Population genetic structure of savannah elephants in Kenya: conservation and management implications

We investigated population genetic structure and regional differentiation among African savannah elephants in Kenya using mitochondrial and microsatellite markers. We observed mitochondrial DNA (mtDNA) nucleotide diversity of 1.68% and microsatellite variation in terms of average number of alleles, expected and observed heterozygosities in the total study population of 10.20, 0.75, and 0.69, respectively. Hierarchical analysis of molecular variance of mtDNA variation revealed significant differentiation among the 3 geographical regions studied (F(CT) = 0.264; P < 0.05) and a relatively lower differentiation among populations within regions (F(SC) = 0.218; P < 0.0001). Microsatellite variation significantly differentiated among populations within regions (F(SC) = 0.019; P < 0.0001) but not at the regional levels (F(CT) = 0.000; P > 0.500). We attribute the high differentiation at the mitochondrial genome to the matrilineal social structure of elephant populations, female natal philopatry, and probably ancient vicariance. Lack of significant regional differentiation at the nuclear loci vis-a-vis strong differences at mtDNA loci between regions is likely the effect of subsequent homogenization through male-mediated gene flow. Our results depicting 3 broad regional mtDNA groups and the observed population genetic differentiation as well as connectivity patterns should be incorporated in the planning of future management activities such as translocations.     

The effect of a single application of cow urine on annual N2 fixation under varying simulated grazing intensity, as measured by four 15N isotope techniques

The effects of dairy cow urine and defoliation severity on biological nitrogen fixation and pasture production of a mixed ryegrass-white clover sward were investigated over 12 months using mowing for defoliation. A single application of urine (equivalent to 746 kg N ha^–1), was applied in late spring to plots immediately after light and moderately-severe defoliation (35 mm and 85 mm cutting heights, respectively) treatments were imposed. Estimates of percentage clover N derived from N₂ fixation (%Ndfa) were compared by labelling the soil with ¹⁵N either by applying a low rate of ¹⁵N-labelled ammonium sulphate, immobilising ¹⁵N in soil organic matter, adding ¹⁵N to applied urine, or by utilising the small differences in natural abundance of ¹⁵N in soil. Urine application increased annual grass production by 85%, but had little effect on annual clover production. However, urine caused a marked decline in %Ndfa (using an average of all ¹⁵N methods) from 84% to a low of 22% by 108 days, with recovery to control levels taking almost a year. As a result, total N fixed (in above ground clover herbage) was reduced from 232 to 145 kg N ha^–1 yr^–1. Moderately–severe defoliation had no immediate effect on N₂ fixation, but after 108 days the %Ndfa was consistently higher than light defoliation during summer and autumn, and increased by up to 18%, coinciding with an increase in growth of weeds and summer-grass species. Annual N₂ fixation was 218 kg N ha^–1 yr^–1 under moderately-severe defoliation compared to 160 kg N ha^–1 yr^–1 under light defoliation. Estimates of %Ndfa were generally similar when ¹⁵N-labelled or immobilised ¹⁵N were used to label soil regardless of urine and defoliation severity. The natural abundance technique gave highly variable estimates of %Ndfa (–56 to 24%) during the first 23 days after urine application but, thereafter, estimates of %Ndfa were similar to those using ¹⁵N-labelling methods. In contrast, in urine treated plots the use of ¹⁵N-labelled urine gave estimates of %Ndfa that were 20–30% below values calculated using conventional ¹⁵N-labelling during the first 161 days. These differences were probably due to differences in the rooting depth between ryegrass and white clover in conjunction with treatment differences in ¹⁵N distribution with depth. This study shows that urine has a prolonged effect on reducing N₂ fixation in pasture. In addition, defoliation severity is a potential pasture management tool for strategically enhancing N₂ fixation.     

Rhizobium specific anthocyanin-like marker in lupin nodules

Summary A Rhizobium specific anthocyanin-like pigment has been isolated from nodules ofLupinus arboreus. The pigment is located in the nodule cortex. Comparison of normal nodules and nodules containing this red pigment showed that the latter had a lower proportion of bacteroid tissue and a lower nitrogenase activity.Anisolate of this type is designated PDD4142 and is lodged with Plant Diseases Division, DSIR, P.B., Auckland, New Zealand.     

A Quantitative Estimation of the Uptake of Two New Electron Stains by the Cytoplasmic Membrane of Ram Sperm

From microdensitometer measurements on electron micrographs of sectioned sperm heads it has been found that the electron stains, triiodobenzoyl chloride, and triiodophenylisocyanate, increase the image contrast of the cell membrane above its immediate background by about 40 per cent and 70 per cent respectively, while the nucleus remains unstained. Assumptions based on current electron scattering theory have been used to deduce the uptake by weight of the stains in terms of the density of the nucleus, which was estimated from complementary measurements made with the interference microscope and electron microscope. The uptake of the stains was found to be about 7 per cent and 12 per cent by weight respectively. It is suggested that the method used in this work could be applied generally for the density measurement of cell structures unresolved by the light microscope.     

Frankia vesicles provide inducible and absolute oxygen protection for nitrogenase

When Frankia HFPCcI3 was grown in culture at oxygen O₂ levels ranging from 2 to 70 kilopascals O₂, under nitrogen fixing conditions, nitrogenase activity adapted to ambient pO₂ and showed a marked optimum close to growth pO₂. Vesicles were thin walled at low pO₂ and very thick walled at high pO₂. Freeze fracture transmission electron microscopy confirmed that Frankia produces vesicles with outer walls thickened by multiple lipid-like monolayers, in proportion to ambient pO₂.