The evolution of communication behavior, like that of all traits, is shaped both by external forces of natural and sexual selection and by internal forces of development and physiology. Complexity in both the function and production mechanisms of communication signals makes them a powerful model for understanding evolutionary interactions within and across levels of biological organization (Ryan, 2005).Electrocommunication in weakly electric fish is an outstanding model for integrating mechanistic and historical biology (sensu Autumn et al., 2002) because these behaviors are diverse across species, are easily recorded and analyzed, and are controlled by a well-characterized neural circuit. The family Apteronotidae is particularly well-suited for a comparative approach because it has the highest species diversity among Neotropical electric fish (Crampton and Albert, 2006). Apteronotids continuously emit a quasi-sinusoidal voltage signal or electric organ discharge (EOD) that has two functions. Nearby objects locally distort the electric field generated by the EOD, and by detecting these distortions with their electroreceptors, fish can electrolocate. The fish can also use their EODs to communicate by detecting the interactions of their own EOD with those of other fish. Individual apteronotid fish maintain an extremely stable EOD frequency (EODf) (Bullock, 1970;Moortgat et al., 1998) and waveform (Rasnow and Bower, 1996). In addition to using the baseline EOD frequency and waveform as communication signals, fish also modulate the frequency and amplitude of the EOD during social interactions Electrocommunication signals in electric fish are diverse, easily recorded and have well-characterized neural control. Two signal features, the frequency and waveform of the electric organ discharge (EOD), vary widely across species. Modulations of the EOD (i.e. chirps and gradual frequency rises) also function as active communication signals during social interactions, but they have been studied in relatively few species. We compared the electrocommunication signals of 13 species in the largest gymnotiform family, Apteronotidae. Playback stimuli were used to elicit chirps and rises. We analyzed EOD frequency and waveform and the production and structure of chirps and rises. Species diversity in these signals was characterized with discriminant function analyses, and correlations between signal parameters were tested with phylogenetic comparative methods. Signals varied markedly across species and even between congeners and populations of the same species. Chirps and EODs were particularly evolutionarily labile, whereas rises differed little across species. Although all chirp parameters contributed to species differences in these signals, chirp amplitude modulation, frequency modulation (FM) and duration were particularly diverse. Within this diversity, however, interspecific correlations between chirp parameters suggest that mechanistic trade-offs may shape some aspects of signal evolution. In particular, a consistent trade-of...

The bluntnose knifefish genus Brachyhypopomus Mago-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 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 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

Neotropical electric knifefishes of the family Sternopygidae previously considered to represent a single relatively geographically widespread and morphologically variable species, Archolaemus blax, were analysed and found to represent a complex of five species, four of which are new to science. A fifth undescribed species from the Rio São Francisco basin outside the previous known range of the genus was identified. Recognized species of Archolaemus are: A. blax, previously thought to occur in the Rio Araguari, Rio Branco, Rio Tapajós, Rio Tocantins, and Rio Xingu, but which instead proved to be endemic to the Rio Tocantins; Archolaemus ferreirai sp. nov. from the Rio Mucajaí and Rio Uraricoera in the north‐eastern portions of the Amazon basin; Archolaemus janeae sp. nov. of the Rio Xingu and the upper Rio Tapajós, both southern tributaries of the mainstream Amazon; Archolaemus luciae sp. nov. of the Rio Trombetas, Rio Jari, and Rio Tapajós basins of the eastern Amazon, and the independent Rio Araguari draining into the Atlantic Ocean north of the mouth of the Amazon; Archolaemus orientalis sp. nov. of the São Francisco basin in eastern Brazil; and Archolaemus santosi sp. nov. of the Rio Jamari in the south‐western portion of the Amazon basin. The phylogenetic placements of Archolaemus and the recently described genus Japigny relative to the other members of the Eigenmanninae are discussed. A series of synapomorphies for Archolaemus are proposed and a hypothesis of the relationships within that genus is advanced. Rheophily of all members of Archolaemus is discussed, with the genus found to be the most specious clade within the Gymnotiformes living primarily in high‐energy settings. The reported anterior projection of the dentary teeth in A. blax was found to be a consequence of postmortem displacement.

Analysis of 88 characters of external and internal body systems yielded a phylogenetic reconstruction of the Neotropical electric knifefish genus Sternarchorhynchus (Apteronotidae; Gymnotiformes). The results support a hypothesis of Sternarchorhynchus as the sister group to Platyurosternarchus. A series of synapomorphies, many involving major innovations of the neurocranium, jaws, suspensorium, and associated systems that permit an unusual mode of grasp-suction feeding, support the monophyly of both genera. Synapomorphies largely resolve relationships within Sternarchorhynchus with basal nodes strongly supported by characters pertinent to prey capture and initial processing of food items. These possible key innovations may provide Sternarchorhynchus with a competitive advantage over other clades of the Apteronotidae and account for the species diversity of the genus in Neotropical rivers. Adaptive radiation in Sternarchorhynchus was analysed. Habitat preference transitions repeatedly occurred in the genus between deep-river channel dwelling species and rheophilic species with preferences for higher energy setting including rapids and swift-flowing fluviatile settings. Twenty-two species of Sternarchorhynchus are described as new based on samples that originated in the smaller rivers draining into the Golfo de Paria, the Marowijne and Essequibo River basins, the Río Orinoco and in particular the Amazon River basin. The 32 species in Sternarchorhynchus make it the most speciose genus in the Apteronotidae.No claim to original US government works. Journal compilation

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.

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.

A phylogenetic reconstruction of the Neotropical electric fish genus Hypopygus based on 47 parsimony-informative morphological characters is presented. A series of synapomorphies support the hypothesis of monophyly of Hypopygus, and partially resolve species-level relationships within the genus. Hypopygus species are recognized here as miniaturized fishes based on two criteria; first, a derived condition of diminutive body size, and; second, the presence of a suite of reductive morphological characters, including partial or total losses, simplifications, and reductions of the anal-fin rays, scales, cranial bones, and laterosensory canal system. Reductive characters associated with miniaturization comprise 45% of the total number of characters in the phylogenetic reconstruction of the genus. Miniaturization and reductive morphological evolution in Hypopygus are discussed here in the phylogenetic context. A taxonomic revision of Hypopygus is presented, in which five new species are described, two species previously assigned to the genus are redescribed, and a single known species of Stegostenopos is redescribed and included in Hypopygus as a junior synonym. Distribution maps and a key for all eight valid species of Hypopygus are provided, based on the examination of 5014 catalogued museum specimens.

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