Changes in turbulent mixing shift competition for light between phytoplankton species

The intriguing impact of physical mixing processes on species interactions has always fascinated ecologists. Here, we exploit recent advances in plankton models to develop competition theory that predicts how changes in turbulent mixing affect competition for light between buoyant and sinking phytoplankton species. We compared the model predictions with a lake experiment, in which the turbulence structure of the entire lake was manipulated using artificial mixing. Vertical eddy diffusivities were calculated from the measured temperature microstructure in the lake. Changes in turbulent mixing of the lake caused a dramatic shift in phytoplankton species composition, consistent with the predictions of the competition model. The buoyant and potentially toxic cyanobacterium Microcystis dominated at low turbulent diffusivity, whereas sinking diatoms and green algae dominated at high turbulent diffusivity. These findings warn that changes in the turbulence structure of natural waters, for instance driven by climate change, may induce major shifts in the species composition of phytoplankton communities

Early menopause in mothers of children with Down syndrome?

Objective: To investigate whether having a Down syndrome pregnancy at a relatively young age is associated with lower ovarian reserve as reflected by lower antimullerian hormone (AMH) levels and the occurrence of earlier menopause. Design: Retrospective, case control study. Setting: Not applicable. Patient(s): Two hundred twenty mothers (118 trisomy cases, 102 controls). Intervention(s): Questionnaire and serum AMH measurement. Main Outcome Measure(s): Serum AMH levels and menopause, defined as not having a menstrual cycle for at least 1 year. Result(s): The participant response rate was 93%. After applying the exclusion criteria, 144 women were evaluable (73 trisomy cases, and 71 controls). The baseline characteristics of the women were not statistically significantly different. More women with a Down syndrome pregnancy had an AMH level below 0.5 mu g/L, a difference that was statistically significant. Eleven women (15.1%) in the Down syndrome group had reached menopause compared with 9 (12.7%) of the controls. Conclusion(s): Women who have had a Down syndrome pregnancy at a younger age show signs of limited ovarian reserve, as evidenced by their frequently having lower AMH levels. The study has found no obvious signs of early menopause thus far. Whether their age at menopause is within the normal range remains to be determined. (Fertil Steril (R) 2011; 96: 985-90. (C)2011 by American Society for Reproductive Medicine.