Intertidal life: Field observations on the clingfish gobiesox barbatulus in southeastern Brazil

The clingfish Gobiesox barbatulus shows nocturnal feeding activity, spending most part of the day stationary and adhered to the inferior part of stones. To feed, this species uses the sit-and-wait and particulate feeding tactics. It shows a carnivorous feeding habit mostly consuming small benthic crustaceans. It can move in two ways: (1) "stone-by-stone", sliding its ventral sucker disc across each stone and (2) "surf", when it takes advantage of the energy of the ebbing tide to quickly cross a distance up to four times its body length. Its reproductive season occurs between the end of spring and the beginning of summer, during which time it lays about 2,000 adhesive eggs of 1 mm each in a single layer under stones. It has more than one egg-laying session per reproductive season, therefore showing several different developmental stages. It performs fanning, mouthing and guarding of the eggs as forms of parental care. Data shown here also indicates that G. barbatulus has some shelter fidelity, being probably territorial. © 2011 Sociedade Brasileira de Ictiologia

Trends in studies of Brazilian stream fish assemblages

Studies about fish assemblages in Brazilian streams have grown in recent years, however, it remains unclear whether this increase is followed by increments in the diversity of addressed topics and theoretical frameworks adopted by researchers. We performed a systematic search for Brazilian studies on stream fish assemblages recording study region, publication year, objectives, and spatial and temporal scales adopted. The number of studies is unevenly distributed among regions. Most papers describe the general structure of local fish assemblages and their scientific objectives have not varied through time. Studies have been conducted mainly at small temporal and spatial scales, though the latter is increasing over time. We argue for the need of focusing on recently developed ecological theories and frameworks, and expanding the temporal and spatial scales of studies. These changes will improve regional and local conservation policies, and the visibility of aquatic Brazilian research in the global scientific community. © 2016 Associação Brasileira de Ciência Ecológica e Conservaçã

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

Revisiting Amazonian water types: experimental evidence highlights the importance of forest stream hydrochemistry in shaping adaptation in a fish species

Following Alfred Russel Wallace, Amazonian freshwaters are classified into three types: black, white, and clear. Such waters have been demonstrated to affect adaptation and gene flow of the aquatic fauna. However, this classification focuses on large rivers and fails to acknowledge the importance of small forest streams that flow through upland terra firme forests, known as igarapés. Igarapés are surrounded by a distinct floristic composition when compared to the floodplains and contribute with a much greater water load to the Amazon basin than the Amazon River itself. We assessed the importance of blackwater, whitewater, and igarapé water on spawning and habitat choice in Crenuchus spilurus, a small fish composed of distinct genetic lineages that occur in igarapés flowing to blackwater and whitewater systems. Lineages from igarapés connected to the Rio Negro (blackwater) and Amazon River (whitewater) basins have greater spawning success in igarapé water than in the water from their surrounding floodplain. Habitat choice trials showed active selection of igarapé water by both lineages. Our results indicate that the hydrochemical condition of igarapés shapes adaptation in the physiology and behavior of C. spilurus. We suggest expanding upon the current classification to include igarapés as a distinct water type and environment. © 2019, Springer Nature Switzerland AG

Traits of a lineage with extraordinary geographical range: ecology, behavior and life-history of the sailfin tetra Crenuchus spilurus

Current broad geographical distributions of species can only exist because individuals dispersed from their natal sites. The Amazon’s sailfin tetra Crenuchus spilurus has a geographical range of over 3 million km2, an area 5.7 times larger than France, which includes regions of very distinct abiotic and biotic conditions. What traits may aid in explaining such a broad geographical range, and which make the range exceptional? Here we investigate the species’ ecology and behavior using several approaches: direct field observations, ecological surveys, analyses of reproductive parameters, and diet. Broad trophic niche and frequent reproduction may help explain the wide geographical range, whereas most other traits are typical of short-ranged species: small body size, specific habitat requirements, small populations, low mobility, site-fidelity, low fecundity, and large relative size at maturation. We propose that the broad geographical range of C. spilurus is better explained by passive processes related to river dynamics. Interestingly, this species is one of few strongly dichromatic species of Amazon fish, having mutual signaling during courtship, and males exerting exclusive parental care of eggs and early larval stages. While the combination of such behavioral and ecological characteristics should promote differences among lineages and (eventually) speciation, populations far apart are remarkably morphologically similar. We suggest that ecology along with sexual selection may interplay and contribute to the inter-population morphological similarity, criterion on which Crenuchus is considered a monotypic genus. © 2016, Springer Science+Business Media Dordrecht

Sensory drive in colourful waters: Morphological variation suggests combined natural and sexual selection in an Amazonian fish

Natural selection often shapes visual perception with respect to the lighting environment. For organisms that rely on visual communication for mating, environmental backscatter and bias in wavelength transmission affect the exchange of visual signals, which can mediate major changes in sexually selected traits. Based on the lighting environment, Amazon forest streams (igarapés) can be categorized into two major water types: clearwater and blackwater. The lighting environment is mostly transparent in clearwater, whereas retention of high amounts of dissolved organic carbon biases light towards the red and creates strong backscatter in blackwater igarapés. We investigated morphological differences among populations representative of lineages within the sailfin tetra Crenuchus spilurus, a sexually dichromatic Amazonian fish. We show that despite the broad geographical range of the nominal species, populations are similar for most measured morphological traits. However, eye diameter and characteristics of the fin ornaments revealed two distinct groups, corresponding to lineages from blackwater and clearwater igarapés. Our results lend support to the sensory drive hypothesis by suggesting that as a consequence of animals inhabiting different lighting conditions, natural selection affected visual perception and thus resulted in differences in sexual ornaments. © 2019 The Linnean Society of London, Biological Journal of the Linnean Society

Ecology and life-history of Mesonauta festivus: biological traits of a broad ranged and abundant Neotropical cichlid

The cichlid Mesonauta festivus is common and abundant among macrophyte stands along a large geographical range of the Amazonas and Paraná-Paraguay basins, in South America. This broad geographical range highlights the species’ dispersion ability, which can be attributed to specific biological and behavioral traits. However, the dispersion ability does not account for the broad geographical range alone, as the species must be able to establish populations in a range of environments, which include marginal areas of large rivers with different water types, floodplain lakes, and small terra-firme streams. In this work we investigated the specie’s ecology, biological traits and behavior in order to understand what and how its traits may have allowed it to attain such broad geographical range and aid in establishing local populations. Regarding its dispersion ability we stress the capability of swimming in the pelagic region, which is remarkable for this species and uncommon among Neotropical cichlids. Its vagility is high even when juveniles are under parental care. Regarding population establishment, the high environmental tolerance stands out, allowing the species to live under strikingly different abiotic conditions. In addition, the small size of first sexual maturation and its capability of spawning along the whole hydrologic cycle (apparently not associated to a specific environmental cue) may also facilitate the establishment of populations into new environments. Moreover, the behavior of mimicking dead leaves, which is mainly performed by juveniles, may lessen predation pressures. Under an eco-evolutionary perspective, the traits highlighted in this work may buffer selective pressures experienced by populations in different biotic and/or abiotic conditions, which may also favor the increasing of the geographical range by allowing the evolutionary lineage to remain similar even in disconnected and/or striking different environments. © 2014, Springer Science+Business Media Dordrecht

The use of taxonomic families as biological surrogates of the diversity of the Amazonian stream fish

The reliable identification of the fish species found in Amazonian streams requires a considerable investment of both time and resources, which often hampers the biodiversity pattern mapping and conservation planning. This problem can be overcome using biological surrogates such taxonomic families, this would reduce the number of fish to be identified and thus facilitate the development of studies. The present study analyzes the potential of families as surrogates of the fish diversity of Amazonian streams. For this, we verified the degree of congruence between the distribution of species organized by family and the composition of the assemblage in two different spatial scenarios. At the biome scale, we verified the degree of congruence in the fish faunas of 54 streams located within six drainage basins in Brazilian Amazonia. At the regional scale, we compared the data from the basins located on the lowland floodplain and those at higher altitudes. The Cichlidae and Lebiasinidae were identified as potential biological surrogates at both spatial scenarios, demonstrating more than 80% similarity with species matrix in all the analytical approaches. The families Crenuchidae and Hypopomidae were the most congruent with the fish from the floodplain basins, both were more than 80% congruent with the species matrix. In upland basins, Characidae, Gymnotidae and Rivulidae were highly similar to the species matrix, in particular Gymnotidae and Rivulidae with more than 90% similarity. Overall, we can conclude that the biological surrogacy approach is a potentially valuable alternative for species diversity evaluation of Amazonian streams ecosystems, considering the accelerated loss of the diversity of these systems

Testing Wallace's intuition: water type, reproductive isolation and divergence in an Amazonian fish

Alfred Russel Wallace proposed classifying Amazon rivers based on their colour and clarity: white, black and clear water. Wallace also proposed that black waters could mediate diversification and yield distinct fish species. Here, we bring evidence of speciation mediated by water type in the sailfin tetra (Crenuchus spilurus), a fish whose range encompasses rivers of very distinct hydrochemical conditions. Distribution of the two main lineages concords with Wallace's water types: one restricted to the acidic and nutrient-poor waters of the Negro River (herein Rio Negro lineage) and a second widespread throughout the remaining of the species’ distribution (herein Amazonas lineage). These lineages occur over a very broad geographical range, suggesting that despite occurring in regions separated by thousands of kilometres, individuals of the distinct lineages fail to occupy each other's habitats, hundreds of metres apart and not separated by physical barrier. Reproductive isolation was assessed in isolated pairs exposed to black-water conditions. All pairs with at least one individual of the lineage not native to black waters showed significantly lower spawning success, suggesting that the water type affected the fitness and contributed to reproductive isolation. Our results endorse Wallace's intuition and highlight the importance of ecological factors in shaping diversity of the Amazon fish fauna. © 2018 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2018 European Society For Evolutionary Biolog