Comparative life-history strategies in three Lebiasinidae (Characiformes) in a Rio Negro tributary, Brazilian Amazon.

Reproductive traits co-evolve and form successful life-history strategies adapted to the biology and environment of a particular taxon, maximizing offspring and species survival chances, therefore studies investigating differences in adaptive traits across different environments can enhance our understanding of the natural selection process and evolution. Herein, we address whether the reproductive strategies of phylogenetically closely related fishes are influenced by habitat predictability, using three species of the Lebiasinidae family as models. The predominance of larger and mature individuals during the flood season, with high waters characterized by smaller immature individuals, suggests a seasonal reproductive strategy for Nannostomus trifasciatus. Copella callolepis, which inhabits both habitats, also showed a single reproductive peak. However, compared to N. trifasciatus, this species displayed late spawning, restricted to the flood season, as indicated by the higher abundance of larger and mature individuals during this period and the presence of smaller (juveniles) and spawned individuals in the following season. The reproductive tactics observed in N. marginatus differed significantly from the single reproductive peak of the other species, as two reproductive peaks were observed: one during the flood season and another during the low water season. In conclusion, our study demonstrates that the environment strongly influences reproductive strategies for lebiasinids. N. marginatus, restricted to small water bodies, exhibited an opportunistic reproductive strategy, whereas the species inhabiting main rivers, N. trifasciatus and C. callolepis, exhibited a more seasonal strategy.

Chromosomal Rearrangements and Satellite DNAs: Extensive Chromosome Reshuffling and the Evolution of Neo-Sex Chromosomes in the Genus Pyrrhulina (Teleostei; Characiformes).

Chromosomal rearrangements play a significant role in the evolution of fish genomes, being important forces in the rise of multiple sex chromosomes and in speciation events. Repetitive DNAs constitute a major component of the genome and are frequently found in heterochromatic regions, where satellite DNA sequences (satDNAs) usually represent their main components. In this work, we investigated the association of satDNAs with chromosome-shuffling events, as well as their potential relevance in both sex and karyotype evolution, using the well-known Pyrrhulina fish model. Pyrrhulina species have a conserved karyotype dominated by acrocentric chromosomes present in all examined species up to date. However, two species, namely P. marilynae and P. semifasciata, stand out for exhibiting unique traits that distinguish them from others in this group. The first shows a reduced diploid number (with 2n = 32), while the latter has a well-differentiated multiple X1X2Y sex chromosome system. In addition to isolating and characterizing the full collection of satDNAs (satellitomes) of both species, we also in situ mapped these sequences in the chromosomes of both species. Moreover, the satDNAs that displayed signals on the sex chromosomes of P. semifasciata were also mapped in some phylogenetically related species to estimate their potential accumulation on proto-sex chromosomes. Thus, a large collection of satDNAs for both species, with several classes being shared between them, was characterized for the first time. In addition, the possible involvement of these satellites in the karyotype evolution of P. marilynae and P. semifasciata, especially sex-chromosome formation and karyotype reduction in P. marilynae, could be shown.

Do local environmental factors structure the trophic niche of the splash tetra, Copella arnoldi? A test in an Amazonian stream system

Environmental variation affects the availability of spatial and trophic resources in Amazonian streams and may be important factors structuring the diet of fishes. We analyzed the diet composition and trophic niche breadth of the lebiasinid splash tetra, Copella arnoldi, aiming to evaluate how environmental variation in Amazonian streams affects the species' trophic niche. Fish were captured and environmental factors were recorded in 20 streams in the Caxiuanã National Forest, in the eastern Amazon, in November 2010. We made a semi-quantitative analysis of stomach contents of 200 individuals. Copella arnoldi exhibited an omnivorous diet composed mainly of detritus and allochthonous invertebrates. Environmental variation (stream width, stream depth, canopy cover and flow) did not affect the diet composition or trophic niche breadth of the species, possibly due to the regional integrity of the forest within the boundaries of the protected area. Riparian cover probably minimizes the effect of the small-scale variations in food resources, thus leading to a locally homogeneous diet composition in the splash tetra C. arnoldi. (AU)

Do local environmental factors structure the trophic niche of the splash tetra, Copella arnoldi? A test in an Amazonian stream system / Fatores ambientais influenciam o nicho trófico do tetra Copella arnoldi? Um teste em um sistema lótico amazônico

Environmental variation affects the availability of spatial and trophic resources in Amazonian streams and may be important factors structuring the diet of fishes. We analyzed the diet composition and trophic niche breadth of the lebiasinid splash tetra, Copella arnoldi, aiming to evaluate how environmental variation in Amazonian streams affects the species trophic niche. Fish were captured and environmental factors were recorded in 20 streams in the Caxiuanã National Forest, in the eastern Amazon, in November 2010. We made a semi-quantitative analysis of stomach contents of 200 individuals. Copella arnoldi exhibited an omnivorous diet composed mainly of detritus and allochthonous invertebrates. Environmental variation (stream width, stream depth, canopy cover and flow) did not affect the diet composition or trophic niche breadth of the species, possibly due to the regional integrity of the forest within the boundaries of the protected area. Riparian cover probably minimizes the effect of the small-scale variations in food resources, thus leading to a locally homogeneous diet composition in the splash tetra C. arnoldi.(AU)

Variações ambientais afetam a disponibilidade de recursos espaciais e tróficos em igarapés amazônicos e podem ser fatores importantes estruturando a dieta de peixes. Analisamos a composição da dieta e a amplitude de nicho trófico do lebiasinídeo Copella arnoldi, tendo como objetivo avaliar como a variação ambiental em igarapés amazônicos afeta o nicho trófico da espécie. Indivíduos foram capturados e fatores ambientais foram medidos em 20 igarapés da Floresta Nacional de Caxiuanã, na Amazônia Oriental, em Novembro de 2010. Fizemos uma análise semi-quantitativa do conteúdo estomacal de 200 indivíduos. Copella arnoldi apresentou uma dieta onívora composta predominantemente por detritos e invertebrados alóctones. A variação ambiental (largura e profundidade do igarapé, cobertura de dossel e correnteza) não afetaram a composição da dieta ou a amplitude de nicho trófico da espécie, possivelmente devido à integridade regional da floresta na área protegida. A cobertura ripária provavelmente minimiza os efeitos da variação ambiental nos recursos tróficos, levando, assim, a uma dieta localmente homogênea de C. arnoldi.(AU)