John G Lundberg

Abstract Identifying the main taxonomic, phylogenetic and trait dimensions of beta diversity, and evaluating their prospective drivers, advances our understanding of patterns and processes involved in the evolution of biological assemblages. Using comprehensive databases on the distribution, phylogeny, and morphological traits of Amazonian freshwater fishes, we analyzed turnover beta diversity patterns of these three dimensions to evaluate prospective historical and contemporary drivers using multiple regression on distance matrices.We found mean taxonomic beta diversity about two times higher than mean phylogenetic and six times higher than species traits beta diversity, and coincident spatial patterns in Taxoβsim and Phyloβsim dimensions, whereas Traitβsim seemed more diffuse and heterogeneous across space. We find prominent influence of sub-basins geographic distances, habitat harshness and water color types on the taxonomic and phylogenetic dimensions of beta diversity, together with smaller individual effects of current temperature and habitat types, historical sub-basins connections and marine incursions, and sampling effort. By contrast, Traitβsim was weakly explained only by sampling effort and current sub-basins hydro-morphological conditions.These results point to leading effects of dispersal limitation, environmental filtering and historical contingencies in explaining Amazonian fish assemblages taxonomic and phylogenetic beta diversity patterns, but not functional traits turnover. Resumo Identificar as principais dimensões taxonômica, filogenética e de atributos da diversidade beta, e avaliar seus possíveis fatores determinantes, aprimora nossa compreensão dos padrões e processos envolvidos na evolução das assembleias biológicas. Utilizando bancos de dados abrangentes sobre a distribuição, filogenia e atributos morfológicos dos peixes de água doce amazônicos, analisamos os padrões de substituição de espécies dessas três dimensões para avaliar seus potenciais determinantes históricos e contemporâneos usando regressão múltipla em matrizes de distâncias. Observamos que a diversidade beta taxonômica média foi cerca de duas vezes maior que a diversidade beta filogenética média e seis vezes maior que a diversidade beta baseada em atributos das espécies, com padrões espaciais coincidentes nas dimensões Taxoβsim e Phyloβsim, enquanto a Traitβsim apresentou-se mais difusa e heterogênea no espaço. Nós encontramos a influência proeminente das distâncias geográficas entre sub-bacias, da severidade do habitat e dos tipos de cor da água nas dimensões taxonômica e filogenética da diversidade beta, junto com efeitos individuais menores da temperatura atual, tipos de habitat, conexões históricas entre sub-bacias, incursões marinhas e esforço amostral. Em contraste, a Traitβsim foi pouco explicada, sendo influenciada apenas pelo esforço amostral e pelas condições hidromorfológicas atuais das sub-bacias. Esses resultados apontam para efeitos predominantes da limitação de dispersão, filtragem ambiental e contingências históricas na explicação dos padrões de diversidade beta taxonômica e filogenética dos agrupamentos de peixes amazônicos, mas não na substituição de atributos funcionais.

ABSTRACT
The present study evaluated the phylogenetic relationships among the six valid species of catfish of the genus Hypophthalmus, estimated the divergence times among the different taxa and assessed the processes that influenced the evolution of the group. All the phylogenetic analyses, based on 6803 base pairs, including three mitochondrial and seven nuclear markers, support the monophyly of Hypophthalmus, and the arrangement of the species in two clades, one containing Hypophthalmus oremaculatus + Hypophthalmus donascimientoi, and the other, including Hypophthalmus marginatus + Hypophthalmus edentatus, which is the sister group of Hypophthalmus celiae, with Hypophthalmus fimbriatus appearing as the most divergent of this clade. These findings indicate that the genus originated some 4.4 million years ago (Ma), during the Pliocene, while most species diversified during the Pleistocene. The origin and diversification of Hypophthalmus coincided with the formation of the modern Amazon basin and the climatic fluctuations of the Plio‐Pleistocene, which likely determined modifications in the dynamics of the local rivers and influenced the evolution and diversification of the genus.

AbsractWe use synchrotron microtomography to study the osteology of an eyeless stygobitic catfish from South China with the objective of examining its systematic position. The results support to assign this species to the superfamily Sisoroidea. Proliobagrus He, Lundberg, Yang et Yang, gen. nov. is proposed diagnosed with a combination of characters: infraorbital bones reduced to one posteriormost element and lacrimal; mesocoracoid arch incomplete; first dorsal-fin pterygiophore compressed lacking paired bony canals for erector muscles, fused with an anteriorly directed process at its proximal end, and remote from Weberian complex; compound Weberian centrum with a ventral median ridge instead of paired ventrolateral ridges, an auxillary parapophysis posterolaterally off compound Weberian centrum, heavy strut-like process ventrally off the fourth neural spine, claustrum absent, tripus with outwardly extended transformator process; anterior cranial fontanelle closed, posterior cranial fontanelle subdivided into anterior and posterior remnant; first proximal pectoral-fin radial roughly round; dorsal and ventral procurrent caudal-fin rays less than ten respectively; base of nasal barbel on anterior rim of posterior nostril; skin lacking tubercles. In a first cladistic analysis, Proliobagrus is grouped with sampled amblycipitid species. The abrupt change of insert position of the first dorsal-fin pterygoid implies that none of extant amblycipitid species could be considered as direct ancestor of Proliobagrus and it represents a relic lineage surviving in subterranean waters.

Unlike most rivers globally, nearly all lowland Amazonian rivers have unregulated flow, supporting seasonally flooded floodplain forests. Floodplain forests harbor a unique tree species assemblage adapted to flooding and specialized fauna, including fruit-eating fish that migrate seasonally into floodplains, favoring expansive floodplain areas. Frugivorous fish are forest-dependent fauna critical to forest regeneration via seed dispersal and support commercial and artisanal fisheries. We implemented linear mixed effects models to investigate drivers of species richness among specialized frugivorous fishes across the ~6,000,000 km2 Amazon Basin, analyzing 29 species from 9 families (10,058 occurrences). Floodplain predictors per subbasin included floodplain forest extent, tree species richness (309,540 occurrences for 2,506 species), water biogeochemistry, flood duration, and elevation, with river order controlling for longitudinal positioning along the river network. We observed heterogeneous patterns of frugivorous fish species richness, which were positively correlated with floodplain forest extent, tree species richness, and flood duration. The natural hydrological regime facilitates fish access to flooded forests and controls fruit production. Thus, the ability of Amazonian floodplain ecosystems to support frugivorous fish assemblages hinges on extensive and diverse seasonally flooded forests. Given the low functional redundancy in fish seed dispersal networks, diverse frugivorous fish assemblages disperse and maintain diverse forests; vice versa, diverse forests maintain more fish species, underscoring the critically important taxonomic interdependencies that embody Amazonian ecosystems. Effective management strategies must acknowledge that access to diverse and hydrologically functional floodplain forests is essential to ensure the long-term survival of frugivorous fish and, in turn, the long-term sustainability of floodplain forests.

Abstract The São Francisco River basin in eastern Brazil harbors a highly endemic ichthyofauna, including the poorly known pimelodid catfishes Duopalatinus emarginatus and Bagropsis reinhardti. Despite being described in the 19th century, these species have remained taxonomically obscure due to limited specimen availability and confusion with other taxa. In this study, we provide detailed redescriptions of both species based on recently collected and newly identified material, including misidentified museum specimens. Morphological comparisons and osteological data confirm that Duopalatinus emarginatus and Bagropsis reinhardti are distinct, differing in several skeletal and meristic characters, as well as habitat preferences. Our findings support a revised classification within Pimelodidae, with Bagropsis (now including Pimelodus atrobrunneus and P. paranaensis) and Duopalatinusemarginatus together forming the newly proposed tribe Bagropsini. We also present updated distributional data, highlighting the distinct ecological niches occupied by each species within the São Francisco basin. These redescriptions are crucial for accurate species identification and have direct implications for conservation assessments. Key identification to Pimelodidae species from São Francisco River basin is provided.
Resumo A bacia do rio São Francisco, no leste do Brasil, abriga uma ictiofauna altamente endêmica, incluindo os bagres pimelodídeos pouco conhecidos Duopalatinus emarginatus e Bagropsis reinhardti. Apesar de descritas no século XIX, essas espécies permaneceram obscuras do ponto de vista taxonômico devido à disponibilidade limitada de espécimes e à confusão com outros táxons. Neste estudo, fornecemos redescrições detalhadas de ambas as espécies com base em material recentemente coletado e recém-identificado, incluindo espécimes de museu anteriormente identificados de forma incorreta. Comparações morfológicas e dados osteológicos confirmam que Duopalatinus emarginatus e Bagropsis reinhardti são espécies distintas, diferindo em vários caracteres esqueléticos e merísticos, bem como em preferências de habitat. Nossos resultados sustentam uma classificação revisada dentro de Pimelodidae, com Bagropsis (agora incluindo Pimelodus atrobrunneus e P. paranaensis) e Duopalatinus emarginatus juntos formando a tribo recém-proposta Bagropsini. Também apresentamos dados de distribuição atualizados, destacando os nichos ecológicos distintos ocupados por cada espécie dentro da bacia do São Francisco. Essas redescrições são essenciais para a identificação precisa das espécies e têm implicações diretas para avaliações de conservação. É fornecida uma chave de identificação das espécies de Pimelodidae da bacia do rio São Francisco.

The pimelodid genus Hypophthalmus is a small group of pelagic and planktivorous catfishes that are abundant and variously distributed in the lowland river basins of the Amazon, Parnaíba, Orinoco, Guianas and Paraná. Since their earliest published descriptions, commencing over 190 years ago with H. edentatus Spix and Agassiz 1829, the taxonomy and nomenclature of Hypophthalmus species have been confused and unresolved. In this study, four of the six available species names are validated and two new species are described. Newly discovered characters of the vertebral column, circumoral barbels, pelvic fins, and lateralis sensory canals provide strong support and diagnostics for species and species-groups. A key to species, anatomical descriptions, notes on identification of small juveniles and phylogenetic interrelationships are included. A lectotype is designated for Hypophthalmus marginatus and nominal Hypophthalmus longifilis, respectively.

The Amazon Basin is an unquestionable biodiversity hotspot, containing the highest freshwater biodiversity on earth and facing off a recent increase in anthropogenic threats. The current knowledge on the spatial distribution of the freshwater fish species is greatly deficient in this basin, preventing a comprehensive understanding of this hyper-diverse ecosystem as a whole. Filling this gap was the priority of a transnational collaborative project, i.e. the AmazonFish project - . Relying on the outputs of this project, we provide the most complete fish species distribution records covering the whole Amazon drainage. The database, including 2,406 validated freshwater native fish species, 232,936 georeferenced records, results from an extensive survey of species distribution including 590 different sources (e.g. published articles, grey literature, online biodiversity databases and scientific collections from museums and universities worldwide) and field expeditions conducted during the project. This database, delivered at both georeferenced localities (21,500 localities) and sub-drainages grains (144 units), represents a highly valuable source of information for further studies on freshwater fish biodiversity, biogeography and conservation.

A recent boom in hydroelectric development in the world's most diverse tropical river basins is currently threatening aquatic biodiversity on an unprecedented scale. Among the most controversial of these projects is the Belo Monte Hydroelectric Complex (BMHC) on the Xingu River, the Amazon's largest clear-water tributary. The design of the BMHC creates three distinctly altered segments: a flooded section upstream of the main dam, a middle section between the dam and the main powerhouse that will be dewatered, and a downstream section subject to flow alteration from powerhouse discharge. This region of the Xingu is notable for an extensive series of rapids known as the Volta Grande that hosts exceptional levels of endemic aquatic biodiversity; yet, patterns of temporal and spatial variation in community composition within this highly threatened habitat are not well documented. We surveyed fish assemblages within rapids in the three segments impacted by the BMHC prior to hydrologic alteration, and tested for differences in assemblage structure between segments and seasons. Fish species richness varied only slightly between segments, but there were significant differences in assemblage structure between segments and seasons. Most of the species thought to be highly dependent on rapids habitat, including several species listed as threatened in Brazil, were either restricted to or much more abundant within the upstream and middle segments. Our analysis identified the middle section of the Volta Grande as critically important for the conservation of this diverse, endemic fish fauna. Additional research is urgently needed to determine dam operations that may optimize energy production with an environmental flow regime that conserves the river's unique habitat and biodiversity. •193 rapids-dwelling fish species were sampled prior to flow alteration.•Fish community structure differed significantly between river segments.•Rapids specialists and threatened species were concentrated in the Volta Grande.•The Volta Grande rapids are now flooded and dewatered due to a hydropower facility.•Maintaining rapids in the dewatered section will be critical for aquatic diversity.

We performed the first combined-data phylogenetic analysis of ictalurids including most living and fossil species. We sampled 56 extant species and 16 fossil species representing outgroups, the seven living genera, and the extinct genus dagger Astephus long thought to be an ictalurid. In total, 209 morphological characters were curated and illustrated in MorphoBank from published and original work, and standardized using reductive coding. Molecular sequences harvested from GenBank for one nuclear and four mitochondrial genes were combined with the morphological data for total evidence analysis. Parsimony analysis recovers a crown clade Ictaluridae composed of seven living genera and numerous extinct species. The oldest ictalurid fossils are the Late Eocene members of Ameiurus and Ictalurus. The fossil clade dagger Astephus placed outside of Ictaluridae and not as its sister taxon. Previous morphological phylogenetic studies of Ictaluridae hypothesized convergent evolution of troglobitic features among the subterranean species. In contrast, we found morphological evidence to support a single clade of the four troglobitic species, the sister taxon of all ictalurids. This result holds whether fossils are included or not. Some previously published clock-based age estimates closely approximate our minimum ages of clades. (C) The Willi Hennig Society 2016.