The commercial bark harvest of the African cherry (Prunus africana) on Mount Oku, Cameroon: Effects on traditional uses and population dynamics

Bark extracts of the African cherry (Prunus africana) are used to treat benign prostatic hyperplasia. This study examined the effects of commercial bark harvest on population dynamics in the Kilum-Ijim Forest Preserve on Mount Oku, Cameroon and on traditional uses. P. africana is valued for its timber and as fuel although its greatest value is as a traditional medicine for human and animal ailments. Harvest has depleted the resource and has eroded traditional forest protection practices. I constructed matrix models to examine the effects of bark harvest on population structure and on population dynamics in harvested and unharvested populations. Harvesting simulations examined the effect on the population growth rate (λ) with differing levels of mortality of harvest-sized and large trees and differing harvest frequencies. Size class frequencies for the entire forest decreased in a reverse j-shaped curve, indicating adequate recruitment in the absence of harvest. Individual plots showed differences from the overall forest data, suggesting effects of natural and man-made perturbations, particularly due to bark harvest. One plot (harvested in the 1980s) showed a temporal difference in λ and fluctuated around one, due to alternating high and low fruiting years; other unharvested plots showed smaller temporal differences. Harvested plots (harvested illegally in 1997) had values of λ less than one and showed small temporal differences. The control plot also showed λ less than one, due to poor recruitment in the closed canopy forest. The value of λ for the combined data was 0.9931 suggesting a slightly declining population. The elasticity matrix for the combined data indicated the population growth rate was most sensitive to the survival of the large reproductive trees (42.5% of the elasticity). In perturbation analyses, reducing the survival of the large trees caused the largest reductions in λ. Simulations involving harvesting frequency indicated λ returns to pre-harvest conditions if trees are re-harvested after 10–15 years, but only if the large trees are left unharvested. Management scenarios suggest harvest can be sustainable if seedlings and small saplings are planted in the forest and actively managed, although large-scale plantations may be the only feasible option to meet market demand. ^

Life history trade-offs and community dynamics of small fishes in a seasonally pulsed wetland

We used a one-dimensional, spatially explicit model to simulate the community of small fishes in the freshwater wetlands of southern Florida, USA. The seasonality of rainfall in these wetlands causes annual fluctuations in the amount of flooded area. We modeled fish populations that differed from each other only in efficiency of resource utilization and dispersal ability. The simulations showed that these trade-offs, along with the spatial and temporal variability of the environment, allow coexistence of several species competing exploitatively for a common resource type. This mechanism, while sharing some characteristics with other mechanisms proposed for coexistence of competing species, is novel in detail. Simulated fish densities resembled patterns observed in Everglades empirical data. Cells with hydroperiods less than 6 months accumulated negligible fish biomass. One unique model result was that, when multiple species coexisted, it was possible for one of the coexisting species to have both lower local resource utilization efficiency and lower dispersal ability than one of the other species. This counterintuitive result is a consequence of stronger effects of other competitors on the superior species.

Conformational dynamics associated with ligand binding to vertebrate hexa-coordinate hemoglobins

Neuroglobin (Ngb) and cytoglobin (Cygb) are two new additions to the globin family, exhibiting heme iron hexa-coordination, a disulfide bond and large internal cavities. These proteins are implicated in cytoprotection under hypoxic-ischemic conditions, but the molecular basis of their cytoprotective function is unclear. Herein, a photothermal and spectroscopic study of the interactions of diatomic ligands with Ngb, Cygb, myoglobin and hemoglobin is presented. The impact of the disulfide bond in Ngb and Cygb and role of conserved residues in Ngb His64, Val68, Cys55, Cys120 and Tyr44 on conformational dynamics associated with ligand binding/dissociation were investigated. Transient absorption and photoacoustic calorimetry studies indicate that CO photo-dissociation from Ngb leads to a volume expansion (13.4±0.9 mL mol-1), whereas a smaller volume change was determined for Ngb with reduced Cys (ΔV=4.6±0.3 mL mol-1). Furthermore, Val68 side chain regulates ligand migration between the distal pocket and internal hydrophobic cavities since Val68Phe geminate quantum yield is ∼2.7 times larger than that of WT Ngb. His64Gln and Tyr44Phe mutations alter the thermodynamic parameters associated with CO photo-release indicating that electrostatic/hydrogen binding network that includes heme propionate groups, Lys 67, His64, and Tyr 44 in Ngb modulates the energetics of CO photo-dissociation. In Cygb, CO escape from the protein matrix is fast (< 40 ns) with a ΔH of 18±2 kcal mol-1 in Cygbred, whereas disulfide bridge formation promotes a biphasic ligand escape associated with an overall enthalpy change of 9±4 kcal mol-1. Therefore, the disulfide bond modulates conformational dynamics in Ngb and Cygb. I propose that in Cygb with reduced Cys the photo-dissociated ligand escapes through the hydrophobic tunnel as occurs in Ngb, whereas the CO preferentially migrates through the His64 gate in Cygbox. To characterize Cygb surface 1,8-ANS interactions with Cygb were investigated employing fluorescence spectroscopy, ITC and docking simulations. Two 1,8-ANS binding sites were identified. One binding site is located close to the extended N-terminus of Cygb and was also identified as a binding site for oleate. Furthermore, guanidinium hydrochloride-induced unfolding studies of Cygb reveal that the disulfide bond does not impact Cygb stability, whereas binding of cyanide slightly increases the protein stability.