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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.

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The catfish family Heptapteridae is ubiquitous across a range of freshwater habitats from southern Mexico to northern Argentina and contains 23 genera and 228 valid species. After a century of mostly morphology-based systematic analyses of these fishes, we provide the first molecular phylogenetic hypothesis spanning most valid Heptapteridae genera (16 of 23). We examined eight of 14 valid genera in the Nemuroglanis-subclade (Heptapterini), all valid genera in the Brachyglanis-subclade (Brachyglaniini) and most valid Brachyglaniini species (11 of 15). Maximum likelihood and Bayesian analyses of a 4156-base alignment of five gene regions (three mitochondrial: COI, Cyt b, and ND2; two nuclear: RAG2, Glyt) yielded thoroughly resolved and statistically robust phylogenies that were largely congruent with each other and with previous morphology-based hypotheses. We propose a revised phylogenetic classification consisting of two subfamilies (Rhamdiinae, Heptapterinae) each with two tribes. Dense taxonomic sampling of Brachyglaniini, including type species of Brachyglanis, Gladioglanis, Leptorhamdia, and Myoglanis, revealed widespread paraphyly. Newly recovered clades within Brachyglaniini are closely associated with either the upper Orinoco or the Essequibo suggesting repeated dispersals and/or range expansions/contractions across the western Guiana Shield highlands and from there to the upper Amazon and Brazilian Shield. These biogeographical processes appear to have been an important driver of allopatric diversification in the clade.

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Rhodopsin, the light-sensitive visual pigment expressed in rod photoreceptors, is specialized for vision in dim-light environments. Aquatic environments are particularly challenging for vision due to the spectrally dependent attenuation of light, which can differ greatly in marine and freshwater systems. Among fish lineages that have successfully colonized freshwater habitats from ancestrally marine environments, croakers are known as highly visual benthic predators. In this study, we isolate rhodopsins from a diversity of freshwater and marine croakers and find that strong positive selection in rhodopsin is associated with a marine to freshwater transition in South American croakers. In order to determine if this is accompanied by significant shifts in visual abilities, we resurrected ancestral rhodopsin sequences and tested the experimental properties of ancestral pigments bracketing this transition using in vitro spectroscopic assays. We found the ancestral freshwater croaker rhodopsin is redshifted relative to its marine ancestor, with mutations that recapitulate ancestral amino acid changes along this transitional branch resulting in faster kinetics that are likely to be associated with more rapid dark adaptation. This could be advantageous in freshwater due to the redshifted spectrum and relatively narrow interface and frequent transitions between bright and dim-light environments. This study is the first to experimentally demonstrate that positively selected substitutions in ancestral visual pigments alter protein function to freshwater visual environments following a transition from an ancestrally marine state and provides insight into the molecular mechanisms underlying some of the physiological changes associated with this major habitat transition.

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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.

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A fundamental challenge for both sustainable fisheries and biodiversity protection in the Neotropics is the accurate determination of species identity. The biodiversity of the coastal sharks of Guyana is poorly understood, but these species are subject to both artisanal fishing as well as harvesting by industrialized offshore fleets. To determine what species of sharks are frequently caught and consumed along the coastline of Guyana, we used DNA barcoding to identify market specimens. We sequenced the mitochondrial co1 gene for 132 samples collected from six markets, and compared our sequences to those available in the Barcode of Life Database (BOLD) and GenBank. Nearly 30% of the total sample diversity was represented by two species of Hammerhead Sharks (Sphyrna mokarran and S. lewini), both listed as Endangered by the International Union for Conservation of Nature (IUCN). Other significant portions of the samples included Sharpnose Sharks (23% - Rhizoprionodon spp.), considered Vulnerable in Brazilian waters due to unregulated gillnet fisheries, and the Smalltail Shark (17% - Carcharhinus porosus). We found that barcoding provides efficient and accurate identification of market specimens in Guyana, making this study the first in over thirty years to address Guyana's coastal shark biodiversity.(AU)

Um desafio fundamental para a pesca sustentável e a proteção da biodiversidade nos neotrópicos é a identificação precisa das espécies. A biodiversidade dos tubarões costeiros da Guiana é pouco compreendida, porém essas espécies estão sujeitas tanto à pesca artesanal quanto à pesca industrializada não costeira. Para determinar quais espécies de tubarões são frequentemente capturadas e consumidas ao longo do litoral da Guiana, utilizamos DNA barcoding para identificar espécimes comumente encontrados e adquiridos em mercados. Nós sequenciamos o gene mitocondrial coI para 132 espécimes adquiridos de seis mercados e comparamos estas sequências com as disponíveis no Barcode of Life Database (BOLD) e GenBank. Quase 30% da diversidade total amostrada foi constituída por duas espécies de tubarões martelo (Sphyrna mokarran e S. lewini), ambas listadas como espécies ameaçadas pela UICN. Outras porções significativas da amostragem incluem Cações-Frango (23% - Rhizoprionodon spp.), considerados vulneráveis em águas brasileiras, devido a pesca de arrasto não regulamentada, e o Cação-azeiteiro (17% - Carcharhinus porosus). Descobrimos que o barcoding é uma forma identificação eficiente e precisa para espécimes de mercado na Guiana, tornando este estudo o pioneiro na documentação da biodiversidade dos tubarões costeiros da Guiana.(AU)

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A fundamental challenge for both sustainable fisheries and biodiversity protection in the Neotropics is the accurate determination of species identity. The biodiversity of the coastal sharks of Guyana is poorly understood, but these species are subject to both artisanal fishing as well as harvesting by industrialized offshore fleets. To determine what species of sharks are frequently caught and consumed along the coastline of Guyana, we used DNA barcoding to identify market specimens. We sequenced the mitochondrial co1 gene for 132 samples collected from six markets, and compared our sequences to those available in the Barcode of Life Database (BOLD) and GenBank. Nearly 30% of the total sample diversity was represented by two species of Hammerhead Sharks (Sphyrna mokarran and S. lewini), both listed as Endangered by the International Union for Conservation of Nature (IUCN). Other significant portions of the samples included Sharpnose Sharks (23% - Rhizoprionodon spp.), considered Vulnerable in Brazilian waters due to unregulated gillnet fisheries, and the Smalltail Shark (17% - Carcharhinus porosus). We found that barcoding provides efficient and accurate identification of market specimens in Guyana, making this study the first in over thirty years to address Guyana's coastal shark biodiversity.(AU)

Um desafio fundamental para a pesca sustentável e a proteção da biodiversidade nos neotrópicos é a identificação precisa das espécies. A biodiversidade dos tubarões costeiros da Guiana é pouco compreendida, porém essas espécies estão sujeitas tanto à pesca artesanal quanto à pesca industrializada não costeira. Para determinar quais espécies de tubarões são frequentemente capturadas e consumidas ao longo do litoral da Guiana, utilizamos DNA barcoding para identificar espécimes comumente encontrados e adquiridos em mercados. Nós sequenciamos o gene mitocondrial coI para 132 espécimes adquiridos de seis mercados e comparamos estas sequências com as disponíveis no Barcode of Life Database (BOLD) e GenBank. Quase 30% da diversidade total amostrada foi constituída por duas espécies de tubarões martelo (Sphyrna mokarran e S. lewini), ambas listadas como espécies ameaçadas pela UICN. Outras porções significativas da amostragem incluem Cações-Frango (23% - Rhizoprionodon spp.), considerados vulneráveis em águas brasileiras, devido a pesca de arrasto não regulamentada, e o Cação-azeiteiro (17% - Carcharhinus porosus). Descobrimos que o barcoding é uma forma identificação eficiente e precisa para espécimes de mercado na Guiana, tornando este estudo o pioneiro na documentação da biodiversidade dos tubarões costeiros da Guiana.(AU)

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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.

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The electric communication signals of weakly electric ghost knifefishes (Gymnotiformes: Apteronotidae) provide a valuable model system for understanding the evolution and physiology of behavior. Apteronotids produce continuous wave-type electric organ discharges (EODs) that are used for electrolocation and communication. The frequency and waveform of EODs, as well as the structure of transient EOD modulations (chirps), vary substantially across species. Understanding how these signals have evolved, however, has been hampered by the lack of a well-supported phylogeny for this family. We constructed a molecular phylogeny for the Apteronotidae by using sequence data from three genes (cytochrome c oxidase subunit 1, recombination activating gene 2, and cytochrome oxidase B) in 32 species representing 13 apteronotid genera. This phylogeny and an extensive database of apteronotid signals allowed us to examine signal evolution by using ancestral state reconstruction (ASR) and phylogenetic generalized least squares (PGLS) models. Our molecular phylogeny largely agrees with another recent sequence-based phylogeny and identified five robust apteronotid clades: (i) Sternarchorhamphus+Orthosternarchus, (ii) Adontosternarchus, (iii) Apteronotus+Parapteronotus, (iv) Sternarchorhynchus, and (v) a large clade including Porotergus, 'Apteronotus', Compsaraia, Sternarchogiton, Sternarchella, and Magosternarchus. We analyzed novel chirp recordings from two apteronotid species (Orthosternarchus tamandua and Sternarchorhynchus mormyrus), and combined data from these species with that from previously recorded species in our phylogenetic analyses. Some signal parameters in O. tamandua were plesiomorphic (e.g., low frequency EODs and chirps with little frequency modulation that nevertheless interrupt the EOD), suggesting that ultra-high frequency EODs and "big" chirps evolved after apteronotids diverged from other gymnotiforms. In contrast to previous studies, our PGLS analyses using the new phylogeny indicated the presence of phylogenetic signals in the relationships between some EOD and chirp parameters. The ASR demonstrated that most EOD and chirp parameters are evolutionarily labile and have often diversified even among closely related species.

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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.(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.(AU)

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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)

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