Commensal ecology, urban landscapes, and their influence on the genetic characteristics of city-dwelling Norway rats (Rattus norvegicus)

Movement of individuals promotes colonization of new areas, gene flow among local populations, and has implications for the spread of infectious agents and the control of pest species. Wild Norway rats ( Rattus norvegicus ) are common in highly urbanized areas but surprisingly little is known of their population structure. We sampled individuals from 11 locations within Baltimore, Maryland, to characterize the genetic structure and extent of gene flow between areas within the city. Clustering methods and a neighbour-joining tree based on pairwise genetic distances supported an east–west division in the inner city, and a third cluster comprised of historically more recent sites. Most individuals (~95%) were assigned to their area of capture, indicating strong site fidelity. Moreover, the axial dispersal distance of rats (62 m) fell within typical alley length. Several rats were assigned to areas 2–11.5 km away, indicating some, albeit infrequent, long-distance movement within the city. Although individual movement appears to be limited (30–150 m), locations up to 1.7 km are comprised of relatives. Moderate F _ST, differentiation between identified clusters, and high allelic diversity indicate that regular gene flow, either via recruitment or migration, has prevented isolation. Therefore, ecology of commensal rodents in urban areas and life-history characteristics of Norway rats likely counteract many expected effects of isolation or founder events. An understanding of levels of connectivity of rat populations inhabiting urban areas provides information about the spatial scale at which populations of rats may spread disease, invade new areas, or be eradicated from an existing area without reinvasion.     

The structure, reproduction and taxonomy of Vidalia and Osmundaria (Rhodophyta, Rhodomelaceae)

Comprises species occurring mostly in subtidal habitats in tropical, subtropical and warm-temperate areas of the world. An analysis of the type species, V. spiralis (Sonder) Lamouroux ex J. Agardh, a species from Australia, establishes basic characters for distinguishing species in the genus. These characters are (1) branching patterns of thalli, (2) flat blades that may be spiralled on their axis, (3) width of the blade, (4) primary or secondary derivation of sterile and fertile branchlets and (5) position of sterile and fertile branchlets on the thalli. Application of the latter two characters provides an important basic method for separation of species into three major groups. Osmundaria , a genus known only in southern Australia, was studied in relation to Vidalia , and its separation from the Vidalia assemblage is not accepted. Species of Vidalia therefore are transferred to the older genus name, Osmundaria. Two new species, Osmundaria papenfussii and Osmundaria oliveae are described from Natal. Confusion in the usage of the epithet, Vidalia fimbriala Brown ex Turner has been clarified, and Vidalia gregaria Falkenberg, described as an epiphyte on Osmundaria pro/ifera Lamouroux, is revealed to be young branches of the host, Osmundaria prolifera.     

Very-broad-scale assessment of human impacts on river condition

1. Management of whole rivers and river catchments requires a comprehensive set of information about river condition and use, both existing and historical, and the links between them at regional, state or national scales. This paper outlines a new approach to the assessment of river condition, using a small team was able to assess 210 000 km of rivers across more than 3 million km² of Australia in little more than a year. 2. The approach was driven by a hierarchical model of river function, which assumed that broad‐scale catchment characteristics affect local hydrology, habitat features, water quality and, ultimately, aquatic biota. The model provided the basis for selecting important ecologically relevant features that indices should represent. For each reach of each river we derived a biological index and an environmental index based on measures quantifying catchment and hydrological condition, and habitat and water quality condition. Data came from existing state and national databases, satellite images, site measurements and process models. 3. All indices were calculated as deviation from a reference condition, were range‐standardised and were divided into equivalent bands of condition. Amalgamation of index components and of sub‐indices was determined by consideration of their ecological effects; for example, general degradation might be additive, but toxic effects of one component would override all others. 4. Several internal and external validation methods were employed, with the all‐important validation of the final assessments undertaken by comparison with a similar index based on locally measured data. 5. The environmental assessment classified 14% of reaches as largely unmodified, 67% as moderately modified and 19% as substantially modified by human impacts. The biological assessment based on site assessments and modelled data using invertebrates indicated that 70% of reaches were equivalent to reference condition and that 30% were significantly impaired. Catchment disturbance, elevated sediment and nutrient loads, and habitat degradation all contributed to these results. These impacts have all occurred during the last 200 years (post‐European settlement). 6. Partly as a result of the assessments of this study the Australian Government has begun to adopt a more environmentally sustainable approach to broad‐scale water management.     

OBSERVATIONS ON THE CONTROL OF MITE INFESTATIONS IN STORED WHEAT BY CHEYLETUS SPP. (ACARINA, CHEYLETIDAE)

An account is given of the control of the grain mite Acarus siro L. (= Tyroglyphus farinae L.) by the predatory mite Cheyletus sp. in imported wheat stored in bags or in bulk. After 12–18 months of storage Cheyletus sp. had developed in 75% of the parcels of wheat and in 67% of these it became dominant over other mites. This usually occurred in late summer for bagged wheat. Control of A. siro by Cheyletus sp. compared favourably with that achieved by fumigation with methyl bromide and on occasion was superior. Both development and dominance of Cheyletus sp. were adversely affected by earlier fumigation but there was some evidence that spraying wheat with γ-BHC favoured the development of this species and, in some circumstances, its dominance. Dominance by Cheyletus sp. in bulk grain often occurred in the winter months when the surface moisture content of the wheat was at its highest.
The development of Cheyletus eruditus Schr. is described in a bulk grain store where dense populations of A. siro and Glycyphagus destructor Schr. were eliminated by the predator. The numbers of C. eruditus in wheat tended to increase faster when the surface layers were disturbed than when the grain was undisturbed. Nevertheless, dominance over the other mites tended to occur first in undisturbed grain.     

Phytotoxic Compounds produced by Fusarium equiseti

Culture filtrates of several strains of Fusarium equiseti (Corda)Sacc. were found to be highly phytotoxic. Several phytotoxicsubstances were isolated; the most important of these was acolourless crystalline compound, diacetoxyscirpenol, m.p. 161-2°,C₁₉H₂₆O₇. Though highly phytotoxic in many respects, it markedlystimulates elongation of cress roots at 0.01–0.5 µg./ml.This is not an anti-auxin effect. Diacetoxyscirpenol is at mostonly slightly inhibitory to fungi and bacteria, but is highlytoxic to rats. Two minor metabolic products, m.p. 135-6°and 185-8° respectively, are also described. They, too,were highly phytotoxic, though their spectra of activity weresomewhat different from that of diacetoxyscirpenol. They alsowere highly toxic to rats. Production of these substances isprobably not important in the aetiology of disease symptomsin plants parasitized by F. equiseti, but may be significantin cases of toxicosis of animals fed with grain infected byFusaria. Scirpentriol, a hydrolysis product of diacetoxyscirpenol,is much less phytotoxic but of equal toxicity to rats.     

Natural occurrence of deoxynivalenol, 3-acetyl-deoxynivalenol, 15-acetyl-deoxynivalenol,nivalenol, 4,7-dideoxynivalenol,and zearalenone in polish wheat

Three wheat samples collected in 1987 in Central Poland and naturally infected withFusarium spp were analyzed for the presence ofFusarium spp andFusarium toxins. Heads were separated into three fractions: kernels with visibleFusarium damage, healthy looking kernels, and chaff + rachis. The samples contained deoxynivalenol (2.0 – 40.0μg/g), nivalenol (O.O1μg/g), 4,7-dideoxynivalenol (0.10 – 0.15μg/g). 15-acetyldeoxynivalenol (0.10–2.00 μg/g), 3-acetyldeoxynivalenol (O/1Oμg/g), and zearalenone (0.01–2.00μg/g). This is the first report about 15 - acetyldeoxynivalenol in European wheat and the co-occurrence of 3 - acetyldeoxynivalenol and 15-acetyldeoxynivalenol in the same sample of contaminated cereals.