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Reproductive behaviour is often targeted by behavioural parasitism due to its high energy costs and direct relationship with fitness. Courtship behaviour represents a substantial amount of the investment in reproduction, as it usually requires conspicuous movements that are energetically demanding and increase predation risk. Here, we present an alternative reproductive tactic in which dominant male sailfin tetra, Crenuchus spilurus Gunther 1863, parasitize the courtship behaviour of subordinate males. By conducting field observations and controlled experiments in laboratory, we show that, under low availability of nesting sites, dominant males favour a close-range defence of nesting sites, while subordinate males invest more in courtship activities. However, subordinate males often directed courtship movements towards a nesting site dominated by a concealed dominant male, who subsequently took over the female and resumed courtship. Our laboratory experiment also showed that only dominant males obtained spawning success regardless of the amount of effort allocated to courtship behaviour, circumventing the initial female preference for the subordinate male. Subordinate males were more likely to initiate contests and ceased courtship upon losing aggressive contests. In such instances, the courtship effort of dominant males was higher, suggesting that dominant males modulate their courtship effort according to the effort of subordinate males. We refer to this tactic as courtship piracy. For being dependent on resource defence, the effectiveness of courtship piracy is contingent on the defendability of nesting sites. In a follow-up experiment, we show that dominant males invest more in nesting site defence only when nesting sites are scarce. Since rainfall controls the amount of nesting sites in the natural habitat, we suggest that seasonality modulates the relative contribution of courtship piracy and female mate choice to reproductive success.

Due to the importance of camouflage to avoid detection by predators, predation pressure can cause coupled evolution of skin colour and preference for substrate colour. Individuals can choose regions where the background makes their skin colour less noticeable (crypsis) or where it accentuates warning coloration (aposematism). In such scenario, individuals should optimally choose substrate according to their skin colour and mechanism of predation avoidance: toxic species are expected to choose highly lit places and non-toxic species should avoid such places. We studied substrate choice on five species of tadpoles that differ in body colour and toxicity. The results of the present study did not confirm our prediction that non-toxic and cryptically coloured species would prefer a lower contrast substrate that maximizes camouflage. We show that individuals preferred highly lit areas that accentuated their contrast with the substrate. The general preference for lighter substrate might be related to the tadpole’s limited vision on a dark substrate, which hampers their ability in detecting predators. This study demonstrates that tadpoles can distinguish the substrate colour and that their choice of habitat might be linked to both their defence mechanism in the case of aposematic species and recognition of habitat elements in the case of cryptically-coloured species.

Observacoes diretas em campo constituem uma importante fonte de informacoes sobre a historia natural e o comportamento de peixes de riacho. Contudo, tais observacoes diretas podem ser insuficientes para permitir conclusoes robustas sobre as causas dos fenomenos biologicos envolvidos, ja que dados observacionais frequentemente falham em demonstrar de forma contundente relacoes de causa e efeito. Neste estudo nos trazemos conceitos necessarios para a formulacao de hipoteses a partir de uma versao derivada da Historia Natural e da Etologia, a Ecologia Comportamental Evolutiva. Essa perspectiva permite analises do contexto evolutivo e do valor adaptativo dos padroes comportamentais observados, e serve de base para novas hipoteses que podem ser aplicadas a muitos grupos de organismos. Observacoes e experimentos envolvendo peixes de riacho originaram e deram subsidio a muitas teorias sobre a evolucao de comportamentos e de caracteristicas morfologicas peculiares que sao amplamente debatidas pela comunidade cientifica. Apos apresentar os conceitos chaves, nos trazemos alguns exemplos de programas de pesquisas com peixes que culminaram na formulacao de importantes teorias, onde cientistas aproveitaram as oportunidades que os peixes de riacho oferecem e conduziram observacoes, amostragens e experimentos controlados em campo e laboratorio. Descrevemos nosso programa de pesquisas, que tem uma especie amazonica de peixe de riacho (Crenuchus spilurus) como organismo modelo. Ao final, advogamos pela pluralidade de metodos e analises no estudo da Ecologia Comportamental Evolutiva de peixes de riacho. BEHAVIORAL EVOLUTIONARY ECOLOGY - WITH APPLICATIONS TO FRESHWATER STREAM FISH: Direct field observation constitutes an important source of information on life history and behavior of stream fish. Unfortunately, information gathered from direct field observations are often limited and thus may fail to provide robust testing for the causation of biological phenomena. Here, we bring concepts that form the theoretical foundation necessary for raising hypotheses in Evolutionary Behavioral Ecology, a study area directly derived from natural history and ethology that directly incorporates evolutionary processes and the adaptative value of behavioral patterns observed. This perspective allows the analysis of the evolutionary context and the adaptive value of observed behavioral patterns, and serves as the basis for new hypotheses that can be applied to many groups of organisms. Using this framework, field observations and experiments encompassing freshwater stream fish have subsidized many theories on the evolution of behavioral and morphological traits that are widespread debated by scientific community. After presenting the main key concepts, we bring some examples of research programs with freshwater fish that culminated in the formulation of important theories and where scientists took advantage of the opportunities provided by stream fish to conduct observations, samplings and controlled experiments both in the field and in captivity. We also describe our own research program, which uses an Amazonian freshwater stream fish (Crenuchus spilurus) as a model organism. By doing so, we advocate for the use of several methods and analyses for the study of Evolutionary Behavioral Ecology of freshwater stream fish.

A major component of Darwin's formulation of sexual selection theory is whether mate choice can contribute to the evolution of cognitive abilities. Although a correlation between cognition and attractive traits has commonly been reported, the processes that generate such associations remain elusive. Here, we investigated female preference, neophobia and spatial learning in the sailfin tetra, Crenuchus spilurus, a sexually dimorphic fish. Females chose the most ornamented males, which were also more neophobic. This is in line with the asset protection principle, which posits that attractive males should be more cautious because of their higher prospective fitness returns. After repeated exposure, more ornamented males learnt to navigate the complex maze faster, with chosen (and highest ornamented) males showing higher accuracy to solve the maze on the last day of trials. Because the asset protection principle stems from predation pressure, we propose that sexual selection through female mate choice creates a risk–reward trade-off, upon which natural selection acts by indirectly increasing learning abilities. As such, sexual selection forms the substrate, but natural selection drives enhanced cognitive abilities in attractive C. spilurus males.

The Amazon has the highest richness of freshwater organisms in the world, which has led to a multitude of hypotheses on the mechanisms that generated this biodiversity. However, most of these hypotheses focus on the spatial distance of populations, a framework that fails to provide an explicit mechanism of speciation. Ecological conditions in Amazon freshwaters can be strikingly distinct, as it has been recognized since Alfred Russel Wallace’s categorization into black, white, and blue (= clear) waters. Water types reflect differences in turbidity, dissolved organic matter, electrical conductivity, pH, amount of nutrients and lighting environment, characteristics that directly affect the sensory abilities of aquatic organisms. Since natural selection drives evolution of sensory systems to function optimally according to environmental conditions, the sensory systems of Amazon freshwater organisms are expected to vary according to their environment. When differences in sensory systems affect chances of interbreeding between populations, local adaptations may result in speciation. Here, we briefly present the limnologic characteristics of Amazonian water types and how they are expected to influence photo-, chemical-, mechano-, and electro-reception of aquatic organisms, focusing on fish. We put forward that the effect of different water types on the adaptation of sensory systems is an important mechanism that contributed to the evolution of fish diversity. We point toward underexplored research perspectives on how divergent selection may act on sensory systems and thus contribute to the origin and maintenance of the biodiversity of Amazon aquatic environments.

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 igarapes. Igarapes 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 igarape water on spawning and habitat choice in Crenuchus spilurus, a small fish composed of distinct genetic lineages that occur in igarapes flowing to blackwater and whitewater systems. Lineages from igarapes connected to the Rio Negro (blackwater) and Amazon River (whitewater) basins have greater spawning success in igarape water than in the water from their surrounding floodplain. Habitat choice trials showed active selection of igarape water by both lineages. Our results indicate that the hydrochemical condition of igarapes shapes adaptation in the physiology and behavior of C. spilurus. We suggest expanding upon the current classification to include igarapes as a distinct water type and environment.

Seasonal environments favor the evolution of capital breeding, whereby reproduction uses surplus energy from resources acquired during an earlier period. Consequently, reproductive effort in capital breeders is expected to depend on traits associated with energy storage rather than environmental conditions at the time of reproduction. Based on a 15-year dataset, we investigate the effect of phenotype (body size and condition) and environmental conditions (intensity of hydrological seasons, predator density, and density of conspecifics) on fecundity three capital breeding fish species from the strongly seasonal Amazon River floodplain: Psectrogaster rutiloides, Triportheus angulatus, and Acestrorhynchus falcirostris. Fecundity of all three species was strongly correlated with phenotype and modulated by unfavorable environmental conditions during the period of reproduction, especially high density of conspecifics. Fecundity was negatively affected by the density of conspecifics for small females of A. falcirostris, and for T. angulatus females with poor body condition. Fecundity of P. rutiloides declined during periods of drought when density of conspecifics was highest. A clear tradeoff between quantity and quality of oocytes was found only for P. rutiloides. This study highlights that reproductive allocation of capital breeders in seasonal environments is strongly linked to environmental conditions before and during the reproductive period.

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., Measurement(s)Diversity • Fish • spatial patternTechnology Type(s)digital curationFactor Type(s)geographic locationSample Characteristic - OrganismfishSample Characteristic - Environmentdrainage basinSample Characteristic - LocationAmazon Basin Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.11920800

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.

The cichlid Mesonauta festivus is common and abundant among macrophyte stands along a large geographical range of the Amazonas and Parana-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.

Combined effects of climate change and deforestation have altered precipitation patterns in the Amazon. This has led to changes in the frequency of extreme events of flood and drought in recent decades and in the magnitude of the annual flood pulse, a phenomenon that influences virtually all aspects of river-floodplain ecosystem dynamics. Analysis of long-term data revealed abrupt and synchronous changes in hydrology and fish assemblage structure of a floodplain lake near the confluence of Amazon and Negro rivers. After an intense drought in 2005, the assemblage assumed a different and fairly persistent taxonomic composition and functional structure. Declines in abundance after 2005 were more pronounced for species of all sizes having equilibrium life history strategy, large species with periodic life history strategy, and for all trophic levels except primary consumers. Our results suggest that the extreme drought triggered changes in the fish assemblage and subsequent anomalous hydrological conditions have hampered assemblage recovery. These findings stress the need to account for climatic-driven hydrological changes in conservation efforts addressing aquatic biodiversity and fishery resources in the central Amazon.

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.O peixe-pregador Gobiesox barbatulus apresenta atividade alimentar noturna, permanecendo estacionário e aderido à parte inferior de pedras durante a maior parte do dia. Para se alimentar utiliza as táticas de espreita e consumo de material particulado. Apresenta hábito alimentar carnívoro e ingere principalmente crustáceos bentônicos. Locomove-se principalmente de duas formas: (1) "pedra-a-pedra", deslizando seu disco adesivo ventral por sobre pedras adjacentes e (2) "surfe", quando se aproveita da energia da maré vazante para percorrer rapidamente distâncias de até quatro vezes seu tamanho. A época reprodutiva desta espécie ocorre entre o final da primavera e início do verão, quando deposita aproximadamente 2.000 ovos adesivos de 1 mm de diâmetro cada e dispostos em uma única camada na parte inferior de pedras. Possui mais de uma desova por estação reprodutiva e, portanto, contendo ovos em diferentes estágios de desenvolvimento. Realiza ventilação, limpeza e guarda dos ovos como formas de cuidado parental. Os dados aqui apresentados também indicam que G. barbatulus possui certa fidelidade aos locais nos quais se abriga, sendo provavelmente uma espécie territorial.

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 Conservação