Assessing community and ecosystem sensitivity to climate change – toward a more comparative approach

Plant communities can vary widely in their sensitivity to changing precipitation regimes, as reported by Byrne et al., Mulhouse et al. and Sternberg et al. in this issue of Journal of Vegetation Science. But to understand why communities differ in their sensitivity, we argue that clearly defined metrics of sensitivity and coordinated research approaches are needed to elucidate mechanisms.     

Habitat selection and population regulation in temporally fluctuating environments

Understanding and predicting the distribution of organisms in heterogeneous environments lies at the heart of ecology, and the theory of density-dependent habitat selection (DDHS) provides ecologists with an inferential framework linking evolution and population dynamics. Current theory does not allow for temporal variation in habitat quality, a serious limitation when confronted with real ecological systems. We develop both a stochastic equivalent of the ideal free distribution to study how spatial patterns of habitat use depend on the magnitude and spatial correlation of environmental stochasticity and also a stochastic habitat selection rule. The emerging patterns are confronted with deterministic predictions based on isodar analysis, an established empirical approach to the analysis of habitat selection patterns. Our simulations highlight some consistent patterns of habitat use, indicating that it is possible to make inferences about the habitat selection process based on observed patterns of habitat use. However, isodar analysis gives results that are contingent on the magnitude and spatial correlation of environmental stochasticity. Hence, DDHS is better revealed by a measure of habitat selectivity than by empirical isodars. The detection of DDHS is but a small component of isodar theory, which remains an important conceptual framework for linking evolutionary strategies in behavior and population dynamics.     

Waardenberg syndrome (WS) type I is caused by defects at multiple loci, one of which is near ALPP on chromosome 2: First report of the WS consortium

Previous studies have localized the gene for Waardenburg syndrome (WS) type I to the distal portion of chromosome 2q, near the ALPP locus. We pooled linkage data obtained from 41 WS type I and 3 WS type II families which were typed for six polymorphic loci on chromosome 2q in order to refine the location of the WS locus (WS1) and evaluate the extent of genetic heterogeneity. In the course of this work, we developed diagnostic criteria for genetic and phenotypic studies. Our findings, based on two-locus and multilocus analysis using a linkage map established from reference pedigrees, suggest that there are two or more mutations causing WS, one of which (i.e., WS1) is located on chromosome 2q, between the ALPP and FN1 loci, at distances of 7.8 cM and 11.2 cM for each marker, respectively. The results also indicate that WS1 is responsible for the illness in approximately 45% of all families in this sample. However, the odds favoring this position over a location between ALPP and SAG are only 2:1 when alternate assumptions about the proportion of linked families are considered. We conclude that a more saturated map of this region of chromosome 2q, including highly polymorphic markers, will be needed to accurately distinguish linked families and, ultimately, isolate the mutant gene.     

Phylogeny of the New World true frogs (Rana)

Phylogenetic relationships among the species of true frogs (Rana) from North, South, and Central America were investigated based on the sequences of approximately 2 kb from the mitochondrial genome, sampled from most of the described species, as well as eight undescribed species. This analysis, combined with previous studies of the phylogeny of New World Rana, served as the basis for a revised classification of the group. The American species of Rana are not monophyletic; the western North American Amerana is more closely related to the R. temporaria group of Eurasia (together, these frogs form the group Laurasiarana). The remaining species from the Americas form the monophyletic group Novirana, which includes: R. sylvatica; Aquarana (the R. catesbeiana group); Ranula (the R. palmipes group, including the mostly upland Levirana species and the mostly lowland Lithobates species); Torrentirana (the R. tarahumarae group, or Zweifelia, plus R. sierramadrensis), Stertirana (the R. montezumae group, or Lacusirana, plus R. pipiens), Nenirana (the R. areolata group), and Scurrilirana (most of the southern and tropical leopard frogs). The mitochondrial sequences supported many of the previous hypotheses of relationships of New World Rana, although there were some differences involving the placement of the species R. pipiens, R. sierramadrensis, and R. sylvatica. Parametric bootstrap analyses indicated significant support for the relationships inferred from the mtDNA sequences, and rejected the previous hypotheses of relationships for these three species.     

A new bifunctional spin-label suitable for saturation-transfer EPR studies of protein rotational motion

A new bifunctional spin-label (BSL) has been synthesized that can be immobilized on the surface of proteins, allowing measurement of rotational motion of proteins by saturation-transfer electron paramagnetic resonance (STEPR). The spin-label contains a photoactivatable azido moiety, a cleavable disulfide, and a nitroxide spin with restricted mobility relative to the rest of the label. The label reacts with surface lysine residues modified with beta-mercaptopropionate. Bifunctional attachment is achieved by photoactivation of the azido group. Any spin-label that remains monofunctionally attached after photolysis is removed by reduction of the disulfide. Only bifunctionally attached BSL remains on the protein. Hemoglobin was used to test the utility of the BSL in STEPR by comparison with hemoglobin modified with maleimide spin-label (MSL), a commonly used standard for the STEPR technique. MSL is a monofunctional spin-label which is fortuitously immobilized by local protein structure within hemoglobin. The BSL labeling of hemoglobin did not significantly affect the quaternary structure of hemoglobin as determined by gel filtration chromatography. The conventional EPR spectra of the mono- and bifunctionally attached BSL-hemoglobin were similar to the MSL-hemoglobin spectrum, indicating that both forms of BSL were rigidly bound to hemoglobin. In contrast, the spectrum obtained by reaction of modified hemoglobin lysine residues with MSL indicated that these labels were highly mobile. The monofunctionally attached BSL was mobilized upon octyl glucoside addition whereas bifunctionally attached BSL was only slightly mobilized, suggesting that hydrophobic interactions immobilize the monofunctionally attached label on hemoglobin. The response of STEPR spectra of mono- and bifunctionally attached BSL-hemoglobin to changes in hemoglobin rotational correlation time was similar to the MSL-hemoglobin over the range of 10(-5)-10(-3) s. The spectra of bifunctionally attached BSL indicated slightly less motion than corresponding spectra for MSL or monofunctionally attached BSL. The new BSL is a good reporter of protein rotation and does not require unique protein structures for its immobilization on the protein. Thus, the BSL should be more generally applicable for STEPR studies of membrane protein rotation than existing monofunctional spin-labels.     

ULTRASTRUCTURE OF THE ZOOSPORES AND VEGETATIVE CELLS OF TETRAEDRON AND CHLOROTETRAEDRON (CHLOROPHYCEAE)1

The flagellar apparatus of the zoospores of Tetraedron bitridens Beck-Mannagetta and Chlorotetraedron polymorphum MacEntee, Bold et Archibald includes directly opposed basal bodies, a distal fiber that is elaborated into a ribbed structure to which the continuous striated microtubule-associated component (SMAC) is connected, and partial caps over the proximal end of each basal body. The angle between basal bodies ranges from approximately 25° to 150°. Basal bodies at wider angles are interconnected via their cores. A septum is present in the B-tubule of one basal body triplet in C. polymorphum. Both organisms have four microtubular rootlets arranged in a cruciate pattern. The two X-membered rootlets in a single cell have dissimilar numbers of microtubules. In C. polymorphum there are 5 and 6 microtubules in a 4/1 and 5/1 arrangement. 3/1 and 4/1 rootlets are present in T. bitridens. Zoospores of T. bitridens have a fuzzy coat whereas those of C. polymorphum are naked. Pyrenoids in both species are covered by a continuous starch sheath. Vegetative, interphase cells of C. polymorphum have two centrioles connected by a fiber that are located in depressions in the nuclear envelope. We propose that these two genera may be closely related to Neochloris, and that the coenobial genera Hydrodictyon, Pediastrum and Sorastrum are derived from a Tetraedron-like alga.     

Tunable Polyaniline‐Based Porous Carbon with Ultrahigh Surface Area for CO2 Capture at Elevated Pressure

Natural gas is the cleanest fossil fuel source. However, natural gas wells typically contain considerable amounts of CO₂, with on‐site CO₂ capture necessary. Solid sorbents are advantageous over traditional amine scrubbing due to their relatively low regeneration energies and non‐corrosive nature. However, it remains a challenge to improve the sorbent's CO₂ capacity at elevated pressures relevant to natural gas purification. Here, the synthesis of porous carbons derived from a 3D hierarchical nanostructured polymer hydrogel, with simple and effective tunability over the pore size distribution is reported. The optimized surface area reaches 4196 m² g^?1, which is among the highest of carbon‐based materials, with abundant micro‐ and narrow mesopores (2.03 cm³ g^?1 with d < 4 nm). This carbon exhibits a record‐high CO₂ capacity among reported carbons at elevated pressure (i.e., 28.3 mmol g^?1 total adsorption at 25 °C and 30 bar). This carbon also shows good CO₂/CH₄ selectivity and excellent cyclability. Molecular simulations suggest increased CO₂ density in micro‐ and narrow mesopores at high pressures. This is consistent with the observation that these pores are mainly responsible for the material's high‐pressure CO₂ capacity. This work provides insights into material design and further development for CO₂ capture from natural gas.