela to Uruguay and northern Argentina. Species diversity is highest in Greater Amazonia, where 20 species occur: B. alberti, new species, B. arrayae, new species, and B. cunia, new species, in the upper rio Madeira drainage; B. batesi, new species, in the central Amazon and rio Negro; B. beebei, B. brevirostris, B. regani, new species, B. sullivani, new species, and B. walteri, widespread through the Amazon and Orinoco basins and the Guianas; B. belindae, new species, in the central Amazon basin; B. benjamini, new species, and B. verdii, new species, in the upper Amazon basin; B. bennetti, in the upper, central, and lower Amazon, lower Tocantins, and upper Madeira basins; B. bullocki in the Orinoco, Negro and Essequibo drainages; B. diazi in the Orinoco Llanos; B. flavipomus, new species, and B. hamiltoni, new species, in the central and upper Amazon basin; B. hendersoni, new species, in the central Amazon, lower Negro and Essequibo basins; B. pinnicaudatus in the central and lower Amazon, lower, upper Madeira, lower Tocantins and Mearim basins, and coastal French Guiana; and B. provenzanoi, new species, in the upper Orinoco and upper Negro basins. Five species are known from the Paraná-Paraguay-Uruguay basin and adjacent southern Atlantic drainages: B. bombilla in the lower Paraná, upper, central, and lower Paraguay, Uruguay and Patos-Mirim drainages; B. brevirostris in the upper Paraguay basin; B. draco in the lower Paraná, lower Paraguay, Uruguay, Patos-Mirim, and Tramandaí basins; B. gauderio in the lower Paraná, upper, central, and lower Paraguay, Uruguay, Patos-Mirim and Tramandaí basins; and B. walteri in the lower Paraná and upper Paraguay basins. Two species occur in small Atlantic drainages of southern Brazil: B. janeiroensis in the São João, Paraíba and small intervening drainages; and B. jureiae in the Ribeira de Iguape and Una do Prelado. One species occurs in the middle and upper São Francisco basin: B. menezesi, new species. Three species occur in trans-Andean drainages: B. diazi in Caribbean drainages of northern Venezuela; B. occidentalis in Atlantic and Pacific drainages of southern Costa Rica and Panama to Darién, and the Maracaibo, Magdalena, Sinú and Atrato drainages; and B. palenque, new species, in Pacific drainages of Ecuador.(AU)

Peixes elétricos do gênero Brachyhypopomus Mago-Leccia, 1994, são diagnosticados dos outros Rhamphichthyoidea (Rhamphichthyidae + Hypopomidae) pela presença de uma ossificação discóide na porção anterior do palatoquadrado, e pelos seguintes caracteres externos: focinho curto, 18,7-32,6% do comprimento da cabeça (vs. 33,3-68,6% em Hypopomus, Gymnorhamphichthys, Iracema e Rhamphichthys), ausência de um órgão elétrico acessório pareado na região mental ou humeral (vs. presença em Hypopygus e Steatogenys), presença de 3-4 proximais peitorais radiais (vs. 5 em Akawaio), presença do antiorbital + infraorbital, e dos canais ossificados da linha lateral da região cefálica do pré-opérculo (vs. ausência em Racenisia). Brachyhypopomus não pode ser diagnosticado de maneira não-ambígua de Microsternarchus ou Procerusternarchus, com base em caracteres de morfologia externa. Brachyhypopomus compreende 28 espécies válidas. Aqui nós descrevemos 15 espécies novas, e fornecemos a redescrição de 13 espécies previamente descritas, baseado em caracteres merísticos, morfométricos e outros caracteres morfológicos. Nós incluímos notas sobre à ecologia e história natural para cada uma das espécies, e fornecemos chaves dicotômicas regionais e mapas de distribuição baseado no exame de 12.279 espécimes de 2.787 lotes de museus. Um lectótipo é designado para Brachyhypopomus pinnicaudatus (Hopkins, Comfort, Bastian & Bass, 1990). Espécies de Brachyhypopomus são abundantes em habitats de águas rasas lênticas e com correntes fracas, ocorrendo do sul da Costa Rica e norte da Venezuela ao Uruguai e norte da Argentina. A diversidade de espécies é maior na Grande Amazônia, onde 20 espécies ocorrem: B. alberti, espécie nova, B. arrayae, espécie nova e B. cunia, espécie nova, na drenagem do alto rio Madeira; B. batesi, espécie nova, na Amazônia central e rio Negro; B. beebei, B. brevirostris, B. regani, espécie nova, B. sullivani, espécie nova e B. walteri, amplamente distribuídas nas bacias Amazônicas e do Orinoco, e nas Guianas; B. belindae, espécie nova, bacia Amazônica central; B. benjamini, espécie nova e B. verdii, espécie nova, na bacia do alto Amazonas; B. bennetti, no alto, médio e porções baixas da bacia Amazônica, baixo Tocantins e alto rio Madeira; B. bullocki nas drenagens do Orinoco, Negro e Essequibo; B. diazi nos Llanos do Orinoco; B. flavipomus, espécie nova e B. hamiltoni, espécie nova, no médio e alto Amazonas; B. hendersoni, espécie nova, na Amazônia central, baixo Negro e Essequibo; B. pinnicaudatus no médio e baixo Amazonas, baixo e alto Madeira, baixo Tocantins, bacia do Mearim e rios costeiros da Guiana Francesa; e B. provenzanoi, espécie nova, nas bacias do alto Orinoco e alto Negro. Cinco espécies são conhecidas das bacias Paraná-Paraguai-Uruguai e bacias adjacentes das drenagens do sul do Brasil: B. bombilla no alto, médio e baixo Paraguai, baixo Paraná, Uruguai e drenagens Patos-Mirim; B. brevirostris da bacia do alto Paraguai; B. draco das bacias do baixo Paraguai, baixo Paraná, Uruguai, Patos-Mirim e Tramandaí; B. gauderio das bacias do alto, médio e baixo Paraguai, baixo Paraná, Uruguai, Patos-Mirim e Tramandaí; e B. walteri das bacias do alto Paraguai e baixo Paraná. Duas espécies ocorrem nas drenagens costeiras do sudeste do Brasil: B. janeiroensis no São João, Paraíba e em drenagens menores nas adjacências; e B. jureiae no Ribeira de Iguape e Una do Prelado. Uma espécie ocorre no médio e alto rio São Francisco: B. menezesi, espécie nova. Três espécies ocorrem nas drenagens trans-Andinas: B. diazi nas drenagens do Caribe no norte da Venezuela; B. occidentalis nas drenagens do Atlantico e Pacífico do sul da Costa Rica e Panamá até Darién, e nas drenagens do Maracaibo, Magdalena, Sinú e Atrato; e B. palenque, espécie nova, nas drenagens do Pacífico no Equador.(AU)

Reproductive character displacement and signal ontogeny in a sympatric assemblage of electric fish.

The reproductive signals of two or more taxa may diverge in areas of sympatry, due to selection against costly reproductive interference. This divergence, termed reproductive character displacement (RCD), is expected in species-rich assemblages, where interspecific signal partitioning among closely related species is common. However, RCD is usually documented from simple two-taxon cases, via geographical tests for greater divergence of reproductive traits in sympatry than in allopatry. We propose a novel approach to recognizing and understanding RCD in multi-species communities--one that traces the displacement of signals within multivariate signal space during the ontogeny of individual animals. We argue that a case for RCD can be made if the amount of signal displacement between a pair of species after maturation is negatively correlated to distance in signal space before maturation. Our application of this approach, using a dataset of communication signals from a sympatric Amazonian assemblage of the electric fish genus Gymnotus, provides strong evidence for RCD among multiple species. We argue that RCD arose from the costs of heterospecific mismating, but interacted with sexual selection--favoring the evolution of conspicuous male signals that not only serve for mate-choice, but which simultaneously facilitate species recognition.

On Apteronotus magdalenensis (Miles, 1945) (Gymnotiformes: Apteronotidae): a poorly known species endemic to the río Magdalena basin, Colombia

Based on the examination of the two available paratypes and recently collected material, we present new data and information on the electric knifefish Apteronotus magdalenensis, a species endemic to the río Magdalena-Cauca basin in Colombia. Since Miles' description in 1945, this species was not collected until recent field work at the Torrents of Honda and additional localities. We present data on the external morphology, morphometrics, pigmentation and electric organ discharges (EODs), of A. magdalenensis. We also review its distribution, ecology and conservation status.

Basados en la revisión de los dos paratipos disponibles y material recientemente colectado, presentamos nuevos datos e informaciones del pez cuchillo eléctrico Apteronotus magdalenensis, una especie endémica de la cuenca del río Magdalena-Cauca en Colombia. Desde su descripción en 1945 por Miles, esta especie no fue colectada hasta trabajo de campo llevado a cabo recientemente en los rápidos de Honda y localidades adicionales. Presentamos datos sobre la morfología externa, morformetría, pigmentación y descarga del órgano eléctrico (EOD) de A. magdalenensis. También revisamos su distribución, ecología y estatus de conservación.

Sexual signal evolution outpaces ecological divergence during electric fish species radiation.

Natural selection arising from resource competition and environmental heterogeneity can drive adaptive radiation. Ecological opportunity facilitates this process, resulting in rapid divergence of ecological traits in many celebrated radiations. In other cases, sexual selection is thought to fuel divergence in mating signals ahead of ecological divergence. Comparing divergence rates between naturally and sexually selected traits can offer insights into processes underlying species radiations, but to date such comparisons have been largely qualitative. Here, we quantitatively compare divergence rates for four traits in African mormyrid fishes, which use an electrical communication system with few extrinsic constraints on divergence. We demonstrate rapid signal evolution in the Paramormyrops species flock compared to divergence in morphology, size, and trophic ecology. This disparity in the tempo of trait evolution suggests that sexual selection is an important early driver of species radiation in these mormyrids. We also found slight divergence in ecological traits among closely related species, consistent with a supporting role for natural selection in Paramormyrops diversification. Our results highlight the potential for sexual selection to drive explosive signal divergence when innovations in communication open new opportunities in signal space, suggesting that opportunity can catalyze species radiations through sexual selection, as well as natural selection.