Muted responses to heat in a nocturnal tropical rodent

We measured the thermoregulatory characteristics of a common, tropical murid rodent, Sundamys muelleri. Subcutaneous body temperatures and evaporative water loss increased at ambient temperatures above 33°C, but no increases in metabolic rate were observed as high as 38.2°C, indicating tropical rodents may be resilient as climate change progresses. Abstract in Malay is available with online material.     

Effects of long-term ozone exposure on citrus: Chlorophyll a fluorescence and gas exchange

Three-years-old trees of Satsuma mandarin (Citrus unshiu [Mak.] Marc.) cv. Okitsu were exposed to O₃ fumigation during long term (one year) in open-top chambers. As a result of the treatment, chlorophyll a fluorescence and gas exchange parameters were modified with respect to trees growing in O₃-free conditions. Net photosynthetic rate and stomatal conductance decreased and intercellular CO₂ concentration increased according to a reduction of the non-cyclic electron flow and a lower capacity to reduce the quinone pool. O₃ also reduced the development of non-photochemical quenching preventing the dissipation of excess excitation energy and, therefore, generated several alterations in photosynthetic apparatus. All these effects were obtained in long-term exposure and higher O₃ concentration. In O₃ ambient conditions, the effects were minor.     

Analytical and numerical analyses of the micromechanics of soft fibrous connective tissues

State of the art research and treatment of biological tissues require accurate and efficient methods for describing their mechanical properties. Indeed, micromechanics-motivated approaches provide a systematic method for elevating relevant data from the microscopic level to the macroscopic one. In this work, the mechanical responses of hyperelastic tissues with one and two families of collagen fibers are analyzed by application of a new variational estimate accounting for their histology and the behaviors of their constituents. The resulting close-form expressions are used to determine the overall response of the wall of a healthy human coronary artery. To demonstrate the accuracy of the proposed method, these predictions are compared with corresponding 3D finite element simulations of a periodic unit cell of the tissue with two families of fibers. Throughout, the analytical predictions for the highly nonlinear and anisotropic tissue are in agreement with the numerical simulations.     

Density-dependent habitat selection alters drivers of population distribution in northern Yellowstone elk

Although it is well established that density dependence drives changes in organismal abundance over time, relatively little is known about how density dependence affects variation in abundance over space. We tested the hypothesis that spatial trade-offs between food and safety can change the drivers of population distribution, caused by opposing patterns of density-dependent habitat selection (DDHS) that are predicted by the multidimensional ideal free distribution. We addressed this using winter aerial survey data of northern Yellowstone elk (Cervus canadensis) spanning four decades. Supporting our hypothesis, we found positive DDHS for food (herbaceous biomass) and negative DDHS for safety (openness and roughness), such that the primary driver of habitat selection switched from food to safety as elk density decreased from 9.3 to 2.0 elk/km². Our results demonstrate how population density can drive landscape-level shifts in population distribution, confounding habitat selection inference and prediction and potentially affecting community-level interactions.     

Two complementary perspectives on inter-individual genetic distance

This paper examines population structure through the prism of pairwise genetic distances. Two complementary perspectives, framed as two simple questions, are explored: Q1: What is the probability that a random pair of individuals from the same local population is more genetically dissimilar than a random pair from two distinct populations? Q2: On average, how genetically different are two individuals from the same local population, in comparison with two individuals chosen from any two distinct populations? Models are developed to provide quantitative answers for the two questions, given allele frequencies across any number of markers from two diploid populations. The probability from Q1 is shown to drop to zero with increasing number of genetic markers even for very closely-related populations and rare alleles. The average genetic dissimilarity of two individuals from distinct populations diverges from the average dissimilarity of two individuals from the same population by a percentage dependent on estimates of population differentiation. This perspective also suggests a measure of population distance based on the intuitive notion of pairwise genetic distance, along with a simple method of estimation. Results from recent empirical research on inter-individual genetic distance in human populations are analyzed in the context of the theoretical framework.     

Sexual and asexual development: two distinct programs producing the same tunicate

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Trace Element Concentration in Hair Samples as an Indicator of Exposure of Population in the Negev, Israel

The concentration of the toxic elements Ag, As, Cd, Co, Mn, Mo, Pb, Se, and U and the elements Al, Mg, Cu, Fe, and Zn in human hair samples of population living in the north of the Negev Desert in Israel was determined. The study population consisted of three subgroups: Jewish urban population, Bedouin urban population, and Bedouins living in unrecognized villages (the “dispersion”). The main focus is on the differences between these subgroups in an attempt to explore factors responsible for the variation in trace metal contents in hair samples. The results show that the level of several elements, particularly Ag, Mn, and Pb, in the female Bedouin group significantly differed from the other groups in the study. Exploring the reasons for these differences, we concluded that the lifestyle of those women is the main cause. The female Bedouin subgroup is exposed to heavy metals from kitchen utensils, jewelry, and makeup. Therefore, differences in the heavy metal concentration in the hair samples of this group were attributed to the traditional unique lifestyle and social behavior of the females in the Bedouin society.     

Improvement of mechanical and biological properties of freeze-dried denitrifying alginate beads by using starch as a filler and carbon source

Freeze-dried, alginate-based beads, used for the immobilization of a denitrifying bacterium (Pseudomonas sp.), were filled with different concentrations (10%, 20%, 30% and 40%, w/w) of granular starch. The beads were incubated under denitrifying conditions in laboratory-scale, flow-through columns and monitored for changes in their physical and denitrifying properties. Freeze-dried beads containing high concentrations of starch were found to have better mechanical and denitrifying properties than beads containing low concentrations of this filler. Nitrate removal by the beads was found to be correlated with their starch content. Nitrite accumulation, as a result of incomplete denitrification, increased with the decrease in starch content of the beads. Nitrite in the outlet of the columns was measured in all types of beads during the initial phase of incubation but was undetectable, with the exception of beads with the lowest starch content, at later stages of incubation. Received: 9 November 1998 / Received revision: 3 February 1999 / Accepted: 5 February 1999     

Leptin receptor-expressing pericytes mediate access of hypothalamic feeding centers to circulating leptin

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