Leandro M. Sousa

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?

Morphology of the Gas Bladder in Thorny Catfishes (Siluriformes: Doradidae)

ABSTRACT. The gross morphology of the gas bladder is described, illustrated, compared and categorized among 86 of 88 nominal valid and six undescribed species representing all 31 genera of Doradidae with comments on ontogenetic and taxonomic variation when observed. The putatively basal-most doradids exhibit an unmodified cordiform gas bladder. Derived taxa exhibit an impressive suite of modifications including the addition of a secondary bladder, pronounced reduction of the posterolateral chambers, internal trabeculae, associations with bony capsule-like expansions of the anterior (Weberian) vertebrae, and accessory diverticula varying widely in size, shape, abundance, and distribution, Intra-specific differences are minor, most often reflective of ontogenetic changes especially in large-size species, whereas inter-specific and inter-generic differences are significant, in many cases diagnostic, and suggestive of phylogenetic signal excepting instances of evident convergence such as gas bladder reduction in Rhynchodoras and all but one species of Leptodoras.

Description of two new species of Physopyxis and redescription of P. lyra (Siluriformes: Doradidae)

The genus and species Physopyxis lyra was originally described based on only one very distinctive specimen. Analysis of a larger number of specimens provided a more precise characterization of the genus and the type species. Additionally, two new species are described based on material already available in museums and new collections. Physopyxis lyra is characterized by having a well developed coracoid process with divergent tips, and only one series of spines on the lateral plates. Physopyxis ananas, new species, has a thin coracoid process, convergent, and more than one series of spines on the lateral plates. Physopyxis cristata, new species, is a slender species, characterized by an incomplete series of lateral plates and the presence of a middorsal series of spines formed by the tips of the vertebral neural spines. The poorly known geographic distribution of the genus Physopyxis is vastly enlarged to include various drainages of the Amazon and Essequibo basins.

Seasonal changes in the assembly mechanisms structuring tropical fish communities

Despite growing interest in trait-based approaches to community assembly, little attention has been given to seasonal variation in trait distribution patterns. Mobile animals can rapidly mediate influences of environmental factors and species interactions through dispersal, suggesting that the relative importance of different assembly mechanisms can vary over short time scales. This study analyzes seasonal changes in functional trait distributions of tropical fishes in the Xingu River, a major tributary of the Amazon with large predictable temporal variation in hydrologic conditions and species density. Comparison of observed functional diversity revealed that species within wet-season assemblages were more functionally similar than those in dry-season assemblages. Further, species within wet-season assemblages were more similar than random expectations based on null model predictions. Higher functional richness within dry season communities is consistent with increased niche complementarity during the period when fish densities are highest and biotic interactions should be stronger; however, null model tests suggest that stochastic factors or a combination of assembly mechanisms influence dry-season assemblages. These results demonstrate that the relative influence of community assembly mechanisms can vary seasonally in response to changing abiotic conditions, and suggest that studies attempting to infer a single dominant mechanism from functional patterns may overlook important aspects of the assembly process. During the prolonged flood pulse of the wet season, expanded habitat and lower densities of aquatic organisms likely reduce the influence of competition and predation. This temporal shift in the influence of different assembly mechanisms, rather than any single mechanism, may play a large role in maintaining the structure and diversity of tropical rivers and perhaps other dynamic and biodiverse systems.

A New Miniature Characid (Ostariophysi: Characiformes: Characidae), with Phylogenetic Position Inferred from Morphological and Molecular Data

Erythrocharax altipinnis is described from the Serra do Cachimbo, Pará, Brazil. The new taxon is distinguished from all of the Characidae genera by having the pelvic bones firmly attached through the isquiatic processes; a nearly triangular hiatus in the musculature covering the anterior chamber of the swim bladder between the first and second pleural ribs (pseudotympanum); the pedunculate, notably expanded and distally compressed teeth in both jaws; circumorbital series represented by antorbital and four infraorbital bones with laterosensory canals not enclosed; a single tooth row in the premaxillary with the teeth perfectly aligned and similar in shape and cusp number; the first three branched dorsal-fin rays distinctly elongate in males; a bright red adipose and caudal fins in life; a conspicuous dark midlateral stripe extending from the opercle to the tip of the median caudal-fin rays; and by the absence of a humeral spot. The phylogenetic position of the new taxon is discussed using morphological and molecular datasets, with conflicting results of both approaches discussed. Additionally, a summarized discussion on the current problems in the Characidae taxonomy is presented and the principal biases in the morphological dataset are also discussed.

Two new species of Hyphessobrycon (Characiformes: Characidae) from the headwaters of the Tapajós and Xingu River basins, Pará, Brazil

Two new species of Hyphessobrycon are described from the headwaters of the Tapajós and Xingu River basins, Pará, Brazil. Both new species can be distinguished from congeners by the presence of a vertically elongate humeral blotch, a conspicuous round to vertically oblong caudal-peduncle blotch not extending onto the distal portions of the middle caudal-fin rays, a conspicuous blotch on the central portion of the third infraorbital immediately ventral to the eye, the lack of a conspicuous longitudinal stripe and the lack of sexual dimorphism in the extension of the caudal-peduncle blotch. Hyphessobrycon delimai n. sp. can be distinguished from Hyphessobrycon krenakore n. sp. by the extent of the caudal-peduncle blotch which extends across most of the caudal-peduncle depth (v. restricted to the middle portion of the caudal peduncle), the presence of dark chromatophores uniformly scattered along the length of the interradial membranes of the dorsal, anal and caudal fins (v. concentrated on the distal one-half or one-fourth of the interradial membranes) and the absence of small bony processes on the pelvic and anal fins of mature males (v. small bony processes present).

Taxonomic Revision of the Genus Scorpiodoras (Siluriformes: Doradidae) with Resurrection of Scorpiodoras calderonensis and Description of a New Species

Three species of Scorpiodoras are recognized: S. calderonensis, S. heckelii, and S. liophysus; the latter species is described herein. Scorpiodoras calderonensis occurs in the upper Amazon basin, including the Solimões, Juruá, Japurá, and Tefé rivers. Its type locality, originally stated as “Calderón”, is elucidated as Tabatinga, Brazil. Scorpiodoras heckelii is the most widespread species, occurring in the Orinoco, Branco, Negro, and Amazonas rivers downstream of its confluence with Rio Negro. Scorpiodoras liophysus is only known from the middle Rio Madeira basin and presents a morphological feature unique within the genus: gas bladder without secondary bladder. An osteological description of the genus is provided, as well as redescriptions of S. calderonensis and S. heckelii. Additionally, a key allowing identification of the species is presented, as well as a biogeographic discussion. Três espécies de Scorpiodoras são reconhecidas: S. calderonensis, S. heckelii, e S. liophysus, esta última descrita aqui. Scorpiodoras calderonensis ocorre na bacia do alto rio Amazonas, incluindo os rios Solimões, Juruá, Japurá, e Tefé. Sua localidade tipo, originalmente descrita como “Calderón”, é elucidada como sendo Tabatinga, Brasil. Scorpiodoras heckelii é a espécie mais amplamente distribuída, ocorrendo nos rios Orenoco, Branco, Negro, e Amazonas abaixo de sua confluência com o rio Negro. Scorpiodoras liophysus é conhecido apenas do médio rio Madeira e apresenta uma característica única no gênero: bexiga natatória sem bexiga secundária. Uma descrição osteológica do gênero é feita, assim como redescrição de S. calderonensis e S. heckelii. Adicionalmente, uma chave de identificação para as espécies do gênero e uma discussão biogeográfica são apresentadas.

Nemadoras cristinae, new species of thorny catfish (Siluriformes: Doradidae) with redescriptions of its congeners

ABSTRACT. Nemadoras cristinae is described from the upper Amazonas/Solimões and Madeira basins in Brazil, Colombia and Peru, with additional specimens from the upper Meta (Orinoco basin), Colombia, tentatively treated as conspecific. Nemadoras cristinae is distinguished from congeners by having 3–9 premaxillary teeth in approximately two rows in juveniles and adults, outermost teeth weakly spatulate and innermost more acicular (vs. premaxillary edentulous in adults of all congeners and limited to 1–6 acicular teeth in juveniles of N. elongatus, N. humeralis, N. leporhinus and N. ternetzi); and mental barbels with extremely elongate (filiform) papillae, length of longest papillae about 4–7 times its width at base (vs. papillae shorter, length of longest <3 times its width at base). Nemadoras cristinae most closely resembles N. leporhinus, but is further distinguished from that species by having shaft and primary fimbriae of maxillary barbel smooth (vs. outer margin of shaft and margins of primary fimbriae with distinct secondary fimbriae). Nuptial specimens of N. cristinae exhibit sexual dimorphism; in males the pungent dorsal spine is greatly prolonged by a soft, flexible tip approximately 19.8–23.9% of the total dorsal spine length (vs. 5.3–9.4% in females). The sturdy, spatulate teeth in the upper and lower jaws of N. cristinae are evidently effective tools for raking caddisfly larvae from their attached substrates, as gut contents were dominated by cases and larval remnants of Nectopsyche (Leptoceridae). The six other species of Nemadoras are redescribed, the monophyly of the genus is discussed, and an identification key is provided. Detailed observations on the mesethmoid and infraorbital bones and associated sensory canal are reported for Nemadoras and compared to other species of fimbriate-barbel doradids.

Redescription and geographical distribution of the endangered fish Ossubtus xinguense Jegu 1992 (Characiformes, Serrasalmidae) with comments on conservation of the rheophilic fauna of the Xingu River

The monotypic species Ossubtus xinguense was originally described based on scarce material putatively divided into juveniles and adults. Ossubtus xinguense has a restricted distribution and was previously known only from a few rapids downstream of the city of Altamira, in the Volta Grande stretch of the Middle Xingu River. Until recently, the species was rare in museums because its habitat (large rapids) is difficult to sample. Large-scale collecting efforts targeting rapids throughout the Xingu River basin have yielded an abundance of new material. Based on an analysis of the type series and freshly preserved specimens, we redescribe O. xinguense and provide detailed osteological descriptions along with comments about its relationships within Serrasalmidae. Furthermore, we expand the geographical distribution of the species and discuss its conservation status.

A new species of Rhinopetitia Géry 1964 (Ostariophysi: Characiformes: Characidae) from the Rio Teles Pires, Rio Tapajós basin, Brazil

A new species of Rhinopetitia is described from the Rio Teles Pires, a major tributary of the Rio Tapajós. The new taxon is distinguished from its only congener, Rhinopetitia myersi, by having all premaxillary teeth in both rows with seven to nine cusps, maxillary teeth with seven or eight cusps, a distinct dark midlateral stripe on the body and a round humeral blotch (v. outer series of premaxillary teeth with three cusps and inner series of premaxillary teeth with three to five cusps, maxillary teeth with three to five cusps, the absence of a dark midlateral stripe and humeral blotch). Putative characters suggesting a close relationship between Rhinopetitia, Bryconacidnus, Ceratobranchia, Monotocheirodon, Odontostoechus, Othonocheirodus and Rhinobrycon are presented. This putative clade is included in the Stevardiinae, a monophyletic group within the Characidae.