System of automated gas-exchange analysis for the investigation of metabolic processes.

Conventional gas-exchange instruments are confined to the measurement of O(2) consumption (VO(2)) and CO(2) production (VCO(2)) and are subject to a variety of errors. This handicaps the performance of these devices at inspired O(2) fraction (FI(O(2))) > 0.40 and limits their applicability to indirect calorimetry only. We describe a device based on the automation of the Douglas bag technique that is capable of making continuous gas-exchange measurements of multiple species over a broad range of experimental conditions. This system is validated by using a quantitative methanol-burning lung model modified to provide reproducible (13)CO(2) production. The average error for VO(2) and VCO(2) over the FI(O(2)) range of 0.21-0.8. is 2.4 and 0.8%, respectively. The instrument is capable of determining the differential atom% volume of known references of (13)CO(2) to within 3.4%. This device reduces the sources of error that thwart other instruments at FI(O(2)) > 0. 40 and demonstrates the capacity to explore other expressions of metabolic activity in exhaled gases related to the excretion of (13)CO(2).     

Modelling of Aniline-Vermiculite and Tetramethylammonium-Vermiculite; Test of Force Fields

Molecular mechanics simulations in Cerius² have been used for modelling vermiculite intercalated with tetramethylammonium and aniline cations. The published structure data obtained for these intercalated structures from X-ray single crystal diffraction have been used to test the force fields and modelling strategy for organo-clays. The strategy of modelling was based on the nonbond host-guest interactions and on rigid silicate layers and rigid guest species. The rigidity of silicate layers requires that the cell parameters a, b and % are kept fixed during the energy minimisation. The energy term was set up using the nonbond interaction terms only and the Crystal Packer module in Cerius² has been used for the energy minimisation. In Crystal Packer the rigid units, i.e. the silicate layers and guest species can be translated and rotated during energy minimisation and the cell parameters c, !, and # have been varied. Three sets of Van derWaals (VDW) parameters available in Crystal Packer: Tripos, Universal and Dreiding have been used in present molecular simulations. Ab initio MP2 calculations were performed to justify the application of the force field. The best agreement of molecular mechanics simulations with both: experimental and ab initio data was obtained with the Tripos VDW parameters for both intercalates. The results of modelling are in good agreement with the experimental data as to the cell parameters and the interlayer packing. The cell parameters reported by Vahedi-Faridi and Guggenheim (1997) for tetramethylammonium-vermiculite are: c = 13.616 Å, ! = 90°, # = 97.68° ; from the present modelling we obtained: c = 13.609 Å, ! = 90.19°, # = 97.56°. Tetramethylammonium-cations are arranged in one layer in the interlayer space. One C-C edge of NC₄ tetrahedra is perpendicular to the silicate layers. The deep immersion of the methyl groups into the ditrigonal cavities suggested by Vahedi-Faridi and Guggenheim was not confirmed by modelling. Slade and Stone (1984) presented the measured cell parameters for aniline vermiculite: c = 14.89 Å, ! = 90°, # = 97°; present result is: c = 14.81 Å, ! = 90.72°, # = 96.70° for partially exchanged vermiculite and c = 14.84 Å, ! = 90.53°, # = 97.17° for fully exchanged vermiculite. The aniline cations are positioned over the ditrigonal cavities alternating in their anchoring to lower and upper silicate layer. The C-N bonds are perpendicular to layers.     

Burrow architecture,family composition and habitat characteristics of the largest social African mole-rat: the giant mole-rat constructs really giant burrow systems

Among African mole-rats, the giant mole-rat Fukomys mechowii is the largest social species. Despite several attempts to study a free-living population, information on its biology from natural habitats is very scarce. We mapped two neighbouring burrow systems of the giant mole-rat in a miombo woodland in Zambia. We provide information on the size and kin structure of the respective mole-rat families, architecture of their burrow systems, and characteristics of the food supply and soil around the two mapped and additional ten burrow systems. Both uncovered burrow systems were very large (total lengths, 2,245 and 743 m), making them the largest burrow systems ever mapped. Food resources around the additional ten burrow systems had a clumped distribution (standardized Morisita index of dispersion = 0.526), but a relatively high biomass (298 ± 455 g m⁻²). This, together with favourable soil conditions even in the advanced dry season (cone resistance, 328 ± 50 N m⁻²; soil density, 1.36 ± 0.06 g cm⁻³) indicates relatively hospitable ecological conditions. Both food supply and soil conditions were comparable with the conditions found in a miombo habitat of the solitary silvery mole-rat in Malawi. This suggests that there are no ecological constraints which would preclude the solitary life of a subterranean herbivore from the examined habitat. Microsatellite analysis supported the assumption that giant mole-rats live in monogamous multigenerational families with only one breeding pair of non-related animals and their offspring. The mean family size is consistent with previous findings on this species and comparable to that found in other Fukomys species studied thus far.     

Natural history and burrow system architecture of the silvery mole-rat from Brachystegia woodland

The silvery mole-rat Heliophobius argenteocinereus (Bathyergidae) is a solitary subterranean rodent, widely distributed throughout eastern and south-eastern Africa in a variety of habitats. Here, we provide the first data on its biology in a typical natural habitat, the Brachystegia woodland. The population density of mole-rats was low (4.6 ha⁻¹) and its distribution across the study site was random. Contrary to subadults and pups, the sex ratio of adult mole-rats was highly female biased (1:5.75), probably due to the higher mortality of males as a consequence of their mating strategy. Reproduction of Heliophobius is seasonal and pups are born at the beginning of the hot dry season. Burrow systems of the silvery mole-rat were long, highly branched, reticulated and comparable in fractal dimension to systems of social bathyergids. Variability in burrow architecture was related to the body mass of the burrow occupants, soil hardness and food supply when tested together. Burrow systems with a higher fractal dimension had inhabitants that had a greater body mass. Longer systems were less branched. Nests were typically deeper than foraging tunnels and experienced negligible temperature fluctuations. The microenvironmental characteristics of the subterranean niche including temperature, humidity and soil characteristics are provided for purpose of comparison with other mole-rat species.     

Molecular phylogeny of African hinged and helmeted terrapins (Testudines: Pelomedusidae: Pelusios and Pelomedusa)

Fritz, U., Branch, W. R., Hofmeyr, M. D., Maran, J., Prokop, H., Schleicher, A., ?iroký, P., Stuckas, H., Vargas‐Ramírez, M., Vences, M. & Hundsdörfer, A. K. (2010). Molecular phylogeny of African hinged and helmeted terrapins (Testudines: Pelomedusidae: Pelusios and Pelomedusa). —Zoologica Scripta, 40, 115–125. With 18 currently recognised species, Pelusios is one of the most speciose chelonian genera worldwide, even though the taxonomy of some species is contentious. Recent investigations suggested that the closely related, but morphologically distinct genus Pelomedusa is paraphyletic with respect to Pelusios, and that Pelomedusa consists of nine deeply divergent lineages. Using three mitochondrial and three nuclear DNA fragments (2054 bp mtDNA, 2025 bp nDNA), we examined for the first time the phylogeny of Pelusios by molecular means. Our analyses included all Pelusios species, except the probably extinct P. seychellensis, as well as the nine Pelomedusa lineages. The results showed that Pelusios and Pelomedusa are reciprocally monophyletic. Limited sampling of Pelusios species and homoplasy introduced by remote outgroups most likely explain the paraphyly of Pelomedusa in previous studies. The distinctiveness of most Pelusios species was confirmed, but none of the currently recognised species groups within Pelusios was monophyletic. In Pelusios rhodesianus and P. sinuatus distinct genetic lineages were discovered, suggestive of cryptic taxa. In contrast, the recognition of the weakly differentiated P. castaneus and P. chapini as full species is doubtful, as is the validity of the Malagasy and Seychellois subspecies of P. castanoides. GenBank sequences of P. williamsi were nested within P. castaneus, but the morphological distinctiveness of the two species makes it likely that the GenBank sequences (derived from a turtle from the pet trade) are misidentified. Divergence among the distinct genetic lineages of Pelomedusa equals or exceeds the differences among Pelusios species, supporting the view that Pelomedusa is a species complex.     

Cochlear hair-cell populations and limits of resolution of hearing in two vespertilionid bats,Nyctalus noctula and Eptesicus serotinus

A comparison of the population of cochlear hair cells with known hearing resolution capabilities in two species of bats (Nyctalus noctula and Eptesicus serotinus of the family Vespertilionidae) has revealed a close correlation between morphological and functional parameters. Data on number and densities of hair cells in the examined bat species are presented. Even though the species are of a comparable body size, N. noctula has a longer basilar membrane, a higher density, and hence also a higher total number of hair cells than E. serotinus. This is in good agreement with hearing resolution capabilities, which are better in N. noctula than in E. serotinus. These findings have implications on differences in feeding ecology and hunting strategies between these species.