Reproduction and Feeding of the Electric Fish <i>Brachyhypopomus gauderio</i> (Gymnotiformes: Hypopomidae) and the Discussion of a Life History Pattern for Gymnotiforms from High Latitudes

<div><p>The reproductive biology and feeding habits of the electric fish <i>Brachyhypopomus gauderio</i> were studied. The species has seasonal reproductive behavior, with breeding occurring during the Southern Hemisphere spring and summer, and having a positive relation with the photoperiod variation. <i>Brachyhypopomus gauderio</i> was defined as a fractional spawner, with low relative fecundity and high first maturation size. Sexual dimorphism was registered, males undergoing hypertrophy of the distal portion of caudal filament. The results on reproductive biology herein obtained are in agreement with data concerning gymnotiforms from Southern Brazil and Uruguay, pointing to an ecological pattern for the species from high latitudes, differing from species with tropical distribution. According to the analysis of the food items, <i>B</i>. <i>gauderio</i> feed mainly on autochthonous insects, likewise the other gymnotiforms previously investigated, leading to conclude that there is no variation on the diet of the species of the order related to climatic conditions or even to habitat of occurrence.</p></div

Phylogenetic Systematics, Biogeography, and Ecology of the Electric Fish Genus <i>Brachyhypopomus</i> (Ostariophysi: Gymnotiformes)

<div><p>A species-level phylogenetic reconstruction of the Neotropical bluntnose knifefish genus <i>Brachyhypopomus</i> (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 <i>Brachyhypopomus</i> 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 <i>Microsternarchus</i> + <i>Racenisia</i> in a position deeply nested within <i>Brachyhypopomus</i>. Consideration of geographical distribution in light of the total evidence phylogeny indicates an origin for <i>Brachyhypopomus</i> 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 <i>Brachyhypopomus</i> 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 <i>Brachyhypopomus</i> are eurytopic with respect to habitat occupancy and these generally exhibit wider geographical ranges than stenotopic species.</p></div