Development, structure and function of rhinoceros enamel

Vertical enamel prism decussation in the inner-layer enamel of rhinoceroses occurs as the result of vertical translation, in opposite senses, of zones of ameloblasts, which begins very shortly after amelogenesis commences at the enamel-dentine junction. Prisms in the centre of the decussating zones are stacked in the Pattern 3 arrangement. Zone boundary prisms adopt intermediate orientations, are locally nearly perpendicular to the enamel surface, and have a cylindrical, Pattern 1 cross-section. Decussation also continues in the outer-layer enamel, but the prisms all have occlusal-going courses: the occlusal-going zones of the inner enamel continue as the more occlusally oriented zones of the outer layer. Abrasion resistance to diamond polishing and soft abrasive projectile erosion (air-polishing with NaHCOs) and resistance to ion beam erosion is greater with distance from the nearest prism boundary discontinuity. Polished surface areas containing longitudinally sectioned prisms are more prone to 'air-polishing' and 'airbrading' erosion than areas with transversely sectioned prisms. These observed relationships fully explain the relief developed at natural wear surfaces.     

A Method for the Isolation of Stable Mesophyll Protoplasts from Tomato Leaves throughout the Year under Standard Conditions

A method is described, based on growing tomato plants under low light intensities and feeding with calcium nitrate, whereby stable protoplasts can be isolated throughout the year under standard conditions. Plants are grown in the equivalent of spring and winter light intensities (i. e. incoming solar radiation 2.52 to 10.8 MJ m^?2 day^?1 15 h day) in the glasshouse on peat compost supplied with a balanced fertilizer containing nitrate and urea as nitrogen sources and given a supplementary feed of calcium nitrate. Under these conditions, high yields of protoplasts can be isolated on incubation in the dark using low enzyme concentrations at 25°C for 2 h. Protoplasts isolated in this way can support tobacco mosaic virus replication and are capable of cell division.     

What limits a rare alpine plant species? Comparative demography of three endemic species of Myosotis (Boraginaceae)

Abstract Establishing what are the underlying causes of species range limits is of fundamental interest in ecology. We followed the fate of individually mapped plants of three endemic New Zealand high‐alpine species of Myosotis, over a period of 9 years. The species provide contrasts in their geographical range and their demography. Myosotis oreophila Petrie is rare and extremely localized (c. 0.5 ha extent), Myosotis cheesemanii Petrie is regionally endemic, and Myosotis pulvinaris Hook. f. is more widespread. All three occur on the Dunstan Mountains, Central Otago, South Island, New Zealand within a 1‐km radius, and individual plants were followed in four permanent plots. The three species differed in their longevity and in population variability, with the most widespread species (M. pulvinaris) having the lowest survival (61% per year), the fewest old plants (only 3% of plants present in 1993 surviving until 2001), no increase in survival rates with age, and the most variability in total numbers across years. Both of the rare species, M. oreophila and M. cheesemanii, had higher survival (75% and 88%, respectively, per year) especially for older plants, many older plants (20% and 59%, respectively, of 1993 plants surviving until 2001), and lower variability in total numbers across years. These results are consistent with other studies showing that rare plant species tend to have higher inertia than more common congeners. The range limits of M. oreophila showed a high level of spatial constancy on a scale of metres over the 9 years, despite 80% turnover in plants during that time. The M. oreophila population showed lower mean densities of plants near to the population boundaries, identical age‐specific survival rates, but lower flowering probabilities, than the core of the population. We were unable to detect any abiotic differences between inside and outside the M. oreophila range in terms of topography, soil parent materials, microclimate or through manipulation of snow cover. Disturbance may be a factor affecting the distribution of M. cheesemanii but limiting factors for M. oreophila and M. pulvinaris are likely to be biotic (competition, seed limitation, dispersal capacity) and/or historic. Further experimentation is recommended.     

Influence of Anthropogenic Structures on Northern Bobwhite Space Use in Western Oklahoma

ABSTRACT Anthropogenic structures associated with energy development and other activities are a growing concern in wildlife conservation because of habitat loss and fragmentation. We conducted a retrospective analysis of effects of barbed-wire fences, oil-extraction structures, aboveground power lines, resurfaced roads, and artificial water sites on space use by northern bobwhite (Colinus virginianus)in western Oklahoma, USA. Nest location data accrued during 1991–2002 and radiolocation data during 1997–2002. Data suggested fences had a weak repellent effect at distances <300 m, oil structures had neutral effects at distances <800 m, aboveground power lines had neutral effects at distances <250 m, resurfaced roads attracted at distances <350 m, and water sites had neutral effects at distances <250 m. Generally, anthropogenic structures seemed compatible with bobwhite populations on our study area, given density and dispersion of the structures that existed.     

Phylogeography of lions (Panthera leo ssp.) reveals three distinct taxa and a late Pleistocene reduction in genetic diversity

Lions were the most widespread carnivores in the late Pleistocene, ranging from southern Africa to the southern USA, but little is known about the evolutionary relationships among these Pleistocene populations or the dynamics that led to their extinction. Using ancient DNA techniques, we obtained mitochondrial sequences from 52 individuals sampled across the present and former range of lions. Phylogenetic analysis revealed three distinct clusters: (i) modern lions, Panthera leo ; (ii) extinct Pleistocene cave lions, which formed a homogeneous population extending from Europe across Beringia (Siberia, Alaska and western Canada); and (iii) extinct American lions, which formed a separate population south of the Pleistocene ice sheets. The American lion appears to have become genetically isolated around 340 000 years ago, despite the apparent lack of significant barriers to gene flow with Beringian populations through much of the late Pleistocene. We found potential evidence of a severe population bottleneck in the cave lion during the previous interstadial, sometime after 48 000 years, adding to evidence from bison, mammoths, horses and brown bears that megafaunal populations underwent major genetic alterations throughout the last interstadial, potentially presaging the processes involved in the subsequent end-Pleistocene mass extinctions.     

Long‐term variation in the littoral food web of an acidified mountain lake

Evidence of chemical recovery from acidification in European freshwaters has emerged in recent years, with many previously damaged systems responding to decades of reduced acidifying emissions. Biological recovery, however, has often lagged behind, and this has been ascribed to several possible mechanisms, including inertia in the food web. We examined two decades of change in hindcasted food webs for Lochnagar, a Scottish mountain lake, to make inferences about the potential dynamical stability of the system and to assess the prospects for future biological recovery. Although community composition tracked temporal changes in acidity, this was neither sustained nor directional, and mainly manifested as shifts in relative abundances rather than the establishment of more acid‐sensitive species. The food web was highly interconnected and reticulate, especially in years when species richness was low, and subsidized by external inputs of detritus. Among the primary consumers, generalist herbivore–detritivores maintained feeding links with the scant algal resources, which appeared insufficient to support viable populations of specialist grazers. Together, these characteristics, which are shared with many other acidified freshwaters, are likely to make the community dynamically stable and resistant to invasions of potential new colonists, thereby slowing the pace of future biological recovery.     

Ten informative markers developed from WRKY sequences in coconut (Cocos nucifera)

Coconut (Cocos nucifera L.) WRKY sequences containing single nucleotide polymorphisms (SNPs) and one microsatellite repeat were used to develop 10 informative markers. These markers were evaluated in 15 genotypes representing six coconut cultivars. SNP‐containing alleles were detected by single‐strand conformation polymorphism (SSCP) analysis. The number of detected alleles ranged from two to four. Five pairs of loci were in linkage disequilibrium in the test population. These markers are currently being evaluated in more individuals/cultivars to determine their value in estimating the genetic diversity of this species.