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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 associated with the human disease-associated substitution are likely 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.

Atypical fish diversity gradients suggest a recent formation of the Amazon system such as we know it today., Using the most comprehensive fish occurrence database, we evaluated the importance of ecological and historical drivers in diversity patterns of subdrainage basins across the Amazon system. Linear models reveal the influence of climatic conditions, habitat size and sub-basin isolation on species diversity. Unexpectedly, the species richness model also highlighted a negative upriver-downriver gradient, contrary to predictions of increasing richness at more downriver locations along fluvial gradients. This reverse gradient may be linked to the history of the Amazon drainage network, which, after isolation as western and eastern basins throughout the Miocene, only began flowing eastward 1–9 million years (Ma) ago. Our results suggest that the main center of fish diversity was located westward, with fish dispersal progressing eastward after the basins were united and the Amazon River assumed its modern course toward the Atlantic. This dispersal process seems not yet achieved, suggesting a recent formation of the current Amazon system.

The Cusiana River sub-basin has been identified as a priority conservation area in the Orinoco region in Colombia due to its high species diversity. This study presents an updated checklist and identification key for fishes of the Cusiana River sub-basin. The checklist was assembled through direct examination of specimens deposited in the main Colombian ichthyological collections. A total of 2020 lots from 167 different localities from the Cusiana River sub-basin were examined and ranged from 153 to 2970 m in elevation. The highest number of records were from the piedmont region (1091, 54.0 %), followed by the Llanos (878, 43.5 %) and Andean (51, 2.5 %). 241 species distributed in 9 orders, 40 families, and 158 genera were found. The fish species richness observed (241), represents 77.7 % of the 314 estimated species (95 % CI=276.1–394.8). The use of databases to develop lists of fish species is not entirely reliable; therefore taxonomic verification of specimens in collections is essential. The results will facilitate comparisons with other sub-basins of the Orinoquia, which are not categorized as areas of importance for conservation in Colombia.

Key to the species of Chaetostoma from the Orinoco River Basin in Colombia Photographs illustrating the characters of interest in the present key are available along with dorsal, lateral and ventral overall views for each of the species found in the Colombian Orinoco drainage, as well as additional materials are available at https://github.com/gaballench/Cjoropo. 1 a. Cheek odontodes straight; parieto-supraoccipital excrescence absent............................................ 2 1 b. Cheek odontodes curved, parieto-supraoccipital excrescence present............................................ 3 2 a. Snout covered with plates; light spots present on head................................... Chaetostoma platyrhynchus 2 b. Snout naked; light spots sometimes present on head, body, pectoral and pelvic fins, dorsal fin always with light spots........................................................................................... Chaetostoma dorsale 3 a. Spots present only on head and area surrounding dorsal-fin base; dorsal, pectoral, pelvic and anal fins with dark bands; sexual dimorphism in the anal fin where males have the second unbranched anal-fin ray elongated........ Chaetostoma formosae 3 b. Spots present on head and body; dorsal, pectoral, pelvic and anal fins with spots, sexual dimorphism in the anal fin absent................................................................................... Chaetostoma joropo n. sp.

Chaetostoma joropo, new species (Fig. 1, Table 1) Chaetostoma milesi (non Fowler, 1941) — (Lasso et al. 2004; Maldonado-Ocampo et al. 2008, 2013; Ortega-Lara et al. 2011; Urbano-Bonilla et al. 2009, 2014) [In checklists].— Zamudio et al. (2008) [Trophic ecology].—(Rodríguez-Olarte et al. 2011) [Basin-scale records within biogeographic analysis including C. milesi as present in both Magdalena-Cauca and Orinoco drainages] Holotype. MPUJ 7197, male, 108.8 mm SL, Colombia, Meta, Mesetas, Resevera, Guaviare, río Güejar, upper río Guaviare basin, Orinoco River Basin, coll. J. A. Maldonado-Ocampo et al., 8 -Dec- 2013. Paratypes. All from Colombia. ICNMHN 1795, 13, 60.8 – 105.6 mm SL, Meta, La Macarena, río Güejar, no coordinates available, coll. F. Jiménez-Segura et al., 1 -Jan- 1992; MPUJ 7198, 34, 85.7 – 31.0 mm SL, collected with the holotype; MPUJ 7201, 3, 82.4–99.6 mm SL, Casanare, Tauramena, Meta, río Cusiana, 5 °00' 0.13 "N, 72 ° 40 ' 0.5 "W, coll. S. Prada-Pedreros, 6 -Jul- 2014; MPUJ 7202, 5, 25.0 – 97.8 mm LS, Casanare, Tauramena, Meta, río Cusiana, 5 ° 01' 21.7 "N, 72 ° 41 ' 27.8 "W, coll. S. Prada-Pedreros, 29 -Sep- 2012; MPUJ 7203, 19, 31.0– 124.7 mm LS, same collector and locality data as MPUJ 7201, 11-Dec- 2012; MPUJ 7204, 32, 12.5– 90 mm SL, same collector and locality data as MPUJ 7201, 11-Feb- 2013; MPUJ 7205, 182, 15 – 97.2 mm SL, same collector and locality data as MPUJ 7202, 10-Feb- 2013; MPUJ 7206, 13, 37.0– 72.8 mm SL, Casanare, Tauramena, Meta, río Caja, 5 ° 10 ' 11.8 "N, 72 ° 42 ' 17.9 "W, coll. S. Prada-Pedreros, 8 -Feb- 2013. Non-type specimens. MPUJ 7199, 37, 72.7 – 27.6 mm SL, Meta, Vista Hermosa, Vereda Puerto Lucas, río Güejar, 3 ° 1 ' 37.35 "N, 73 ° 50 ' 24.70 "W, coll. J. A. Maldonado-Ocampo, 7 -Dec- 2013; MPUJ 7200, 1, 36.1 mm SL, Meta, Vista Hermosa, Caserío Maracaibo, Guaviare, Quebrada Sardinata, 3 ° 20 ' 39.91 "N, 73 ° 20 ' 39.91 "W, coll. J. A. Maldonado-Ocampo, 7 -Dec- 2013; MPUJ 7305, 2, 82.1–86.2 mm Sl, Arauca, Tame, Vereda el Banco Purare, río Purare, 6 ° 15 ' 51 "N, 71 ° 51 ' 38.8 "W, coll. J. Zamudio, 9 -May- 2015; MPUJ 7306, 1, 92.8 SL mm, Arauca, Tame, Vereda el Banco Purare, río Tocoragua, 6 ° 16 ' 52 "N, 71 ° 52 ' 23.7 "W, coll. J. Zamudio, 9 -May- 2015. Diagnosis. Chaetostoma joropo differs from all the species currently known to be present in the Orinoco River Basin by having dark spots on head and body as well as on dorsal, pectoral and pelvic fins (vs. dark spots present only on head in Chaetostoma formosae, light dots on head in C. dorsale and C. platyrhynchus, dark spots absent in C. vasquezi). It also differs as follows: from Chaetostoma formosae in the absence of sexual dimorphism in the length of the second unbranched ray of the anal fin (vs. dimorphism present); from Chaetostoma dorsale and C. platyrhynchus by the presence of recurved cheek odontodes and a parieto-supraoccipital excrescence (vs. cheek odontodes straight and excrescence absent), and from Chaetostoma platyrhynchus in having a naked snout (vs. snout covered with plates). Only a few species of Chaetostoma present a color pattern consisting of spots on both the head and the body (C. anale, C. daidalmatos, C. lineopunctatum, C. milesi, C. strompoulos, C. trimaculineum and C. vagum, (Lujan et al. 2015 a; Salcedo 2006 b). Chaetostoma joropo differs from these species except C. daidalmatos by having spots on the body that are larger (in diameter) than the spaces separating them from neighboring spots(vs. space between spots larger or equal to spot diameter in C. anale, C. lineopunctatum, C. milesi, C. strompoulos, and C. vagum). Chaetostoma joropo differs from C. daidalmatos by having spots that are smaller than the orbital diameter (vs. spots larger than orbital diameter, (Salcedo 2006 b). Finally, Chaetostoma joropo differs from C. milesi as follows: by having the spots on the head more densely packed together, with the space between spots smaller than spot diameter (vs. spots less numerous and with space between spots larger than spot diameter in C. milesi); by having more spots on body that are better organized in longitudinal rows (vs. spots less numerous and scattered in C. milesi); by the presence of scattered, numerous spots on the dorsal fin (vs. less numerous and always positioned anterior to each branched fin ray in C. milesi); by having a uniform black coloration on the dorsal surface of the pectoral spine (vs. with longitudinal row of spots on dorsal surface of pectoral spine in C. milesi); and by presenting undulated vertical bars on the caudal fin that transform progressively into spots (vs. caudal fin uniformly dark regardless of size in C. milesi). Description. Measurements presented in Table 1. A large-sized Chaetostoma, with largest examined specimen 124.7 mm SL (paratype male, MPUJ 7203). Head and body slightly depressed and wide. Dorsal profile of anterior portion of head in lateral view convex from unplated region of snout to vertical through posterior nares, then convex toward dorsal-fin insertion. Dorsal profile of body straight to slightly convex and concave from dorsal-fin insertion to caudal-fin origin. Ventral profile of head and body straight from snout tip to caudal peduncle. Interorbital area slightly convex. Dorsal surface of snout region convex. Head in dorsal view roundish or oval with irregular margin due to development of skin. Snout naked, covered by fleshy papillae and ridges. Anterior margin of plated portion of snout roughly V- or U-shaped, starting on snout midline and then extending posteriorly to dorsal margin of exposed portion of opercle forming ventral margin nearly parallel or slightly oblique to ventral head margin. Unplated snout region more extensive in mature males than in females. Parieto-supraoccipital dermal excrescence present. All lateral plate series other than ventral series complete from compound pterotic to caudal peduncle; ventral series incomplete anteriorly and beginning anterior to pelvic-fin insertion. Abdomen completely naked. First analfin pterygiophore not exposed. Median series with 23–25 plates (mode 24), showing individual and intraindividual variation. Hypertrophied cheek odontodes distally and strongly recurved, usually not surpassing posterior margin of exposed opercle when adpressed. Exposed portion of opercle roughly triangular in shape, weak mesial indentation evident externally where musculus dilatator operculi complex inserts onto opercle. Cheek plates not exposed. Fleshy ridge posterior to cheek odontodes present, sometimes reaching ventral margin of exposed opercle dorsally when cheek odontodes adpressed. Frontal, infraorbital, nasal, exposed opercle, compound pterotic, sphenotic, and parieto-supraoccipital bones supporting odontodes. Odontodes present on exposed portion of opercle. Odontodes flat and sharp on lateral plates but flat and spatulate on area between orbit and naris, mesethmoidal region and dorsal surface of snout. Odontodes flat and spatulate on dorsal surface of dorsal spine and spinelet, adipose fin, and dorsal leading ray of caudal fin. Odontodes flat and spatulate on ventral and lateral surfaces of pectoral and pelvic fin, and on anterior surface of anal fin and ventral leading ray of caudal fin. Hypertrophied pectoral-spine odontodes basally surrounded by fleshy collar and frequently with small posterior papilla. Remaining odontodes developing directly on plates and rays without associated papillary soft tissues. All plates of lateral series with largest odontodes on posterior margin and shorter ones on plate surface. Posterior tip of dorsal-fin reaching or surpassing origin of adipose spine when adpressed. Dorsal spine not elongate or extending beyond margin of remainder of fin. Dorsal spine stiff basally but flexible distally. Distal margin of dorsal fin slightly convex. Margin of dorsal-fin spinelet moderately acute, bearing odontodes. Dorsal-fin spinelet exposed in mature specimens, regardless of sexual condition. Dorsal-fin lock functional. Dorsal-fin ray formula ii, 8. Adipose spine preceded by one unpaired plate. Dorsal procurrent caudal-fin rays 5–6 (mode 5) and ventral procurrent rays 4–5 (mode 4). Caudal fin oblique with lower portion longer than upper portion; dorsal and ventral unbranched rays longer than branched rays; distal margin emarginate. Caudal-fin base covered by acute platelets variable in number. Caudal-fin ray formula i, 14,i (i, 13,i in one individual). Anal-fin base short. Anal-fin ray formula ii, 3–4 (mode ii, 4). Pectoral spine with short and thick hypertrophied odontodes on tip but with distinct dorsal row of odontodes throughout midline, showing sexual variation in odontode curvature. Tip of pectoral spine when adpressed reaching to level of vent in mature specimens. Posterior margin of pectoral fin straight to slightly convex. Tip of adpressed pectoral spine reaching from one-third to middle of leading pelvic-fin ray length. Pectoral-fin ray formula i, 6. Tip of pectoral spine when adpressed reaching or sometimes surpassing level of vent in mature specimens. Odontodes on dorsal surface of pelvic-fin rays not hypertrophied and not protruding from skin in both males and females. Pelvic fin with variable distal margin from convex and round in females to strongly convex and angular in mature males. Pelvic-fin leading ray more than twice as thick as remaining rays. Pelvic-fin ray formula i, 5. Iris operculum present. Short, fleshy flap with round margin present between anterior and posterior nares, deeper mesially. Upper lip with multiple series of papillae, those proximate to mouth opening small and round, followed distally by larger and widely elongate ones. Lower lip with medium-sized round papillae anteriorly and smaller ones posteriorly, with smooth skin close to posterior margin of lip; border crenate. Maxillary barbels moderate in length, separate distally from lower lip. Lower lip basally fused up to one-third or even half of total barbel length in some individuals; fleshy ridge present dorsally almost over entire length of each barbel, also showing individual variation. Buccal papilla present at symphysis of premaxillae. Premaxillary ornamentation usually consisting of individual small papillae arranged transversely. Dentary ornamentation consisting of mesial transverse papillary ridge and secondary single papillae arranged lateral to main ridge. Jaws wide transversely. Posterior margin of premaxillae forming nearly straight line. Dentary wider than premaxilla. Both rami with nearly straight tooth cups only recurved on lateral margins. Tooth peduncle fairly long, narrow, and distally recurved. Cusps asymmetrically developed with lateral tooth cusp approximately one-half length of medial cusp. Dentary teeth 32–157, premaxillary teeth 24–128, showing increase with age. Coloration in alcohol. Overall body background grayish-green with black spots on head, fins and body. Head and dorsum with scattered black spots; lateral plates with dense and numerous dark spots, tending to become aligned in longitudinal rows posteriorly. Parieto-supraoccipital fleshy excrescence usually black, but sometimes less intensely pigmented. Pectoral, pelvic, dorsal, anal, and caudal fins with dusky membranes and scattered numerous spots. Pectoral spine with black pigment. Dorsal fin with basal anterior black spot between leading ray and first branched ray absent in contrast to presence in C. formosae. Anal fin with dark blotches, ill-defined and very few in number. Caudal fin with undulated bars on caudal fin that transform progressively into spots with age. Venter light, without dark pigment. Coloration in life. Specimens of Chaetostoma joropo show variation in color pattern ranging from yellowishgreen background coloration to grayish green; venter and preanal regions are in both cases lighter, and darker posterior to anal fin. Pattern also includes back spots on head, fins, dorsum and sides of body, in contrast to ventral portions other than on caudal peduncle that lack spots, with just few spots on postanal region. Interradial membranes share the same color as background pattern. Adults with longitudinal black stripe on pectoral spine extending from base to tip; in juveniles stripe proximally interrupted and consisting of spots (Figure 2). Ontogenetic variation. Chaetostoma joropo shows ontogenetic variation in color pattern and development of pelvic-fin distal margin. Juveniles present an almost plain color pattern with few large blotches that become progressively smaller until transformation into more numerous spots better organized in rows (Figure 3). Both male and female juveniles have a more narrow naked area on snout that becomes wider in adults, further showing sexual dimorphism between males and females. Supraoccipital excrescence more pronounced in juveniles than adults, probably as a consequence of thickening of dorsal skin in adults. Distal margin of pelvic fin in juveniles straight, becoming round in adults as observed in other species of Chaetostoma (e.g., C. milesi). Sexual variation. Mature males develop a fleshy dorsal ridge on the pelvic-fin leading ray, from insertion of fin to near the tip of ray; in contrast, females lack such condition. Mature males show a more extensive unplated portion of snout, whereas mature females show a more plated snout. Dorsal longitudinal single row presents acute recurved odontodes in mature males whereas mature females show more straight odontodes. Distal margin of pelvic fin convex and round in both sexes, but males usually have more developed pelvic fins than females. Males have a pointed and discrete genital papilla, that in females is a wide and pad-like papilla. The papillae in both sexes have a terminal aperture; however, once reaching maturity and when eggs are mature, females develop a swollen posterior portion, which makes the papilla appear to be directed towards the vent tube. Males are larger than females (largest male examined 124.7 mm SL vs. largest female examined 115.1 mm SL, both mature adults). Distribution. Chaetostoma joropo is present in piedmont rivers of the Orinoco River Basin in Colombia. Based on voucher specimens we record its presence in the Casanare, Meta and Guaviare drainages, from Vista Hermosa in the Departamento de Meta to the south to the río Tocoragua in the municipality of Tame, Departamento de Arauca to the north (Figure 4). The distribution of this species coincides with that of C. dorsale, C. formosae and Dolichancistrus fuesslii in the Orinoco drainage (Ballen & Vari 2012; Ballen 2011). Ecological notes. Chaetostoma joropo shows preference for rocky substrates, shallow (0.20–0.55 m) but well oxygenated water (6.1–9.5 mg /L), and slightly basic pH (7.1–8.6); conductivity (10.4 –258.0 µS) as well as temperature (21–30 °C) are variable (Figure 5). This species occasionally feeds on insect larvae (Diptera), and are mostly algivores (e.g., Aulacoseira sp., Cymbella sp., Fragilaria sp., Gyrosigma sp., Navicula sp., Oscillatoria sp., Pinnularia sp., Surirella sp., Spirogyra sp., Synedra sp., Tabellaria sp.). Chaetostoma joropo occurs with other species of the same family (Chaetostoma dorsale, C. formosae, C. platyrhynchus, Panaqolus maccus and Lasiancistrus tentaculatus) as well as crenuchids (Characidium gr. boavistae, C. chupa and C. cf. steindachneri), parodontids (Parodon apolinari), characids (Bryconamericus cismontanus, B. cristiani, Creagrutus bolivari, C. taphorni, C. maculosus, Hemibrycon metae and Salminus hilarii), heptapterids (Cetopsorhamdia orinoco, Phenacorhamdia macarenensis and Rhamdia quelen), cetopsids (Cetopsis orinoco and C. coecutiens), aspredinids (Hoplomyzon sexpapilostoma), trichomycterids (Trichomycterus knerii, Ochmacanthus alternus, Schultzichthys bondi and S. gracilis), apteronotids (Apteronotus albifrons), and cichlids (Crenicichla saxatilis). Etymology. The word joropo refers to a collection of musical styles that originated in the Llanos region of the Orinoco River Basin. It is one of the most characteristic cultural expressions among the criollos, the people who live in the Llanos Orientales. This name recognizes the importance and beauty of this region through one of its most iconic cultural expressions, which does not account for political boundaries and promotes brotherhood among the people of Colombia and Venezuela. It is used as a noun in apposition.

The present study describes ecological aspects of Lebiasina erythrinoides; 200 individuals were sampled throughout an annual hydrological cycle from October 2008 to September 2009 in La Calaboza stream, a Piedmont tributary of the Rio Cravo Sur. The studied population had more females than males (1.5:1) and preferred habitats dominated by shoreline vegetation and rocky substrates. Prior to reproductive events, individuals presented an increase in the condition factor (K) and the gonosomatic index (GSI). On average, 648.8 oocytes are discharged twice a year: at the beginning of the rainy season, and during falling water phase. The mean sizes at sexual maturity found for females were 73.5 mm standard length (SL) and for males 70 mm SL. Rounding up, an average minimum size of capture of 75 mm SL is proposed. Most specimens of the population (65 %) were found to be maturing or mature (stages II and III), 28.5 % immature (stage I), 5.0 % in post reproduction stage V, and 1.5 % in reproductive phase (IV). Results suggest this species is omnivorous with a preference for invertebrates (IRI = 41.2 %) and vegetal material (IRI = 27.8 %), but also includes a variety of other items. The values of the diet are correlated with hydrological cycle and size. El presente estudio describe aspectos ecológicos de Lebiasina erythrinoides. Se muestrearon 200 individuos a lo largo del ciclo hidrológico anual, de Octubre de 2008 a Septiembre de 2009, en la quebrada La Calaboza, un tributario de piedemonte del Río Cravo Sur. La población estudiada presentó más hembras que machos (1.5:1) y prefirió hábitats dominados por vegetación riparia y sustratos rocosos. Antes de los eventos reproductivos, los individuos presentaron un incremento en el factor de condición (K) y en el índice gonadosomático (GSI). En promedio, se descargaron 648.8 oocitos dos veces en el año: al inicio de la estación lluviosa y durante la fase de descenso de las aguas. Los tamaños promedio de las hembras en madurez sexual fueron de 73.5 mm de longitud estándar (SL), y de los machos, 70 mm SL. De acuerdo con estas cifras, se propone un tamaño mínimo de captura de 75 mm SL. La mayor parte de especímenes de la población (65 %) se encontró en proceso de maduración o de madurez (estadios II y III), 28.5 % en estado inmaduro (estadio I), 5.0 % en estado post-reproductivo (V) y 1.5 % en fase reproductiva (V). Los resultados sugieren que esta especie es omnívora: prefiere invertebrados (IRI = 41.2 %) y material vegetal (IRI = 27.8 %), pero su dieta incluye también variedad de otros ítems. Los valores de la dieta se correlacionan con el ciclo hidrológico y con el tamaño. O presente estudo descreve aspectos ecológicos de Lebiasina erythrinoides. Foram coletados 200 indivíduos ao longo de um ciclo hidrológico anual, entre Outubro de 2008 e Setembro de 2009 no riacho La Calaboza, um afluente do rio Cravo Sur. A populacho estudada possuía mais fèmeas que machos (1.5:1) e preferiam habitats dominados por vegetalo costeira e substratos rochosos. Prèvio aos eventos reprodutivos, os individuos presentaram um aumento do fator de condicio (K) e do índice gonadosomatico (GSI). Em mèdia, 648.8 ovócitos são desovados duas vezes ao ano: no inicio do período chuvoso, e durante a descida das águas. O tamanho mèdio encontrado para as fèmeas na maturidade sexual foi de 73.5 mm comprimento padrão (SL), e para os machos foi de 70 mm SL. Considerando os valores encontrados, se propoe que o tamanho mínimo de captura seja de 75 mm SL. A maioria dos espècimes da populacho estudada (65 %) se encontrava nos estágios de maturação ou maduros (Estágios II e III), 28.5 % de imaturos (I), 5.0 % em estágio pós-reprodução (V) e 1.5 % em fase reprodutiva (IV). Os resultados sugerem que a espécie é omnívora, com uma preferencia por invertebrados (IRI = 41.2 %) e material vegetal (IRI = 27.8 %), mas também se inclui uma variedade de outros itens. Os valores da dieta estão correlacionados com o ciclo hidrológico e tamanho.