Self-Replication Without Hydrogen-Bonds: An Exobiotic Design.

Life on Earth uses DNA as the central template for self-replication, genetic encoding, and information transfer. However, there are no physical laws precluding life's existence elsewhere in space, and alternative life forms may not need DNA. In the search for exobiology, knowing what to look for as a biosignature remains a challenge - especially if it is not from the obvious list of biologic building blocks.

Earthen mounds () of South Africa and their termite occupants: applicability of concepts of the extended phenotype, ecosystem engineering and niche construction.

are earthen mounds found throughout the Succulent Karoo of South Africa and are inhabited by the termite . Many have assumed that heuweltjies are constructed by the occupying termites. Consequently, heuweltjies have been used as an example of several important concepts in ecology and evolution: the , and .

Carbon isotope discrimination and foliar nutrient status of Larrea tridentata (creosote bush) in contrasting Mojave Desert soils.

We investigated the relationships between foliar stable carbon isotope discrimination (Delta), % foliar N, and predawn water potentials (psi(pd)) and midday stomatal conductance ( g(s)) of Larrea tridentata across five Mojave Desert soils with different age-specific surface and sub-surface horizon development and soil hydrologies. We wished to elucidate how this long-lived evergreen shrub optimizes leaf-level physiological performance across soils with physicochemical characteristics that affect the distribution of limiting water and nitrogen resources. We found that in young, coarse alluvial soils that permit water infiltration to deeper soil horizons, % foliar N was highest and Delta, g(s) and psi(pd) were lowest, while %N was lowest and Delta, g(s) and psi(pd) were highest in fine sandy soils; Larrea growing in older soils with well-developed surface and sub-surface horizons exhibited intermediate values for these parameters.

Prey refugia and the distributions of two Sonoran Desert cacti.

Two small Sonoran Desert cacti, Mammillaria microcarpa and Echinocereus englemannii, are commonly found beneath canopies of the larger, tree-like cactus Opuntia fulgida. The mechanism leading to this distribution pattern is incidental to the mode of reproduction in O. fulgida.

Sahuaro-nurse tree associations in the Sonoran Desert: competitive effects of sahuaros.

In the Sonoran Desert, the sahuaro cactus (Carnegiea gigantea) is commonly associated with canopies of trees and shrubs: so-called nurse plants. Although mechanisms by which nurse plants facilitate sahuaro establishment have been studied, possible competitive interactions between sahuaro cacti and nurse plants have not been conclusively demonstrated. In this paper I show that the close proximity of sahuaros leads to a relative increase in stem die-back as well as greater mortality in a common nurse tree, the foothill paloverde (Cercidium microphyllum).