Nathan K. Lujan

Balancing hydropower and biodiversity in the Amazon, Congo, and Mekong

Basin-scale planning is needed to minimize impacts in mega-diverse rivers The worlds most biodiverse river basins—the Amazon, Congo, and Mekong—are experiencing an unprecedented boom in construction of hydropower dams. These projects address important energy needs, but advocates often overestimate economic benefits and underestimate far-reaching effects on biodiversity and critically important fisheries. Powerful new analytical tools and high-resolution environmental data can clarify trade-offs between engineering and environmental goals and can enable governments and funding institutions to compare alternative sites for dam building. Current site-specific assessment protocols largely ignore cumulative impacts on hydrology and ecosystem services as ever more dams are constructed within a watershed (1). To achieve true sustainability, assessments of new projects must go beyond local impacts by accounting for synergies with existing dams, as well as land cover changes and likely climatic shifts (2, 3). We call for more sophisticated and holistic hydropower planning, including validation of technologies intended to mitigate environmental impacts. Should anything less be required when tampering with the worlds great river ecosystems?

Morphological and functional diversity of the mandible in suckermouth armored catfishes (Siluriformes: Loricariidae)

We examined the mandibles of 377 individuals representing 25 species, 12 genera, 5 tribes, and 2 subfamilies of the Loricariidae, a species‐rich radiation of detritivorous–herbivorous neotropical freshwater fishes distinguished by having a ventral oral disk and jaws specialized for surface attachment and benthic feeding. Loricariid mandibles are transversely oriented and bilaterally independent, each rotating predominantly around its long axis, although rotational axes likely vary with mandibular geometry. On each mandible, we measured three traditional and three novel morphological parameters chosen primarily for their functional relevance. Five parameters were linear distances and three of these were analogous to traditional teleost in‐ and out‐levers for mandibular adduction. The sixth parameter was insertion area of the combined adductor mandibulae muscle (AMarea), which correlated with adductor mandibulae volume across a subset of taxa and is interpreted as being proportional to maximum force deliverable to the mandible. Multivariate analysis revealed distributions of phylogenetically diagnosed taxonomic groupings in mandibular morphospace that are consistent with an evolutionary pattern of basal niche conservatism giving rise to multiple adaptive radiations within nested clades. Correspondence between mandibular geometry and function was explored using a 3D model of spatial relationships among measured parameters, potential forces, and axes of rotation. By combining the model with known loricariid jaw kinematics, we developed explicit hypotheses for how individual parameters might relate to each other during kinesis. We hypothesize that the ratio [AMarea/tooth row length2] predicts interspecific variation in the magnitude of force entering the mandible per unit of substrate contacted during feeding. Other newly proposed metrics are hypothesized to predict variation in aspects of mandibular mechanical advantage that may be specific to Loricariidae and perhaps shared with other herbivorous and detritivorous fishes. 2011.

Trophic diversity in the evolution and community assembly of loricariid catfishes

BackgroundThe Neotropical catfish family Loricariidae contains over 830 species that display extraordinary variation in jaw morphologies but nonetheless reveal little interspecific variation from a generalized diet of detritus and algae. To investigate this paradox, we collected δ13C and δ15N stable isotope signatures from 649 specimens representing 32 loricariid genera and 82 species from 19 local assemblages distributed across South America. We calculated vectors representing the distance and direction of each specimen relative to the δ15N/δ13C centroid for its local assemblage, and then examined the evolutionary diversification of loricariids across assemblage isotope niche space by regressing the mean vector for each genus in each assemblage onto a phylogeny reconstructed from osteological characters.ResultsLoricariids displayed a total range of δ15N assemblage centroid deviation spanning 4.9‰, which is within the tissue–diet discrimination range known for Loricariidae, indicating that they feed at a similar trophic level and that δ15N largely reflects differences in their dietary protein content. Total range of δ13C deviation spanned 7.4‰, which is less than the minimum range reported for neotropical river fish communities, suggesting that loricariids selectively assimilate a restricted subset of the full basal resource spectrum available to fishes. Phylogenetic regression of assemblage centroid-standardized vectors for δ15N and δ13C revealed that loricariid genera with allopatric distributions in disjunct river basins partition basal resources in an evolutionarily conserved manner concordant with patterns of jaw morphological specialization and with evolutionary diversification via ecological radiation.ConclusionsTrophic partitioning along elemental/nutritional gradients may provide an important mechanism of dietary segregation and evolutionary diversification among loricariids and perhaps other taxonomic groups of apparently generalist detritivores and herbivores. Evolutionary patterns among the Loricariidae show a high degree of trophic niche conservatism, indicating that evolutionary lineage affiliation can be a strong predictor of how basal consumers segregate trophic niche space.

Revision of Panaque (Panaque), with Descriptions of Three New Species from the Amazon Basin (Siluriformes, Loricariidae)

Abstract The Panaque nigrolineatus group (subgenus Panaque) is revised; three nominal species—P. cochliodon, P. nigrolineatus, and P. suttonorum—are redescribed and three new species are described. Panaque armbrusteri, new species, is widespread in the Tapajós River and its tributaries in Brazil and is distinguished by having a supraoccipital hump, higher numbers of jaw teeth and an ontogenetic increase in interpremaxillary and intermandibular tooth-row angles, relatively short paired-fin spines, and dorsal margin of infraorbital six flared laterally. Panaque schaeferi, new species, is widespread in main-channel habitats of the upper Amazon (Solimões) River basin in Brazil and Peru; it is distinguished by having a coloration consisting of dark or faded black spots evenly distributed on a pale gray to brown base, and by its large adult body size (>570 mm SL). Panaque titan, new species, is distributed in larger, lowland to piedmont rivers of the Napo River basin in Ecuador, and is distinguished by having a postorbital pterotic region bulged beyond the ventral pterotic margin, coloration consisting of irregular and widely spaced dark gray to brown stripes on light brown to tan base, and large adult body size (>390 mm SL). A relatively large pterotic, indicative of an enlarged gas bladder and gas bladder capsule, and allometric increases in tooth number are hypothesized to be synapomorphies uniting members of the subgenus Panaque.

Microanatomy of the paired-fin pads of ostariophysan fishes (Teleostei: Ostariophysi).

Members of the teleost superorder Ostariophysi dominate freshwater habitats on all continents except Antarctica and Australia. Obligate benthic and rheophilic taxa from four different orders of the Ostariophysi (Gonorynchiformes, Cypriniformes, Characiformes, and Siluriformes) frequently exhibit thickened pads of skin along the ventral surface of the anteriormost ray or rays of horizontally orientated paired (pectoral and pelvic) fins. Such paired‐fin pads, though convergent, are externally homogenous across ostariophysan groups (particularly nonsiluriform taxa) and have been considered previously to be the result of epidermal modification. Histological examination of the pectoral and/or pelvic fins of 44 species of ostariophysans (including members of the Gonorynchiforms, Cypriniformes, Characiformes, and Siluriformes) revealed a tremendous and previously unrecognized diversity in the cellular arrangement of the skin layers (epidermis and subdermis) contributing to the paired‐fin pads. Three types of paired‐fin pads (Types 1–3) are identified in nonsiluriform ostariophysan fishes, based on differences in the cellular arrangement of the epidermis and subdermis. The paired‐fin pads of siluriforms may or may not exhibit a deep series of ridges and grooves across the surface. Two distinct patterns of unculus producing cells are identified in the epidermis of the paired‐fin pads of siluriforms, one of which is characterized by distinct bands of keratinization throughout the epidermis and is described in Amphilius platychir (Amphiliidae) for the first time. General histological comparisons between the paired fins of benthic and rheophilic ostariophysan and nonostariophysan percomorph fishes are provided, and the possible function(s) of the paired‐fin pads of ostariophysan fish are discussed. J. Morphol. 2012.

A New Black Baryancistrus with Blue Sheen from the Upper Orinoco (Siluriformes: Loricariidae)

Abstract Baryancistrus beggini, new species, is described from the upper Río Orinoco and lower portions of its tributaries, the Río Guaviare in Colombia and Río Ventuari in Venezuela. Baryancistrus beggini is unique within Hypostominae in having a uniformly dark black to brown base color with a blue sheen in life, and the first three to five plates of the midventral series strongly bent, forming a distinctive keel above the pectoral fins along each side of the body. It is further distinguished by having a naked abdomen, two to three symmetrical and ordered predorsal plate rows including the nuchal plate, and the last dorsal-fin ray adnate with adipose fin via a posterior membrane that extends beyond the preadipose plate up to half the length of the adipose-fin spine. Se describe una nueva especie, Baryancistrus beggini, del alto Río Orinoco y las partes bajas de sus afluentes: el río Guaviare en Colombia, y el río Ventuari en Venezuela. Baryancistrus beggini es la única especie entre los Hypostominae que presenta fondo negro oscuro a marrón sin marcas, con brillo azuloso en ejemplares vivos. Las primeras tres a cinco placas de la serie medioventral están fuertemente dobladas, formando una quilla notable por encima de las aletas pectorales en cada lado del cuerpo. Baryancistrus beggini se distingue también por tener el abdomen desnudo, dos o tres hileras de placas predorsales simétricas y ordenadas (incluyendo la placa nucal) y el último radio de la aleta dorsal adherido a la adiposa a través de una membrana que se extiende posteriormente, sobrepasando la placa preadiposa y llegando hasta la mitad de la espina adiposa.

Four New Hypancistrus (Siluriformes: Loricariidae) from Amazonas, Venezuela

Abstract Hypancistrus contradens, H. debilittera, H. furunculus, and H. lunaorum are described based on specimens from the upper Río Orinoco of southern Venezuela. Hypancistrus furunculus differs from other Hypancistrus based on color pattern: distinct dark oblique stripes ending at posterior insertion of dorsal fin and vertical bands in caudal fin (vs. oblique stripes ending at end of caudal fin in H. zebra and thin, indistinct, light-colored bands and vermiculations on a dark background in H. debilittera) and color pattern dark with white spots in H. contradens, H. inspector, and H. lunaorum. Hypancistrus contradens and H. lunaorum differ from H. inspector by having the dorsal fin reaching the adipose fin when adpressed (vs. not reaching), having spots on the head the same size as the body or spots absent (vs. spots smaller on head) and by usually having 22–23 mid-ventral plates (vs. 24); and from H. debilittera, H. furunculus, and H. zebra by lacking bars, saddles, or stripes on the body and bands in the fins. Hypancistrus lunaorum differs from H. contradens by having white spots on the body smaller than nasal aperture diameter (vs. white spots larger than the nasal aperture diameter). Se describen como especies nuevas a Hypancistrus contradens, H. debilittera, H. furunculus, e H. lunaorum sobre la base de especímenes provenientes de la cuenca alta del río Orinoco en el sur de Venezuela. Hypancistrus furunculus difiere de todas las demás especies de Hypancistrus por su patrón de coloración: barras oscuras oblicuas en el cuerpo que terminan al nivel del punto posterior de la base de la aleta dorsal y bandas verticales en la aleta caudal (vs. barras oblicuas oscuras terminando en el borde posterior de la aleta caudal en H. zebra y barras delgadas, indistintas y de color claro con manchas iregulares vermiformes sobre un color base oscuro en H. debilittera) y patrón de coloración con puntos blancos en H. contradens, H. inspector, e H. lunaorum. Hypancistrus contradens e H. lunaorum difieren de H. inspector en que la aleta dorsal alcanza la aleta adiposa cuando esta plegada contra el cuerpo (vs. aleta dorsal que no alcanza la adiposa), los puntos de la cabeza son del mismo tamaño de los puntos del cuerpo, o carece de puntos (vs. puntos de la cabeza mas pequeños que los puntos del cuerpo) y en tener usualmente 22–23 placas medioventrales (vs. 24); estas especies difieren de H. debilittera, H. furunculus, e H. zebra en que tienen barras, manchas en forma de silla de montar o franjas en el cuerpo y bandas en las aletas. Hypancistrus lunaorum difiere de H. contradens en que los puntos blancos del cuerpo son más pequeños que el diámetro de la apertura nasal (vs. puntos blancos más grandes que el diámetro de la apertura nasal).

Description of a new Lithoxus (Siluriformes: Loricariidae) from the Guayana Highlands with a discussion of Guiana Shield biogeography

Lithoxus jantjae, new species, is described from above Tencua Falls in headwaters of the Ventuari River, a white- to clearwater river flowing west from the Maigualida and Parima mountains in the Guayana Highlands of southern Venezuela. Lithoxus jantjae represents a nearly 600 km westward range expansion for a genus historically known only from Guyana, Suriname, French Guiana, and Brazil. Lithoxus jantjae shares with other species of Lithoxus a dorsoventrally depressed body and a large, papilose oral disk with small toothcups and few teeth. It can be distinguished from congeners by a unique combination of characters including 12 branched caudal-fin rays, medial premaxillary tooth cusps enlarged, and a convex posterior margin of the adipose-fin membrane. With the discovery of L. jantjae, Lithoxus becomes the most recent example of a growing list of rheophilic loricariid genera with disjunct distributions on east and west sides of the Guayana Highlands. A biogeographic hypothesis relying on the existence of a proto-Berbice River uniting the southern Guayana Highlands with rivers of the central Guiana Shield is advanced to partially explain the modern distribution of these species.

Evolution of nonspectral rhodopsin function at high altitudes

Significance Protein evolution in response to different environments has long been of interest to both evolutionary biologists and biochemists. High-altitude specialist catfishes in the Andes mountains offer an opportunity to examine the molecular adaptations accompanying adaptation to cold environments. Rhodopsins and other visual pigments form the first step in vision and have long been a model system for studying the molecular basis of sensory adaptations; however, many of these studies have focused solely on spectral shifts. Recent studies suggest that other aspects of function are as important for visual performance. We demonstrate that high-altitude amino acid variants significantly accelerate RH1 kinetics. These results suggest that the activity–stability trade-off characterized in cold-adapted enzymes also affects adaptation of signaling proteins through similar molecular mechanisms. High-altitude environments present a range of biochemical and physiological challenges for organisms through decreases in oxygen, pressure, and temperature relative to lowland habitats. Protein-level adaptations to hypoxic high-altitude conditions have been identified in multiple terrestrial endotherms; however, comparable adaptations in aquatic ectotherms, such as fishes, have not been as extensively characterized. In enzyme proteins, cold adaptation is attained through functional trade-offs between stability and activity, often mediated by substitutions outside the active site. Little is known whether signaling proteins [e.g., G protein-coupled receptors (GPCRs)] exhibit natural variation in response to cold temperatures. Rhodopsin (RH1), the temperature-sensitive visual pigment mediating dim-light vision, offers an opportunity to enhance our understanding of thermal adaptation in a model GPCR. Here, we investigate the evolution of rhodopsin function in an Andean mountain catfish system spanning a range of elevations. Using molecular evolutionary analyses and site-directed mutagenesis experiments, we provide evidence for cold adaptation in RH1. We find that unique amino acid substitutions occur at sites under positive selection in high-altitude catfishes, located at opposite ends of the RH1 intramolecular hydrogen-bonding network. Natural high-altitude variants introduced into these sites via mutagenesis have limited effects on spectral tuning, yet decrease the stability of dark-state and light-activated rhodopsin, accelerating the decay of ligand-bound forms. As found in cold-adapted enzymes, this phenotype likely compensates for a cold-induced decrease in kinetic rates—properties of rhodopsin that mediate rod sensitivity and visual performance. Our results support a role for natural variation in enhancing the performance of GPCRs in response to cold temperatures.

Two New Genera and Species of Ancistrini (Siluriformes: Loricariidae) from the Western Guiana Shield

Abstract Two new ancistrin genera and species are described from main channels and tributaries of the upper Orinoco River in Amazonas, Venezuela. Micracanthicus vandragti is black with white spots and distinguished by its small body-size, large gas-bladder capsules, and highly protrusible mandibles with short tooth cups and five to eight long teeth per tooth cup. The known range of Micracanthicus vandragti is restricted to the lower Ventuari River and portions of the Orinoco River near its rocky, anastomose confluence with the Ventuari River. Soromonichthys stearleyi is green with small yellow-gold spots on the head and thin vertical bars on the body and has long dentary and premaxillary tooth cups with 39–69 teeth per tooth cup. It is distinguished by its coloration and by its unique pattern of plate loss on the snout: plates absent from mesethmoid surface and anteriormost margin of snout. Soromonichthys stearleyi is known only from Soromoni Creek, a northern tributary of the upper Orinoco draining southern slopes of Mount Duida.