THE ABSORPTION, BREAKDOWN AND SYSTEMIC BEHAVIOUR IN PLANTS OF 32P-LABELLED DEMETON-S

Investigations are described on the general behaviour of diethyl-5-(a-ethylthioethyl) phosphorothiolate (demeton-S) labelled with ³²P, after leaf application to beans, apples and Coleus ; and to the roots of beans growing in soil or sand.
Following leaf application, three processes, evaporation, breakdown into toxic non-volatile compounds, and absorption, occurred concurrently and effectively removed unchanged demeton-S from the leaf surface within a few hours. The evaporation gave rise to a fumigant action on Aphis fubue. Both demeton-S and its degradation products were absorbed, the former degrading rapidly within the tissue untreated foliage. In no instance following leaf application could any unchanged demeton-S be found elsewhere in the plant. Analyses showed a higher proportion of primary toxic degradation products in the treated than in the untreated leaves.
Translocation from treated leaves was never sufficient to kill aphids feeding on the Following root application to beans in soil or sand, aphids feeding on the shoot tips were killed after z days; unchanged demeton-S was translocated following root application.
Demeton-S and its toxic derivatives appeared to move much more freely in xylem than in phloem tissue; movement from xylem to phloem must occur, but subsequent transport within the latter tissue is limited.
Autoradiographic evidence confirmed the limited extent of movement within leaves.     

Recolonization of forest fragments by a native rodent following experimental ‘extinctions’

The movement of organisms between subdivided populations is considered a key influence on the persistence of species in modified landscapes. In particular, the ability to recolonize ‘empty’ fragments of habitat is directly relevant to conservation management, and to understanding the link between pattern and process in metapopulations. We studied the movement and recolonization ability of the bush rat, Rattus fuscipes, in a highly fragmented agricultural landscape in south‐western Victoria, Australia. Populations were monitored in seven small (<2.5 ha) and two large (>49 ha) forest fragments before removal of all residents from four of the small fragments. Subsequent monitoring (for up to 16 months) allowed the detection of colonizing individuals, and comparisons between ‘experimental’ and ‘control’ fragments. Rattus fuscipes readily moved between fragments and successfully recolonized (i.e. both males and females arrived) two of four fragments in which extinctions were simulated. A single male moved into a third experimental fragment. In one fragment, new animals were detected 1 month after the removal of residents, indicating that recolonization can occur rapidly. Dispersers were not a random sample of the population: although both males and females, and adults and sub‐adults were recorded dispersing, adult males in reproductive condition predominated. Functional connectivity appears to be high for R. fuscipes in the study landscape. Results from this manipulative experiment provide direct empirical evidence that a capacity for movement allows recolonization of fragments of suitable habitat and is a key process responsible for species persistence in fragmented landscapes, as predicted by theory.     

The Osteology of Infants and Children

The Osteology of Infants and Children . Brenda J. Baker, Tosha L. Dupras, and Matthew W. Tocheri. College Station: Texas A&M University Press, 2005. 178 pp.     

Speciation mirrors geomorphology and palaeoclimatic history in African laminate-toothed rats (Muridae: Otomyini) of the Otomys denti and Otomys lacustris species-complexes in the 'Montane Circle' of East Africa

We adopted an integrated systematic approach to delimit evolutionary species and describe phylogeographic, morphometric and ecological relationships in Otomys denti (from the Albertine Rift, Southern Rift in Malawi and the northern Eastern Arc Mountains) and Otomys lacustris (from the Southern Rift in Tanzania and Zambia, and the southern Eastern Arc Mountains). Molecular [cytochrome (cyt) b sequences, 1143 bp, N  = 18], craniometric (classical, N  = 100 and geometric, N  = 60) and ecological (Partial Least Squares regression of shape and ecogeographic variables) approaches show a profound, parallel disjunction between two groups: (1) Eastern Arc and Southern Rift (including the Malawi Rift) ( O. lacustris and Otomys denti sungae ) and (2) Albertine Rift ( Otomys denti denti and Otomys denti kempi ) taxa. Within both groups, cyt b sequences or craniometric analysis provided evidence for the differentiation of both southern and northern Eastern Arc from Southern Rift lineages (across the so-called Makambako Gap). Within the Albertine Rift ( denti – kempi ) lineage, populations from individual mountain ranges differed significantly in skull shape (but not size), but were similar genetically. Over-reliance in the past on very few morphological characters (e.g. number of molar laminae) and a polytypic species concept has obscured phylogenetic relationships and species discrimination in this group. We recognize at least three species in this group, and distinct lineages within two of these species. Each species or lineage was endemic to one of three regions: the Albertine Rift, the Malawi Rift or the Eastern Arc. Our result echo conclusions of recent studies of other mammalian and bird taxa and reflect the geomorphology and palaeoclimatic history of the region.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 913–941.     

Perspectives on polyploidy in plants – ancient and neo

It is timely to re-examine the phenomenon of polyploidy in plants. Indeed, the power of modern molecular technology to provide new insights, and the impetus of genomics, make polyploidy a fit, fashionable and futuristic topic for review. Some historical perspective is essential to understand the meaning of the terms, to recognize what is already known and what is dogma, and to frame incisive questions for future research. Polyploidy is important because life on earth is predominantly a polyploid phenomenon. Moreover, civilization is mainly powered by polyploid food – notably cereal endosperm. Ongoing uncertainty about the origin of triploid endosperm epitomizes our ignorance about somatic polyploidy. New molecular information makes it timely to reconsider how to identity polyploids and what is a polyploid state. A functional definition in terms of a minimal genome may be helpful. Genes are known that can raise or lower ploidy level. Molecular studies can test if, contrary to dogma, the relationship between diploids and polyploids is a dynamic two-way system. We still need to understand the mechanisms and roles of key genes controlling ploidy level and disomic inheritance. New evidence for genome duplications should be compared with old ideas about cryptopolyploidy, and new views of meiosis should not ignore premeiotic genome separation. In practice, new knowledge about polyploidy will be most useful only when it reliably predicts which crops can be usefully improved as stable autopolyploids and which genomes combined to create successful new allopolyloids.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 411–423.     

Foraging strategies and patch distributions: intraguild interactions between Dicyphus hesperus and Encarsia formosa

Abstract 1. Competing foragers are affected by the distribution of resources, but can also affect resource distribution. Intraguild predators may affect the distribution of both the shared prey and the intraguild prey, which are also their competitors. 2. Variation in foraging strategies and their effects on resource distributions may influence the outcome of intraguild interactions between an intraguild predator and its intraguild prey. This was tested using whitefly Trialeurodes vaporariorum as the shared resource, the parasitoid Encarsia formosa as the intraguild prey, and Dicyphus hesperus, an omnivore, as the intraguild predator on tomato (Lycopersicon esculentum) and mullein (Verbascum thapsus) plants, within enclosures in a greenhouse. Treatments were established with and without the intraguild predator and at high and low intraguild prey densities. 3. The interaction between D. hesperus and E. formosa showed significant asymmetry, with D. hesperus populations being unaffected by E. formosa densities, although E. formosa populations were reduced by the inclusion of D. hesperus. However, the inclusion of D. hesperus diminished density‐dependent effects limiting E. formosa populations at high release densities. 4. Dicyphus hesperus reduced the average patch size and the proportion of patches occupied by whitefly. Increasing the release rate of E. formosa had no effect on any distributional measure. Based upon the foraging ecology of both species, the foraging activities of D. hesperus appear to have modified the patch distribution so that its foraging strategy becomes more successful than that of E. formosa. These properties may provide an important mechanism determining the outcome of species interactions.