Unstable environmental conditions constrain the fine-tune between opsin sensitivity and underwater light in an Amazon forest stream fish.

Visual adaptations can stem from variations in amino acid composition, chromophore utilization, and differential opsin gene expression levels, enabling individuals to adjust their light sensitivity to environmental lighting conditions. In stable environments, adaptations often involve amino acid substitutions, whereas in unstable conditions, differential gene expression may be a more relevant mechanism. Amazon forest streams present diverse underwater lighting conditions and experience short-term water colour fluctuations. In these environments, it is less likely for genetic and amino acid sequences to undergo modifications that tailor opsin proteins to the prevailing lighting conditions, particularly in species having several copies of the same gene. The sailfin tetra, Crenuchus spilurus, inhabits black and clear water Amazon forest streams. The long-wavelength sensitivity (LWS) is an important component for foraging and courtship. Here, we investigated LWS opsin genes in the sailfin tetra. Three copies of LWS1 and two copies of LWS2 genes were found. The maximum absorbance wavelength (λmax) estimated from the amino acid sequences of LWS1 genes exhibited variation among the different copies. In contrast, the copies of LWS2 genes showed identical expected λmax values. Although the amino acid positions affecting λmax varied among LWS genes, they remained consistent among populations living in different water colours. The relative expression levels of LWS genes differed between gene copies. While not formally tested, our results suggest that in fluctuating environments, visual adaptations may primarily stem from alterations in gene expression profiles and/or chromophore usage rather than precise genetic tuning of protein light sensitivity to environmental lighting conditions.

Long-term Ecological Research: Chasing fashions or being prepared for fashion changes?

Long-term-ecological-research (LTER) faces many challenges, including the difficulty of obtaining long-term funding, changes in research questions and sampling designs, keeping researchers collecting standardized data for many years, impediments to interactions with local people, and the difficulty of integrating the needs of local decision makers with "big science". These issues result in a lack of universally accepted guidelines as to how research should be done and integrated among LTER sites. Here we discuss how the RAPELD (standardized field infrastructure system), can help deal with these issues as a complementary technique in LTER studies, allowing comparisons across landscapes and ecosystems and reducing sampling costs. RAPELD uses local surveys to understand broad spatial and temporal patterns while enhancing decision-making and training of researchers, local indigenous groups and traditional communities. Sampling of ecological data can be carried out by different researchers through standardized protocols, resulting in spatial data that can be used to answer temporal questions, and allow new questions to be investigated. Results can also be integrated into existing biodiversity networks. Integrated systems are the most efficient way to save resources, maximize results, and accumulate information that can be used in the face of the unknown unknowns upon which our future depends.

Effect of light bias on male mating signal and female mate choice in a sexually dimorphic Amazon fish.

Colourful signals are usually honest indicators of mate quality since they are energetically costly. However, how colours are perceived by choosers is highly affected by the environmental light condition. Amazon black waters are strongly red-biased while clear waters show no apparent colour bias. The sailfin tetra Crenuchus spilurus is a sexually dimorphic Amazon fish species; males have hyperallometric dorsal and anal fins conspicuously ornamented with red and yellow markings. The species has two main lineages, which inhabit black and clear waters. A comparison of the red colouration of the ornaments of males from different lineages indicates that red bias increases the perceived intensity of red colouration but decreases the perceived among-individual variation in red colour. In mate choice experiments, females from all lineages preferred males with larger ornaments. Clear water lineage females were more likely to accept males under red-biased lighting, which increases the apparent red colouration, suggesting the importance of the red colouration in their mate choice. On the other hand, male acceptance by females from black waters did not change under different light conditions, suggesting that signals other than the red colouration (e.g. size of ornaments) were more important in their mate choice.

Pervasive gaps in Amazonian ecological research.

Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5,6,7 vast areas of the tropics remain understudied.8,9,10,11 In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepresented in biodiversity databases.13,14,15 To worsen this situation, human-induced modifications16,17 may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%-18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost.

The critical role of natural history museums in advancing eDNA for biodiversity studies: a case study with Amazonian fishes.

Ichthyological surveys have traditionally been conducted using whole-specimen, capture-based sampling with varied but conventional fishing gear. Recently, environmental DNA (eDNA) metabarcoding has emerged as a complementary, and possible alternative, approach to whole-specimen methodologies. In the tropics, where much of the diversity remains undescribed, vast reaches continue unexplored, and anthropogenic activities are constant threats; there have been few eDNA attempts for ichthyological inventories. We tested the discriminatory power of eDNA using MiFish primers with existing public reference libraries and compared this with capture-based methods in two distinct ecosystems in the megadiverse Amazon basin. In our study, eDNA provided an accurate snapshot of the fishes at higher taxonomic levels and corroborated its effectiveness to detect specialized fish assemblages. Some flaws in fish metabarcoding studies are routine issues addressed in natural history museums. Thus, by expanding their archives and adopting a series of initiatives linking collection-based research, training and outreach, natural history museums can enable the effective use of eDNA to survey Earth's hotspots of biodiversity before taxa go extinct. Our project surveying poorly explored rivers and using DNA vouchered archives to build metabarcoding libraries for Neotropical fishes can serve as a model of this protocol.

Putative poison gland in the thorny catfish Acanthodoras spinosissimus (Siluriformes: Doradidae) / Suposta glândula de veneno no bagre rebeca Acanthodoras spinosissimus (Siluriformes: Doradidae)

Acanthodoras is the only genus of catfish known to secrete a conspicuous and abundant milky-looking substance through an axillary pore located just below the base of the posterior cleithral process. Despite this remarkable feature, there is no published information on the anatomical structures that produce the secretion and its possible biological/ecological functions. Dissection and histological analysis of preserved specimens of A. spinosissimus revealed the presence of a saccular axillary gland with large, binuclear secretory cells, similar to those found in other poisonous catfish. Secretory cells near the lumen appear to lose nuclei and become filled with secretory products, possibly with proteinaceous elements, as indicated by their eosinophilic appearance. As far as we know, the saccular morphology of the gland appears to constitute a unique characteristic of Acanthodoras among Doradidae catfishes. Further studies are necessary to determine the chemical composition of the secretion, as well as its possible uses by the catfish in its natural environment.

Acanthodoras é o único gênero de bagre conhecido por secretar uma substância de aparência leitosa conspícua e abundante através de um poro axilar localizado logo abaixo da base do processo cleitral posterior. Apesar dessa característica marcante, não há informações publicadas sobre as estruturas anatômicas que produzem a secreção, nem sobre suas possíveis funções biológicas/ecológicas. A dissecção e análise histológica de espécimes preservados de A. spinosissimus revelaram a presença de uma glândula axilar sacular com células secretoras binucleares, semelhantes às encontradas em outros bagres venenosos. As células secretoras próximas ao lúmen parecem perder os núcleos e são preenchidas com produtos secretores, possivelmente com elementos proteicos, conforme indicado por sua aparência eosinofílica. Até onde sabemos, a morfologia sacular da glândula parece constituir uma característica única de Acanthodoras entre os bagres Doradidae. Mais estudos são necessários para determinar a composição química da secreção, bem como seus possíveis usos pelo bagre em seu ambiente natural.

Putative poison gland in the thorny catfish Acanthodoras spinosissimus (Siluriformes: Doradidae)

ABSTRACT Acanthodoras is the only genus of catfish known to secrete a conspicuous and abundant milky-looking substance through an axillary pore located just below the base of the posterior cleithral process. Despite this remarkable feature, there is no published information on the anatomical structures that produce the secretion and its possible biological/ecological functions. Dissection and histological analysis of preserved specimens of A. spinosissimus revealed the presence of a saccular axillary gland with large, binuclear secretory cells, similar to those found in other poisonous catfish. Secretory cells near the lumen appear to lose nuclei and become filled with secretory products, possibly with proteinaceous elements, as indicated by their eosinophilic appearance. As far as we know, the saccular morphology of the gland appears to constitute a unique characteristic of Acanthodoras among Doradidae catfishes. Further studies are necessary to determine the chemical composition of the secretion, as well as its possible uses by the catfish in its natural environment.

RESUMO Acanthodoras é o único gênero de bagre conhecido por secretar uma substância de aparência leitosa conspícua e abundante através de um poro axilar localizado logo abaixo da base do processo cleitral posterior. Apesar dessa característica marcante, não há informações publicadas sobre as estruturas anatômicas que produzem a secreção, nem sobre suas possíveis funções biológicas/ecológicas. A dissecção e análise histológica de espécimes preservados de A. spinosissimus revelaram a presença de uma glândula axilar sacular com células secretoras binucleares, semelhantes às encontradas em outros bagres venenosos. As células secretoras próximas ao lúmen parecem perder os núcleos e são preenchidas com produtos secretores, possivelmente com elementos proteicos, conforme indicado por sua aparência eosinofílica. Até onde sabemos, a morfologia sacular da glândula parece constituir uma característica única de Acanthodoras entre os bagres Doradidae. Mais estudos são necessários para determinar a composição química da secreção, bem como seus possíveis usos pelo bagre em seu ambiente natural.

Cytogenetic Analysis of Panaqolus tankei Cramer & Sousa, 2016 (Siluriformes, Loricariidae), an Ornamental Fish Endemic to Xingu River, Brazil.

Despite conservation of the diploid number, a huge diversity in karyotype formulae is found in the Ancistrini tribe (Loricariidae, Hypostominae). However, the lack of cytogenetic data for many groups impairs a comprehensive understanding of the chromosomal relationships and the impact of chromosomal changes on their evolutionary history. Here, we present for the first time the karyotype of Panaqolus tankei Cramer & Sousa, 2016. We focused on the chromosomal characterization, using conventional and molecular cytogenetic techniques to unravel the evolutionary trends of this tribe. P. tankei, as most species of its sister group Pterygoplichthini, also possessess a conserved diploid number of 52 chromosomes. We observed heterochromatin regions in the centromeres of many chromosomes; pairs 5 and 6 presented interstitial heterochromatin regions, whereas pairs 23 and 24 showed extensive heterochromatin regions in their q arms. In situ localization of 18S rDNA showed hybridization signals correlating with the nucleolus organizer regions, which are located in the q arms of pair 5. However, the 5S rDNA was detected in the centromeric and terminal regions of the q arms of pair 8. (TTAGGG)n hybridized only in the terminal regions of all chromosomes. Microsatellite in situ localization showed divergent patterns, (GA)15 repeated sequences were restricted to the terminal regions of some chromosomes, whereas (AC)15 and (GT)15 showed a scattered hybridization pattern throughout the genome. Intraspecific comparative genomic hybridization was performed on the chromosomes of P. tankei to verify the existence of sex-specific regions. The results revealed only a limited number of overlapping hybridization signals, coinciding with the heterochromatin in centromeric regions without any sex-specific signals in both males and females. Our study provides a karyotype description of P. tankei, highlighting extensive differences in the karyotype formula, the heterochromatin regions, and sites of 5S and 18S rDNA, as compared with data available for the genus.

Social predation in electric eels.

Social predation-when groups of predators coordinate actions to find and capture prey-is a common tactic among mammals but comparatively rare in fishes. We report the unexpected social predation by electric eels, an otherwise solitary predator in the Amazon rainforest. Observations made in different years and recorded on video show electric eels herding, encircling shoals of small nektonic fishes, and launching joint predatory high-voltage strikes on the prey ball. These findings challenge the hypothesis that electric eels may have a single foraging strategy and extend our knowledge on social predation to an organism that employs high-voltage discharge for hunting. Thereby offering a novel perspective for studies on the evolutionary interplay between predatory and escape tactics.

Taxonomic revision of Hopliancistrus Isbrücker & Nijssen, 1989 (Siluriformes, Loricariidae) with redescription of Hopliancistrus tricornis and description of four new species.

Hopliancistrus is an Ancistrini genus diagnosed by having few and very strong cheek odontodes on interopercular area, and a patch of strong and stiff odontodes on the antero-lateral border of the snout. The type species is herein redescribed based on types and recently collected specimens. In addition, four new congeneric species are described based on specimens collected in other parts of the Rio Xingu and Rio Tapajós basins. Hopliancistrus tricornis is distributed in the lower Rio Tapajós and is diagnosed by the possession of four branched anal-fin rays and relatively large white to yellow spots on trunk and pectoral and pelvic fins, and dark brown spots on dorsal, caudal and anal fins. Hopliancistrus munduruku is described based on specimens from Rio Jamanxim (Rio Tapajós basin) and Rio Curuá (Rio Xingu basin) and is diagnosed by the possession of five branched anal-fin rays and large yellow blotches on trunk and dark brown to black spots over the fins. Hopliancistrus wolverine is distributed in the rapids of the lower and middle Rio Xingu and is diagnosed by the possession of five branched anal-fin rays and conspicuous small yellow dots on head, trunk and fins. Hopliancistrus xikrin is distributed in medium- to small-sized tributaries of the lower portion of Rio Xingu basin, and is diagnosed by absence of contact between the transverse process of the first dorsal-fin pterygiophore and the transverse process of the second pterygiophore. Hopliancistrus xavante is distributed in the tributaries of upper Rio Xingu basin, and is diagnosed by having a thick skin covering the nuchal plate; by having large white spots on trunk and fins; and by the possession of five branched anal-fin rays. An osteological description and a key for species identification are also provided.

Organization of the cephalic lateral-line canals in Electrophorus varii de Santana, Wosiacki, Crampton, Sabaj, Dillman, Mendes-Júnior & Castro e Castro, 2019 (Gymnotiformes: Gymnotidae)

Electrophorus spp. generate high-voltage electric discharges for defense and hunting, and low-voltage electric discharges (as other Gymnotiformes) for electrolocation and communication. Despite intense interest in the unusual electrogenic and electroreceptive capacities of electric eels, the other sensory systems of Electrophorus spp. are relatively poorly known. Here we describe the ontogenetic development and organization of the cephalic lateral-line canals in the lowland electric eel, Electrophorus varii. Preserved specimens of larvae, juveniles, and adults were examined to describe the spatial distribution of the canals and pores. Ontogenetic shifts of the cephalic lateral line formation were observed for each canal and support a hypothesis of non-synchronized development. The morphogenesis of cephalic canals in larvae and juveniles begins just before the onset of exogenous feeding. In adults, the cephalic sensory canals are formed separately from the skull and overlay cranial and mandibular bones and muscles. This study provides the first detailed description of the development and organization of the cephalic lateral-line system in Electrophorus varii.(AU)

Electrophorus spp. geram descargas elétricas de alta voltagem, usadas para defesa e caça, e (como os demais Gymnotiformes) descargas elétricas de baixa voltagem para eletrolocalização e comunicação. Apesar do grande interesse nas capacidades eletrogênicas e eletrorreceptivas incomuns dos poraquês, os outros sistemas sensoriais de Electrophorus spp. são relativamente pouco conhecidos. Aqui nós descrevemos o desenvolvimento ontogenético e a organização dos canais da linha lateral cefálica no poraquê da planície Electrophorus varii. Exemplares preservados de larvas, juvenis e adultos foram analisados para descrever a distribuição espacial dos canais e poros. Variações ontogenéticas na formação da linha lateral cefálica foram observadas para cada canal, apresentando um desenvolvimento não-sincronizado. Variações ontogenéticas da formação da linha lateral cefálica foram observadas para cada canal e suportam uma hipótese de desenvolvimento assincrônico. A morfogênese dos canais cefálicos em larvas e juvenis precede o início da alimentação exógena. Nos adultos, os canais sensoriais cefálicos se formam separadamente do crânio e sobrepõem os ossos e músculos cranianos e mandibulares. Este estudo fornece a primeira descrição detalhada do desenvolvimento e organização do sistema da linha lateral cefálica de Electrophorus varii.(AU)

Integrated terrestrial-freshwater planning doubles conservation of tropical aquatic species.

Conservation initiatives overwhelmingly focus on terrestrial biodiversity, and little is known about the freshwater cobenefits of terrestrial conservation actions. We sampled more than 1500 terrestrial and freshwater species in the Amazon and simulated conservation for species from both realms. Prioritizations based on terrestrial species yielded on average just 22% of the freshwater benefits achieved through freshwater-focused conservation. However, by using integrated cross-realm planning, freshwater benefits could be increased by up to 600% for a 1% reduction in terrestrial benefits. Where freshwater biodiversity data are unavailable but aquatic connectivity is accounted for, freshwater benefits could still be doubled for negligible losses of terrestrial coverage. Conservation actions are urgently needed to improve the status of freshwater species globally. Our results suggest that such gains can be achieved without compromising terrestrial conservation goals.

A new Hyphessobrycon (Characiformes: Characidae) of the Hyphessobrycon heterorhabdus species-group from the Central Amazon basin, Brazil.

A new species of Hyphessobrycon Durbin from the Paraná do Urariá system in Central Amazon region, Amazonas state, Brazil, is described. The new species is allocated into the Hyphessobrycon heterorhabdus species-group due to its color pattern, composed by a well-defined, horizontally elongated humeral blotch continuous with a conspicuous midlateral dark stripe that becomes blurred towards the caudal peduncle, and can be distinguished from all other species of the group by possessing humeral blotch and continuous midlateral stripe broad, occupying vertical height equivalent of two scale rows. A tricolored pattern composed dorsally by a red or reddish longitudinal stripe, a middle iridescent, golden or silvery longitudinal stripe, and ventrally by a variably-developed longitudinal dark stripe is identified as a putative additional character shared by the species of the Hyphessobrycon heterorhabdus species-group. The presence of bony hooks in all fins in mature males of some species of the Hyphessobrycon heterorhabdus species-group is also discussed.

The combined effects of climate change and river fragmentation on the distribution of Andean Amazon fishes.

Upstream range shifts of freshwater fishes have been documented in recent years due to ongoing climate change. River fragmentation by dams, presenting physical barriers, can limit the climatically induced spatial redistribution of fishes. Andean freshwater ecosystems in the Neotropical region are expected to be highly affected by these future disturbances. However, proper evaluations are still missing. Combining species distribution models and functional traits of Andean Amazon fishes, coupled with dam locations and climatic projections (2070s), we (a) evaluated the potential impacts of future climate on species ranges, (b) investigated the combined impact of river fragmentation and climate change and (c) tested the relationships between these impacts and species functional traits. Results show that climate change will induce range contraction for most of the Andean Amazon fish species, particularly those inhabiting highlands. Dams are not predicted to greatly limit future range shifts for most species (i.e., the Barrier effect). However, some of these barriers should prevent upstream shifts for a considerable number of species, reducing future potential diversity in some basins. River fragmentation is predicted to act jointly with climate change in promoting a considerable decrease in the probability of species to persist in the long-term because of splitting species ranges in smaller fragments (i.e., the Isolation effect). Benthic and fast-flowing water adapted species with hydrodynamic bodies are significantly associated with severe range contractions from climate change.

A journey through the Amazon Middle Earth reveals Aspidoras azaghal (Siluriformes: Callichthyidae), a new species of armoured catfish from the rio Xingu basin, Brazil.

Aspidoras azaghal n. sp. was discovered during a multitaxonomic scientific expedition to the remote Amazon Terra do Meio region in tributaries to the rio Xingu basin, Pará, Brazil. The new species can be promptly distinguished from its congeners by the following combination of features: (a) absence of the first dorsal-fin element; (b) parieto-supraoccipital fontanel located medially on bone; (c) absence of a longitudinal dark-brown or black stripe along flank midline; (d) ventral surface of trunk covered by clearly smaller, irregular and/or roundish platelets; (e) inner laminar expansion of infraorbital 1 well developed; (f) relatively wide frontal bone, with width equal to half of entire length; (g) absence of a thick, longitudinal conspicuous dark-brown stripe along dorsal portion of flank; and (h) poorly developed serrations on posterior margin of the pectoral-fin spine. Besides morphological evidence, the molecular analyses indicated significant differences between the new species and its congeners, with A. albater and A. raimundi as its closest species, showing 6.53% of genetic differentiation in both cases. The intraspecific molecular data revealed gene flow (peer fixation index, FST = 0.05249, P > 0.05, for the cytochrome oxidase I (COI) marker and FST = -0.01466, P > 0.05, for the control region) between specimens upstream and downstream from a 30-m height waterfall at the type-locality, which therefore represent a single population. Furthermore, it was possible to observe a unidirectional gene flow pattern, with genetic diversity increasing in the downstream direction.

A database of freshwater fish species of the Amazon Basin.

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 - https://www.amazon-fish.com/. 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.