Natural selection drives populations towards higher fitness, but crossing fitness valleys or plateaus may facilitate progress up a rugged fitness landscape involving epistasis. We investigate quantitatively the effect of subdividing an asexual population on the time it takes to cross a fitness valley or plateau. We focus on a generic and minimal model that includes only population subdivision i...

[1] Many landscapes are composed of ridges and valleys that are uniformly spaced, even where valley locations are not controlled by bedrock structure. Models of long-term landscape evolution have reproduced this phenomenon, yet the process by which uniformly spaced valleys develop is not well understood, and there is no quantitative framework for predicting valley spacing. Here we use a numeric...

The Dry Valleys are subdivided into three microclimate zones on the basis of summertime measurements of atmospheric temperature, soil moisture, relative humidity and wind-speed/ direction. Subtle variations in these climate parameters result in considerable differences in process geomorphology and in the development of unique landforms within each zone. The mapped zones include a coastal thaw z...

Terrain structure lines (valleys and ridges) are very important for geomorphological characterization, they construct the skeleton of terrain undation and variation, and they are scale-dependent because the ones are more important at a larger geographical scale than their counterparts at a smaller. Wavelet analysis is a new branch of mathematics burgeoning at the end of 80s. It has double meani...

Introduction: The likelihood that dissociating methane clathrate hydrate makes a significant contribution to martian atmospheric methane has been reported by [1-3]. The clathrate might be found in or beneath subsurface permafrost [1, 3-4], in surface ice such as glacial remnants [2], or, as reported here, in icy sediments. These reports suggest that triggers for clath-rate dissociation in recen...

Erosion by glacial and fluvial processes shapes mountain landscapes in a long-recognized and characteristic way. Upland valleys incised by fluvial processes typically have a V-shaped cross-section with uniform and moderately steep slopes, whereas glacial valleys tend to have a U-shaped profile with a changing slope gradient. We present a novel regional approach to automatically differentiate be...

Simple and ubiquitous gene interactions create rugged fitness landscapes composed of coadapted gene complexes separated by "valleys" of low fitness. Crossing such fitness valleys allows a population to escape suboptimal local fitness peaks to become better adapted. This is the premise of Sewall Wright's shifting balance process. Here we generalize the theory of fitness-valley crossing in the tw...