Growth and Development of the Banana Plant Gross Leaf Emergence

The banana leaf must pass through a prolonged growth periodwhile totally within the pseudostem and with the lamina in aninvolved double coil. During this time the blade makes mostof its growth, completing the last fourth of the expansion asit emerges. In this same latter period it accomplishes almosttwo-thirds of its elongating growth. The first few leaves of a single plant are essentially bladeless.Thereafter the size of the lamina increases in both dimensionswith each succeeding leaf tending to exceed its predecessor.A diurnal/nocturnal cycle is evident in both Costa Rica andHonduras and maximal elongation coincides with the highest temperaturein the daylight hours. Control of elongation is elegant witheach leaf developing at a rate governed by those ahead of it.An assessment is made of the stomatal occurrence over the surfaceof the blade.     

Evolution of micromorphological and chemical characters in the lichen-forming fungal family Pertusariaceae

Micromorphological characters of the fruiting bodies, such as ascus-type and hymenial amyloidity, and secondary chemistry have been widely employed as key characters in Ascomycota classification. However, the evolution of these characters has yet not been studied using molecular phylogenies. We have used a combined Bayesian and maximum likelihood based approach to trace character evolution on a tree inferred from a combined analysis of nuclear and mitochondrial ribosomal DNA sequences. The maximum likelihood aspect overcomes simplifications inherent in maximum parsimony methods, whereas the Markov chain Monte Carlo aspect renders results independent of any particular phylogenetic tree. The results indicate that the evolution of the two chemical characters is quite different, being stable once developed for the medullary lecanoric acid, whereas the cortical chlorinated xanthones appear to have been lost several times. The current ascus-types and the amyloidity of the hymenial gel in Pertusariaceae appear to have been developed within the family. The basal ascus-type of pertusarialean fungi remains unknown.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 615–626.     

Heavily exploited but poorly known: systematics and biogeography of commercially harvested pythons (Python curtus group) in Southeast Asia

More than 100000 blood pythons (brongersmai) and short-tailed pythons (curtus and breitensteini) are taken from Borneo and Sumatra each year for the commercial leather trade. Traditionally, all have been treated as a single polytypic species (Python curtus) , with three subspecies differing in colour, size and geographic distribution. Analyses of DNA sequences and morphological data clarify the phylogenetic relationships, taxonomy and biogeography of this group. The lineage is monophyletic, and each of the three subspecies differs from the other two both morphologically and genetically. Given the morphological and genetic distinctiveness of each taxon, we here elevate the three subspecies to full species status. Python brongersmai is the most distinctive in terms of colour (of the three, only brongersmai has colour-morphs that are red or orange), size (it grows to 2.6 m, vs. approx. 2.0 m for the other taxa), and scalation (e.g. brongersmai has <166 ventral scales, vs. <166 in the other taxa and has two supralabials over each orbit, vs. one supralabial for the other two taxa). In terms of cytochrome b mitochondrial DNA sequence data, brongersmai is almost as distant genetically from the short-tailed pythons (8.9% divergence) as is the reticulated python (P. reticulatus: 10.3% divergence). The other two taxa (P. breitensteini from Kalimantan and P. curtus from western and southern Sumatra) are closely related (3% divergence), despite their disjunct distribution (separated by P. brongersmai). Sea-level fluctuations provide a plausible biogeographic scenario to explain phylogenetic divergence within this lineage. Given the distinctiveness of the component taxa, and the ease with which even dried skins can be identified to species level (based on ventral counts), the managers of this important commercial resource should no longer treat the P. curtus group as a single biological taxon.     

Evidence of drought-induced stress on biotic crust moss in the Mojave Desert

Widespread bleaching (chlorosis) of patches of the dominant desert moss Syntrichia caninervis was observed across the northern Mojave Desert in the winter of 2002–03 following an extended period of drought interrupted by small rain events. These rain events were more frequent during the warmer months just prior to the appearance of chlorosis. We hypothesized that the patches were experiencing physiological stress due to partial hydration/rapid dehydration cycling during the warmer months. Compared to unbleached (green) shoots, chlorotic shoots exhibited significantly reduced photochemical performance, photosynthetic pigments, regenerational potential, sex expression, and lower rates of growth and productivity. However, age-specific analyses revealed older leaves from chlorotic shoots did not show the typical decline in vigour, suggesting that stress may primarily affect younger tissues. It is concluded that this chlorosis phenomenon is indicative of physiological stress presently occurring in the Mojave Desert, and is likely due to exposure to a higher than normal frequency of light rain events (< 3.5 mm), which serve to partially hydrate moss patches that then rapidly desiccate .     

Estimation of migration from a perturbation experiment in natural populations of Drosophila buzzatii Patterson & Wheeler

In order to estimate migration and gene flow, allele frequencies in populations at two sites separated by 120 m were differentially perturbed by the continuous release over 413 days of flies homozygous at particular allozyme loci. The effects of perturbation were determined by genotype assay at two collections prior to, thirteen during and nine after the perturbation period. Maximum likelihood methods were developed to estimate migration into the two populations from the homozygous releases, and migration between the two populations. The successful perturbation of allele frequencies in a natural population is demonstrated. A plateau in allele frequencies during perturbation and a return to original frequencies following cessation of perturbation was most likely due to selection during development against recessive alleles concurrently introduced into the populations by the released flies. There is unequivocal evidence for short distance gene flow between the two populations. The migration rates estimated at ten times over a nine month period were extremely variable, but with higher population density at one site positively related with migration from that site to the other.     

Changing nutrient levels in Grasmere, English Lake District, during recent centuries

1. Historical nutrient changes in Grasmere were investigated using a 300‐year record derived from six sediment cores. One core was investigated at high resolution for diatoms, total sedimentary phosphorus, and loss‐on‐ignition (LOI), and was dated using ²¹⁰Pb and ¹³⁷Cs. Six other cores were scanned for magnetic susceptibility, diatoms and LOI to confirm the stratigraphic integrity of the primary record. 2. A rise in nutrient levels occurred after 1855 AD. This event was marked by a shift away from benthic diatom assemblages and a rise in Asterionella formosa. The onset of eutrophication from 1855 corresponds to the expansion of the local and tourist population in the area. 3. The replacement of A. formosa with Cyclotella spp. ca 1945–65 indicates reduced nutrient loads, possibly because of enhanced flushing brought about by the seasonal rainfall distribution. 4. After 1965 a step‐wise increase in both absolute and relative amounts of Asterionella was found. High sedimentary P and diatom inferred TP confirmed the high nutrient loading of the lake. Nutrient increase is attributable to problems with the Grasmere village sewage system and the installation of a wastewater treatment works (WwTW) on the River Rothay in 1971. Modifications to the WwTW in 1982 caused an initial improvement, but have not led to a full recovery to pre‐1965 ecological conditions. 5. The diatom record indicates a further improvement after 1990 by a return toward Achnanthes minutissima. 6. The sedimentary archive of sensitive sites provides important benchmarks against which to judge the attainment of water quality targets.     

Studies in the Respiratory and Carbohydrate Metabolism of Plant Tissues2

Feeding strawberry and poplar leaves with iodoacetate, arsenite,or fluoride decreased the contents of sucrose and ascorbate.The content of hexose increased in high concentrations of iodoacetatebut decreased in moderate strengths. Iodo-acetate increasedthe rate of CO₂ output and caused a large decrease in phospholipidwith increase of inorganic phosphate. When iodoacetate was fedin nitrogen, CO₂ output did not increase. An explanation of the results is that the sucrose and ascorbateof the cell are mainly confined to the vacuole and that theabove poisons accelerate the leakage of these compounds fromthe vacuole so that they are metabolized more rapidly in thecytoplasm. An additional possibility is that iodoacetate ‘uncouples’oxidative phosphorylation, thereby stimulating respiration andmore rapid metabolism of both sucrose and ascorbate.