Federal University of Western Pará

Hydroelectric reservoirs are often responsible for releasing total mercury (THg) into aquatic ecosystems. There is limited information on the influence of hydrosystem gradients and fluvial regimes on THg distribution. This study aimed to investigate the influence of vertical gradients, hydrosystem gradients, and fluvial regime on THg distribution in water and plankton in the Curuá-Una reservoir, Brazilian Amazon. Samplings were carried out in four fluvial periods: low-water, rising-water, high-water, and falling-water periods. THg levels were determined by cold vapor atomic fluorescence spectroscopy. Physicochemical conditions of the reservoir varied between lacustrine, transition, and riverine zones. Water transparency was greatest in the lacustrine zone (2.5 m), where the depth reaches 18 m. Conductivity (46.8 μS cm^-1) and dissolved oxygen (7.7 mg L^-1) were higher in the riverine zone in the falling-water period. During the rising-water period, THg was higher in the hypolimnion (8.8 ng L^-1) than in the epilimnion (6.2 ng L^-1). THg increased in the low-water period (7.9 ± 1.2 ng L^-1). The results demonstrate the influence of water stratification, hypoxia, and fluvial regime on THg dynamics. In the low-water period, the hypoxic hypolimnion favored the increase in HgT. Hg release was also found to be influenced by deforestation and human activities, with higher concentrations observed in pasture and agricultural areas, affecting local aquatic biota. THg dynamics are influenced by hydrological and hydrometric processes. Therefore, these factors should be considered in environmental studies aimed at preserving Amazonian biodiversity.

Understanding embryonic and fetal development is fundamental to interpreting life-history strategies associated with neonatal survival in mammals. This study provides a detailed characterization of the intrauterine development of the hystricognath rodent, the black agouti (Dasyprocta fuliginosa), one of the most hunted species in the Amazon. The developmental patterns are compared with those of other precocial and altricial mammals, offering insights into species-specific reproductive strategies. A total of 90 conceptuses (2 embryos and 88 fetuses) from 49 pregnant females collected from subsistence hunting in the Peruvian and Brazilian Amazon were analyzed for external and internal morphological features. The mean prolificacy was 1.84 ± 0.59 offspring per pregnant female, with a sex ratio of 1.26:1.00 (female:male). Fetal dorsal length (TDL) ranged from 0.57 to 23.3 cm. External development followed a consistent and sequential pattern, beginning with the appearance of outer ears, eyelid and limb buds, followed by ossification, fused eyelids, tactile pelage, differentiated genitalia, skin development, covering pelage, nail formation, tooth eruption, and ultimately eyelid opening. Fetal age estimation, based on the formula ∛W = 0.078(t - 20.8), showed a strong correlation between TDL and gestational age. All external biometric measures and absolute visceral organ masses were strongly correlated with TDL. The relative mass of the spleen, the tubular digestive organs, and the thymus increased across pregnancy; while liver, lungs, and kidneys decreased. The developmental pattern observed supports the classification of the black agouti as a precocial species, with neonates exhibiting early functional independence.

The Colour Assessment and Diagnosis (CAD) and the Cambridge Colour Test (CCT) are computerized psychophysical tests widely used in the diagnosis of color vision deficiencies due to their high specificity and sensitivity. However, these tests differ substantially in the type of visual task, stimulus configuration, vectors, luminance, background composition, and presentation time. This study aimed to compare the evaluation parameters estimated by these tests in trichromatic and dichromatic individuals. A total of sixty-six participants (40 trichromats and 38 dichromat individuals -16 protans and 22 deutans; mean age: 26.3 ± 8.9 years) were evaluated. Color discrimination thresholds were fitted to elliptical functions, and parameters such as ellipse area, rotation angle, and the size of protan, deutan, and tritan vectors were analyzed. Results showed equivalence between the tests for: the deutan and tritan vector areas and sizes in the trichromat subgroup; tritan vector area and size in the protan subgroup; and protan and tritan vector sizes in the deutan subgroup. Differences in the central coordinates of the CAD and CCT tests and the spatial arrangement of vectors in the CIE 1976 color space (specific to the CCT test) may have influenced the results. Nonetheless, agreement was observed in the measures of ellipse area, rotation angle, and sizes of the protan and tritan vectors between the two tests. These findings suggest that, despite methodological differences, the CAD and CCT tests produce largely comparable results and can be considered complementary tools in the assessment of color discrimination in clinical and research settings.