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Facultative adjustment of sex ratios by mothers occurs in some animals, and has been linked to resource availability. In mammals, the search for consistent patterns is complicated by variations in mating systems, social hierarchies and litter sizes. Humans have low fecundity, high maternal investment and a potentially high differential between the numbers of offspring produced by sons and daughters: these conditions should favour the evolution of facultative sex ratio variation. Yet little is known of natural mechanisms of sex allocation in humans. Here, using data from 740 British women who were unaware of their foetus's gender, we show that foetal sex is associated with maternal diet at conception. Fifty six per cent of women in the highest third of preconceptional energy intake bore boys, compared with 45% in the lowest third. Intakes during pregnancy were not associated with sex, suggesting that the foetus does not manipulate maternal diet. Our results support hypotheses predicting investment in costly male offspring when resources are plentiful. Dietary changes may therefore explain the falling proportion of male births in industrialized countries. The results are relevant to the current debate about the artificial selection of offspring sex in fertility treatment and commercial ‘gender clinics’. [ABSTRACT FROM AUTHOR]

Previous studies have shown that functional capillary density (FCD) is substantially reduced by erythrocyte aggregation. However, only supranormal levels of aggregability were studied. To investigate the effect of erythrocyte aggregability at the level seen in healthy humans, the FCD of selected capillary fields in rat spinotrapezius muscle was determined with high-speed video microscopy under normal (nonaggregating) conditions and after induction of erythrocyte aggregation with Dextran 500 (200 mg/kg). To examine shear rate dependence, the effect was studied both at normal and reduced arterial pressures (50 and 25 mmHg), the latter achieved by short periods of hemorrhage. In a separate study, volume flow was determined in arterioles (52.1 ± 3.7 μm) under the same conditions. Before Dextran 500 infusion, FCD fell to 91% and 76% of control values, respectively, when arterial pressure was reduced to 50 and 25 mmHg. After Dextran 500 infusion, FCD was 96% at normal arterial pressure and fell to 79% and 37% of normal control values at 50 and 25 mmHg. All FCD values were significantly lower after dextran infusion. FCD reduction after lowering arterial pressure or dextran infusion appeared to be due to plasma skimming rather than capillary plugging. Reduction of FCD by dextran at reduced pressure was compensated by increased red blood cell flux in capillaries with red blood cell flow. We conclude that the level of aggregability seen in healthy humans is an important determinant of FCD only at reduced arterial pressure. [ABSTRACT FROM AUTHOR]

Bushmeat markets can reflect the impact of hunting in large geographical areas, but efficient and adequate sampling strategies are needed. Five bushmeat markets in West and Central Africa were used to simulate the performance of different sampling regimes. The studied markets (n = 863 days) varied in animal carcasses and number of species recorded. In our simulations, we varied number of days sampled and their temporal distribution using a variant of the Monte Carlo methodology. Three sample strategies were considered: (1) unconstrained random sampling; (2) random sampling of start-points, where the n days sampled are a sequential block following the randomly selected start-point and (3) sampling blocked by season. No substantial differences between standard sampling theory and our simulations were present. However, only a large sample of markets will allow useful inferences on a regional scale and timing and coordination of sampling may be highly influential. Sampling in blocks of days was as efficient as simple random sampling in estimating species richness, but not carcass volume. This may indicate that, even with seasonality in market compositions, or irregular influences, the temporal pattern as described by presence/absence varies much less than does the volume of carcasses. Shorter sampling periods perform poorly in estimating species richness. The relationship between % species richness and overall carcass volume may predict the sampling effort required to estimate market species richness based on volume, when a large enough sample of markets becomes available. Similarly, a larger sample of markets would reveal how far the species composition in markets reflects the general organising principles of community structure in terms of frequency and abundance relationships. [ABSTRACT FROM AUTHOR]

Transition probabilities of H2, HD, and D2 − electric dipole, − discrete-continuum magnetic dipole, and electric quadrupole transitions have been calculated using accurate energies and ro-vibrational wave functions obtained from precise ab initio potential energy curves. The predissociation rates of the () levels by direct and indirect spin–spin and spin–orbit coupling between − fine structure levels, have been also determined. The present investigation achieved good agreement with measured lifetimes of the fine structure levels without adjustment. A comparison of the calculated and observed lifetimes of metastable H2, HD, and D2 suggests that the − magnetic dipole and electric quadrupole transition moments underestimate the spontaneous emission rate of the metastable levels by ∼370 s−1. The measured and calculated lifetimes of H2, HD, and D2 fine structure levels are in very good agreement after the adjustment of 370 s−1 to the spontaneous decay rate of the − transition. The calculated energies, transition probabilities, and predissociation rates obtained in the present work, along with the state excitation function, are sufficient to determine the state emission cross section, the kinetic energy distribution of H(1s) atoms, and the energy deposition rate of the − excitation. In a previous investigation by Berg and Ottinger (1994 J. Chem. Phys. 100 8746), the authors were forced to insert a large scale factor into the predissociation rate in order to reconcile with measured lifetimes. Errors introduced in the approximations made in the previous investigations are discussed in the text. The H2 state has the second largest triplet state excitation cross section. Predissociation and spontaneous emission of the state plays an important role in the energy deposition of H2-dominated atmospheres. [ABSTRACT FROM AUTHOR]

Electron-impact excitation of H2 triplet states plays an important role in the heating of outer planet upper thermospheres. The state is the third ungerade triplet state, and the – emission is the largest cascade channel for the state. Accurate energies of the (v, J) levels are calculated from an ab initio potential energy curve. Radiative lifetimes of the (v, J) levels are obtained by an accurate evaluation of the – transition probabilities. The emission yields are determined from experimental lifetimes and calculated radiative lifetimes and are further verified by comparing experimental and synthetic – spectra at 20 eV impact energy. Spectral analysis revealed that multipolar components beyond the dipolar term are required to model the – excitation, and significant cascade excitation occurs at the (v = 0,1) levels. Kinetic energy (Ek) distributions of H atoms produced via predissociation of the state and the −− cascade dissociative emission are obtained. Predissociation of the state produces H atoms with an average Ek of 2.3 ± 0.4 eV/atom, while the Ek distribution of the −− channel is similar to that of the –− channel and produces H(1s) atoms with an average Ek of 1.15 ± 0.05 eV/atom. On average, each H2 excited to the state in an H2-dominated atmosphere deposits 3.3 ± 0.4 eV into the atmosphere, while each H2 directly excited to the state gives 2.2–2.3 eV to the atmosphere. The spectral distribution of the calculated – continuum emission due to the – excitation is significantly different from that of direct excitation. [ABSTRACT FROM AUTHOR]

Rotational and vibrational dependence of photodissociation cross sections and oscillator strengths to the continuum levels of the H_2{ \,}\bpxo{} and \dxo{} states have been examined. The electron-impact excitation, dissociation and emission cross sections of the \bpxi{} and \dxi{} band systems have been obtained for the first time over a wide energy range by using calculated continuum oscillator strengths along with previously published discrete transition probabilities and Lyman and Werner bands excitation functions. The present \bpxo{} photodissociation cross section from the Ji = 0 level is in excellent agreement with that obtained by Glass-Maujean (1986 Phys. Rev. A 33 346-50). Photoexcitation from the \xxo{(v_i=0)} state to the \dxo{} continuum is found to be weak. The present calculation shows significant contribution of quasi-resonance, which arises from transitions to the quasi-bound levels above the dissociation limit but stabilized by the centrifugal potential. The quasi-resonance is largely responsible for the significant rotational dependence of the continuum oscillator strength of the \bpxo{}-\xxo{(0)} transition, which, in turn, leads to the noticeable temperature dependence of electron-impact excitation and emission cross sections. \bpxi{} and \dxi{} electron-impact excitation, emission, and dissociation cross sections, important for modelling dayglow and auroral activity in the atmospheres of the outer planets, are presented. [ABSTRACT FROM AUTHOR]

Molecular tools have enabled wildlife researchers to obtain accurate information on the kinship, mating behavior, and dispersal of individuals. We genotyped 192 Ethiopian wolves (n = 29 packs) in the Bale Mountains for 17 microsatellite loci to 1) elucidate kinship within and between packs, 2) assess parentage of pups, and 3) evaluate whether inbreeding is avoided by dispersal and/or mating behavior. Mean pairwise relatedness within packs (R = 0.39) was significantly greater than that estimated from random assignment of individuals to packs. However, breeding pairs were most often unrelated, suggesting that female-biased dispersal reduces inbreeding. We assigned maternity to 49 pups and paternity to 47 pups (n = 12 litters) using a combination of exclusion, likelihood analyses (using CERVUS software), and sibship reconstruction. Multiple paternity occurred in 33% of litters; extrapack paternity accounted for 28% of all resolved paternities, occurring in 50% of litters. We found no evidence that extrapack copulations reduce inbreeding; however, more detailed analyses may elucidate the effect of recent population declines and demographic disturbances due to recurring disease outbreaks. The adaptive advantages of female-biased dispersal and the observed mating system are discussed in relation to Ethiopian wolf sociobiology and ecology. [ABSTRACT FROM AUTHOR]