The Role of Stochasticity in the Origin of Epigenetic Variation in Animal Populations.

Epigenetic mechanisms such as DNA methylation modulate gene expression in a complex fashion are consequently recognized as among the most important contributors to phenotypic variation in natural populations of plants, animals, and microorganisms. Interactions between genetics and epigenetics are multifaceted and epigenetic variation stands at the crossroad between genetic and environmental variance, which make these mechanisms prominent in the processes of adaptive evolution. DNA methylation patterns depend on the genotype and can be reshaped by environmental conditions, while transgenerational epigenetic inheritance has been reported in various species. On the other hand, DNA methylation can influence the genetic mutation rate and directly affect the evolutionary potential of a population. The origin of epigenetic variance can be attributed to genetic, environmental, or stochastic factors. Generally less investigated than the first two components, variation lacking any predictable order is nevertheless present in natural populations and stochastic epigenetic variation, also referred to spontaneous epimutations, can sustain phenotypic diversity. Here, potential sources of such stochastic epigenetic variability in animals are explored, with a focus on DNA methylation. To this day, quantifying the importance of stochasticity in epigenetic variability remains a challenge. However, comparisons between the mutation and the epimutation rates showed a high level of the latter, suggesting a significant role of spontaneous epimutations in adaptation. The implications of stochastic epigenetic variability are multifold: by affecting development and subsequently phenotype, random changes in epigenetic marks may provide additional phenotypic diversity, which can help natural populations when facing fluctuating environments. In isogenic lineages and asexually reproducing organisms, poor or absent genetic diversity can hence be tolerated. Further implication of stochastic epigenetic variability in adaptation is found in bottlenecked invasive species populations and populations using a bet-hedging strategy.

First Demonstration of Electrostatic Damping of Parametric Instability at Advanced LIGO.

Interferometric gravitational wave detectors operate with high optical power in their arms in order to achieve high shot-noise limited strain sensitivity. A significant limitation to increasing the optical power is the phenomenon of three-mode parametric instabilities, in which the laser field in the arm cavities is scattered into higher-order optical modes by acoustic modes of the cavity mirrors. The optical modes can further drive the acoustic modes via radiation pressure, potentially producing an exponential buildup. One proposed technique to stabilize parametric instability is active damping of acoustic modes. We report here the first demonstration of damping a parametrically unstable mode using active feedback forces on the cavity mirror. A 15 538 Hz mode that grew exponentially with a time constant of 182 sec was damped using electrostatic actuation, with a resulting decay time constant of 23 sec. An average control force of 0.03 nN was required to maintain the acoustic mode at its minimum amplitude.

Effects of transients in LIGO suspensions on searches for gravitational waves.

This paper presents an analysis of the transient behavior of the Advanced LIGO (Laser Interferometer Gravitational-wave Observatory) suspensions used to seismically isolate the optics. We have characterized the transients in the longitudinal motion of the quadruple suspensions during Advanced LIGO's first observing run. Propagation of transients between stages is consistent with modeled transfer functions, such that transient motion originating at the top of the suspension chain is significantly reduced in amplitude at the test mass. We find that there are transients seen by the longitudinal motion monitors of quadruple suspensions, but they are not significantly correlated with transient motion above the noise floor in the gravitational wave strain data, and therefore do not present a dominant source of background noise in the searches for transient gravitational wave signals. Using the suspension transfer functions, we compared the transients in a week of gravitational wave strain data with transients from a quadruple suspension. Of the strain transients between 10 and 60 Hz, 84% are loud enough that they would have appeared above the sensor noise in the top stage quadruple suspension monitors if they had originated at that stage at the same frequencies. We find no significant temporal correlation with the suspension transients in that stage, so we can rule out suspension motion originating at the top stage as the cause of those transients. However, only 3.2% of the gravitational wave strain transients are loud enough that they would have been seen by the second stage suspension sensors, and none of them are above the sensor noise levels of the penultimate stage. Therefore, we cannot eliminate the possibility of transient noise in the detectors originating in the intermediate stages of the suspension below the sensing noise.

Effects of long versus short bout exercise on fitness and weight loss in overweight females.

OBJECTIVE: The specific aim of this study was to determine if three 10 minute bouts of exercise per day (3 x 10) and two 15 minute bouts per day (2 x 15) were as effective as one 30 minute bout per day (1 x 30) for improving VO2 max and weight loss. METHODS: Overweight, female college students (body mass index > or = 28 kg/m2) were recruited and assessed at baseline and post-treatment for aerobic fitness (Astrand maximal cycle test), weight, skinfold thickness (7-site), and circumference measures (4-site). Following measurement of resting energy expenditure (REE), subjects were asked to follow a self-monitored calorie restricted diet (80% of REE) for the twelve week duration of the study and were assigned (non-random) to one of four treatment groups: 1) a nonexercising control group (control, n = 8), 2) a 30 minutes continuous exercise group (1 x 30, n = 12), 3) a 30 minutes accumulated exercise group (2 x 15, n = 10) and 4) a second 30 minutes accumulated exercise group (3 x 10, n = 8). The exercising subjects participated in aerobic exercise training at 75% of heart rate reserve three to five days per week with all exercise monitored. RESULTS: VO2 max increased significantly while weight, body mass index, sum of skinfolds, and sum of circumferences decreased significantly from baseline to post-treatment in the 1 x 30, 2 x 15 and the 3 x 10 groups, but not in the control group. A tertiary finding was that exercise participation did not differ among the exercising groups with regard to the average number of days per week. CONCLUSIONS: These results support the hypothesis that exercise accumulated in several short bouts has similar effects as one continuous bout with regard to aerobic fitness and weight loss during caloric restriction in overweight, young women.