Environmental influence on the reproductive strategy of Helogenes marmoratus (Siluriformes: Cetopsidae) in the Amazonian streams

RESUMEN La estrategia reproductiva de una especie debe ajustarse a las variaciones de las condiciones ambientales para garantizar el equilibrio poblacional. En los riachos amazónicos de tierra firme las fluctuaciones hidrológicas están controladas principalmente por las lluvias locales, predominando especies de peces de pequeño porte. Investigamos la estrategia reproductiva de Helogenes marmoratus y la influencia de variables ambientales (e.g., lluvia, conductividad, descriptores del hábitat) en su actividad reproductiva. Colectamos mensualmente entre marzo de 2019 y marzo de 2020 en una microcuenca del río Guamá, en la Amazonia oriental brasileña. Identificamos un período reproductivo prolongado entre julio de 2019 y marzo de 2020. Los machos comienzan a reproducirse con un menor tamaño ( = 27.41; = 31.36 mm). Confirmamos desove parcial, baja fecundidad (59.55 ± 22.76 ovócitos) y ovócitos grandes (1.24 ± 0.15 mm). La estrategia reproductiva de H. marmoratus ocupa un lugar intermedio entre el gradiente oportunista y de equilibrio. Regresiones múltiples destacan la importancia de la profundidad, la conductividad eléctrica, los bancos de hojas y la lluvia como reguladores de la actividad reproductiva de las hembras, explicando 32% de la variación del IGS. Nuestro estudio proporciona evidencia de una respuesta reproductiva diferenciada entre los sexos a las variables ambientales.

ABSTRACT The reproductive strategy of a species must be adjusted to variations in environmental conditions to guarantee population balance. Hydrological fluctuations in Amazonian streams of terra firme (non-flooded) are controlled primarily by local rainfall. Fish assemblages are composed predominantly of species of small size. We investigated the reproductive strategy of the cryptic catfish Helogenes marmoratus and assessed the influence of environmental variables (e.g., rainfall, conductivity, habitat descriptors) on its reproductive activity in a catchment of the Guamá River in the eastern Brazilian Amazon. Through monthly collections between March 2019 and March 2020, we identified an extended reproductive period between July 2019 and March 2020. Males mature at smaller sizes than females ( = 27.41 mm; = 31.36 mm). We confirmed batch spawning, low fecundity (59.55 ± 22.76 stage IV oocytes), and large oocytes (1.24 ± 0.15 mm). Our results indicated that H. marmoratus strategy occupies an intermediate place between opportunistic and equilibrium gradient. Multiple regressions showed that thalweg depth, electrical conductivity, leaf litter, and rainfall are important drivers of reproductive activity of females of H. marmoratus, explaining 32% of the variation of the GSI. Our study provides evidence of differentiated reproductive response between the sexes to environmental variables.

Local effects of deforestation on stream fish assemblages in the amazon-savannah transitional area

The expansion of agriculture in the southeast Amazon-Savanah transitional area has greatly decreased forest cover and influenced stream structure and functioning. We assessed the effects of forest cover loss on the integrity of streams by assessing stream physical conditions and the taxonomic and functional diversity of fish assemblages in this transitional area. We hypothesize that low forest cover, especially adjacent to streams, results in poor physical conditions (e.g., warmer temperatures, less physical structure, etc.), which in turn will decrease the taxonomic and functional diversity of fish assemblages. We detected that loss of forest cover negatively affects natural stream conditions and reduces the functional diversity of fish assemblages, but we did not find a strong effect on taxonomic diversity. Ambush and stalking predators, diurnal surface pickers (groups that exhibit opportunistic life history strategies), grazers, pickers, and browsers (groups that exhibit equilibrium life history strategies) were the functional groups with the strongest relation to altered environments. These groups can explore different niches, both with natural characteristics or altered by human activities. Our results suggest that the preservation of riparian zones can minimize the loss of specialized fish species in assemblages of Amazon-Savannah stream systems.(AU)

A expansão da agricultura na área de transição Amazônia-Savana diminuiu muito a cobertura florestal, influenciando a estrutura e o funcionamento dos sistemas de riachos. Avaliamos o efeito da perda de cobertura florestal na integridade dos riachos avaliando as condições físicas do ambiente e a diversidade taxonômica e funcional das assembleias de peixes nesta área de transição. Nossa hipótese é que a baixa cobertura florestal, especialmente adjacente ao riacho, resulta em más condições físicas (por exemplo, temperaturas mais quentes, e menos estrutura física) o que por sua vez diminuirá os valores da diversidade taxonômica e funcional das assembleias de peixes. Detectamos que a perda de cobertura florestal afeta negativamente as condições naturais e reduz a diversidade funcional das assembleias de peixes, mas não encontramos um efeito para a diversidade taxonômica. Predadores de emboscada e espreita, catadores de superfície diurnos, pastores, catadores e navegadores foram os grupos funcionais que tiveram a relação mais forte com ambientes alterados. Esses grupos podem explorar diferentes nichos, tanto com características naturais quanto alterados pela ação antrópica. Nossos resultados sugerem a preservação da zona ripária a fim de evitar a perda de espécies especializadas das assembleias de peixes de riachos.(AU)

Rapid assessment of the ichthyofauna of the southern Guiana Shield tributaries of the Amazonas River in Pará, Brazil

The Northern Pará Drainage System encompasses the left-bank tributaries of the Amazonas River in the southern Guiana Shield region of Pará state, Brazil. Five of the region's state protected areas are considered strategic for the conservation of its biodiversity. In the present study, we assessed the ichthyofauna of the five state protected areas of the Northern Pará Drainage System. Seven expeditions were conducted between January 2008 and January 2009, which surveyed stretches of the Cuminá, Cuminapanema, Curuá, Jari, Mapuera, Nhamundá, and Paru rivers. These surveys yielded 286 species belonging to 38 families and eight orders, including seven new records of fish species for Brazil, six of which are also new records for the Amazon basin. Our results provide a valuable database for future research and conservation programs in the protected areas of the region. (AU)

The role of Lithodoras dorsalis (Siluriformes: Doradidae) as seed disperser in Eastern Amazon

Ichthyochory is an important process responsible for the high diversity of plant species in tropical flooded forests. Thus, this study aimed to investigate the role of a catfish species, Lithodoras dorsalis, as seed disperser in the flooded forests at the Amazon River mouth, Brazil. Analyzing the stomach contents of 371 individuals of Lithodoras dorsalis, the Germination Potential (GP%) and Germination Speed Index (GSI) of seeds that were removed intact were investigated. This allowed us to evaluate the germination performance of two important species of plants in Amazonia, Euterpe oleracea (Açaí) and Montrichardia linifera (Aninga), after passage through the digestive tract of this catfish species. Given that digestion by L. dorsalis reduced the germination viability of M. linifera and that seeds were often destroyed during consumption, we suggest that L. dorsalis may have a limited role as seed disperser of M. linifera and instead mostly act as seed predator. However, for the species E. oleracea, L. dorsalis was a potential disperser, since the performance of germination of these seeds was improved after digestion. In addition, the number of seeds consumed was directly proportional to the catfish's body size, reinforcing the role of doradids as potential seed dispersers in tropical forests.(AU)

A ictiocoria é um importante processo responsável pela alta diversidade de espécies vegetais nas florestas tropicais alagadas. Dessa forma, este trabalho teve como objetivo investigar o papel de Lithodoras dorsalis como dispersor de sementes na Foz Amazônica, Brasil. Analisando o conteúdo estomacal de 371 espécimes de Lithodoras dorsalis, o Potencial de Germinação (PG%) e o Índice de Velocidade de Germinação (IGS) de sementes removidas intactas foram investigados. Isto permitiu-nos avaliar o desempenho germinativo de duas importantes espécies de plantas na Amazônia, Euterpe oleracea (Açaí) e Montrichardia linifera (Aninga), após passagem pelo trato digestivo desta espécie de bagre. Dado que a digestão por L. dorsalis reduziu a viabilidade de germinação de M. linifera e que as sementes foram frequentemente destruídas durante o consumo, sugerimos que L. dorsalis tem um papel limitado como dispersor de sementes de M. linifera e, em vez disso, age como predador de sementes. No entanto, para a espécie E. oleracea, L. dorsalis foi um potencial dispersor, uma vez que o desempenho germinativo das sementes foi melhorado após a digestão. Além disso, o número de sementes consumidas foi diretamente proporcional ao tamanho corporal do bagre, reforçando o papel de doradídeos como potenciais dispersores de sementes em florestas tropicais.(AU)