ABSTRACT
We described the feeding habits of Colomesus asellus from riverbanks of the upper-middleTocantins River, Central Brazil. Two sampling expeditions were carried out in August (dry season) and inOctober (rainy season) of 2013, downstream from the Lajeado Hydroelectric Power Plant, Tocantins state.The diet of C. asellus was characterized and compared between juveniles and adults and betweenindividuals captured in the dry season and in the rainy season. Individuals exhibited marked temporalsegregation, with a predominance of adults on the riverbanks during the dry season and the predominanceof juveniles in the rainy season. The diet of this species was based on diverse benthic prey, mostlyEphemeroptera nymphs (Insecta). Contrary to our expectations, the diet composition of C. asellus was notinfluenced by seasonal changes or ontogenetic factors, but the size of individuals determined the numberof prey consumed. Thus, C. asellus can be classified in its trophic ecology as an insectivore without relationwith fish size and seasonality.
Descrevemos os hábitos alimentares de Colomesus asellus capturados nas margens do rioTocantins, Brasil Central. Duas expedições de coleta foram realizadas em agosto (estação seca) e emoutubro (estação chuvosa) de 2013, a jusante da Usina Hidrelétrica de Lajeado, Estado do Tocantins. Adieta de C. asellus foi caracterizada e comparada entre juvenis e adultos e entre indivíduos capturados naestação seca e na estação chuvosa. Os indivíduos apresentaram marcada segregação temporal, compredominância de adultos nas margens do rio durante a estação seca e predominância de juvenis na estaçãochuvosa. A dieta desta espécie foi baseada em diversas presas bentônicas, principalmente ninfas deEphemeroptera (Insecta). Contrariamente às nossas expectativas, a composição da dieta de C. asellus não foiinfluenciada por mudanças sazonais ou fatores ontogenéticos, mas o tamanho dos indivíduos determinou onúmero de presas consumidas. Assim, a espécie pode ser classificada como insetívora, sem variação em suaecologia trófica relacionada à sazonalidade do ambiente ou ao seu tamanho.
Subject(s)
Animals , Feeding Behavior , Tetraodontiformes/genetics , Tetraodontiformes/metabolism , SeasonsABSTRACT
Cytogenetic analyses carried out in eight specimens of Sphoeroides spengleri revealed the presence of 2n = 46 chromosomes (20 M/SM and 26 ST/A). Besides the standard karyotypical set, the presence of B microchromosomes was observed in two individuals, ranging from 0 to 2 microchromosomes per cell. A karyotype composed by 2n = 46 chromosomes with occurrence of M and SM chromosomes is considered basal for the species from the clade comprising the families Tetraodontidae, Balistidae, and Diodontidae, although it represents a derived condition for the order Tetraodontiformes, whose basal karyotype would be composed by 2n = 48 acrocentric chromosomes. The occurrence of B microchromosomes in marine Tetraodontiformes fish was not known, and this represents the first report of such a chromosomal type.
Subject(s)
Animals , Cytogenetic Analysis , Tetraodontiformes/genetics , Chromosome Aberrations , Karyotyping , Fishes/geneticsABSTRACT
Nuclear hormone receptors (NRs) form a large superfamily of ligand-activated transcription factors, which regulate genes underlying a wide range of (patho) physiological phenomena. Availability of the full genome sequence of Tetraodon nigroviridis facilitated a genome wide analysis of the NRs in fish genome. Seventy one NRs were found in Tetraodon and were compared with mammalian and fish NR family members. In general, there is a higher representation of NRs in fish genomes compared to mammalian ones. They showed high diversity across classes as observed by phylogenetic analysis. Nucleotide substitution rates show strong negative selection among fish NRs except for pregnane x receptor (PxR), estrogen receptor (ER) and liver x receptor (LxR). This may be attributed to crucial role played by them in metabolism and detoxification of xenobiotic and endobiotic compounds and might have resulted in slight positive selection. Chromosomal mapping and pairwise comparisons of NR distribution in Tetraodon and humans led to the identification of nine syntenic NR regions, of which three are common among fully sequenced vertebrate genomes. Gene structure analysis shows strong conservation of exon structures among orthologoues. Whereas paralogous members show different splicing patterns with intron gain or loss and addition or substitution of exons played a major role in evolution of NR superfamily.