Species distribution is strongly driven by local and global gradients in water availability but the underlying mechanisms are not clear. Vulnerability to xylem embolism (P 50 ) is a key trait that indicates how species cope with drought and might explain plant distribution patterns across environmental gradients. Here we address its role on species sorting along a hydrotopographical gradient in a central Amazonian rainforest and examine its variance at the community scale.We measured P 50 for 28 tree species, soil properties and estimated the hydrological niche of each species using an indicator of distance to the water table (HAND).We found a large hydraulic diversity, covering as much as 44% of the global angiosperm variation in P 50 . We show that P 50 : contributes to species segregation across a hydrotopographic gradient in the Amazon, and thus to species coexistence; is the result of repeated evolutionary adaptation within closely related taxa; is associated with species tolerance to Ppoor soils, suggesting the evolution of a stress-tolerance syndrome to nutrients and drought; and is higher for trees in the valleys than uplands.The large observed hydraulic diversity and its association with topography has important implications for modelling and predicting forest and species resilience to climate change.

The number of oocytes recovered from Bos taurus indicus females subjected to ovum pick-up averaged two to four times greater compared to Bos taurus taurus females. The objective of the present study was to test the hypothesis that this difference in oocyte yield was due to more preantral follicles in the ovaries of Bos indicus females. Ovaries (n = 64) from Nelore (Bos indicus) fetuses (n = 10), heifers (n = 12), and cows (n = 10), and Aberdeen Angus (Bos taurus) fetuses (n = 10), heifers (n = 12), and cows (n = 10) were cut longitudinally into halves, fixed, and processed for histological evaluation. The number of preantral follicles was estimated by counting them in each histological section, using the oocyte nucleus as a marker and employing a correction factor. The average number of preantral follicles in the ovaries of Bos indicus vs Bos taurus was (mean ± SD) 143,929 ± 64,028 vs 285,155 ± 325,195 for fetuses, 76,851 ± 78,605 vs 109,673 ± 86,078 for heifers, and 39,438 ± 31,017 vs 89,577 ± 86,315 for cows (P > 0.05). The number of preantral follicles varied greatly among individual animals within the same category, as well as between breeds. In conclusion, we inferred that the higher oocyte yield from Bos indicus females was not due to a greater ovarian reserve of preantral follicles. Therefore, mechanisms controlling follicle development after the preantral stage likely accounted for differences between Bos indicus and Bos taurus females in number of oocytes retrieved at ovum pick-up.

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SummaryThe objective of this study was to evaluate the effects of adding ascorbic acid to the media for in vitro culture of cattle ovarian fragments and to determine their effects on growth activation and viability of early-stage follicles. The ovarian cortex was divided into small fragments; one fragment was immediately fixed (control) and the other fragments were cultured in minimum essential medium (MEM) supplemented or not with various doses of ascorbic acid. Ovarian tissue was processed for histology, transmission electron microscopy (TEM) and immunohistochemical demonstration of proliferating cell nuclear antigen (PCNA). Compared with control fragments, the percentage of primordial follicles was reduced (p < 0.05) and the percentage of growing follicles had increased (p < 0.05) in cultured cortical fragments, independent of the tested medium or incubation time. Furthermore, compared with control tissue, culture of ovarian cortex for 8 days reduced the percentages of healthy, viable follicles (p < 0.05), but not when cultures were supplemented with 25, 50 or 100 g/ml of ascorbic acid. Ultrastructural and immunohistochemical analysis of 8 day cultured ovarian cortical fragments, however, showed the integrity and viability of follicles only when fragments were cultured in presence of 50 g/ml of ascorbic acid. In conclusion, this study demonstrated that addition of ascorbic acid to MEM at a concentration of 50 g/ml not only stimulates the activation of 8 day in vitro cultured cattle primordial follicles and subsequent growth of activated follicles, but also safeguards the viability of these early-stage follicles.

The development of culture systems to support the initiation of growth of primordial follicles is important to the study of the factors that control the earliest stages of folliculogenesis. The aims of the present study were to investigate the effects of α-tocopherol on survival, activation, and growth of cattle preantral follicles using histological and immunohistochemistry proliferating cell nuclear antigen (PCNA) studies. The ovarian cortex was divided into small fragments; one fragment was immediately fixed in Bouin (control). The other fragments were cultured for 2, 4, 6, or 8 d in culture plates with Minimum Essential Medium supplemented with insulin-transferrin-selenium (ITS), pyruvate, glutamine, hypoxanthine, BSA, and antibiotics (MEM+); and MEM+ plus α-tocopherol (5, 25, 50, 100, or 200 ng mL-1). Preantral follicles were classified according to their developmental stage (primordial, intermediate, primary, or secondary) and on the basis of morphological features (normal or degenerated). Pair-wise comparisons were done using Tukey’s procedure. Chi-square test was used to compare the percentage of follicles with PCNA-positive granulosa cells. All analyses were done with the SAS software (SAS Institute, Cary, NC, USA), and P < 0.05 was considered significant. The results showed that, compared with non-cultured cortical tissue (Day 0), the culture of ovarian tissue significantly reduced (P < 0.05) the percentage of normal follicles in all media tested, except for tissue cultured in the presence of 200 ng mL-1 of a-tocopherol. Furthermore, in all media tested, the percentage of primordial follicles was significantly reduced (P < 0.05), with a concomitant increase in the percentage of developing follicles. The highest percentage of secondary follicles was observed after 6 days of culture in MEM plus 200 ng mL-1 of a-tocopherol. The PCNA analysis confirmed the viability of follicles cultured with 200 ng mL-1 of a-tocopherol after 6 d. After 8 days of in vitro culture, we observed severe follicular degeneration in all media tested, suggesting that other supplements are recommended for longer periods of culture. In conclusion, the results of the present study indicate that 200 ng mL-1 of a-tocopherol maintains the survival of cattle preantral follicles and promotes activation of primordial follicles after 6 days of in vitro culture. Financial support: L. A. Lisboa is a recipient of CAPES support; E. R. Andrade and A. A. Alfieri are recipients of PRODOC/CAPES fellowships.