An experimental investigation of enhanced harpacticoid (Copepoda) abundances around isolated seagrass shoots

Summary Premature leaf abscission in Populus was observed in central Washington (USA) about two weeks after the 18 May 1980 ashfall from Mount St. Helens. Leaf abscission was probably a wounding response caused by sandsized ash carried in winds that gusted to 15 m s^-1 7 days after the ashfall. Under glasshouse conditions simulating this environmental regime the leaf epidermis and often part of the mesophyll in Populus nigra L. var. italica Duroi. were abraded, resulting in permanent loss of leaf turgor and decreased stomatal conductance. Substantial abscission of still-green leaves ensued. Leaf abrasion by ash-laden winds, although rare, may result in conspicuous plant damage.     

Direct and indirect responses of a freshwater food web to a potent synthetic oestrogen

Endocrine-disrupting chemicals (EDCs) in municipal effluents directly affect the sexual development and reproductive success of fishes, but indirect effects on invertebrate prey or fish predators through reduced predation or prey availability, respectively, are unknown. At the Experimental Lakes Area in northwestern Ontario, Canada, a long-term, whole-lake experiment was conducted using a before-after-control-impact design to determine both direct and indirect effects of the synthetic oestrogen used in the birth control pill, 17α-ethynyloestradiol (EE2). Algal, microbial, zooplankton and benthic invertebrate communities showed no declines in abundance during three summers of EE2 additions (5–6 ng l⁻¹), indicating no direct toxic effects. Recruitment of fathead minnow (Pimephales promelas) failed, leading to a near-extirpation of this species both 2 years during (young-of-year, YOY) and 2 years following (adults and YOY) EE2 additions. Body condition of male lake trout (Salvelinus namaycush) and male and female white sucker (Catostomus commersonii) declined before changes in prey abundance, suggesting direct effects of EE2 on this endpoint. Evidence of indirect effects of EE2 was also observed. Increases in zooplankton, Chaoborus, and emerging insects were observed after 2 or 3 years of EE2 additions, strongly suggesting indirect effects mediated through the reduced abundance of several small-bodied fishes. Biomass of top predator lake trout declined by 23–42% during and after EE2 additions, most probably an indirect effect from the loss of its prey species, the fathead minnow and slimy sculpin (Cottus cognatus). Our results demonstrate that small-scale studies focusing solely on direct effects are likely to underestimate the true environmental impacts of oestrogens in municipal wastewaters and provide further evidence of the value of whole-ecosystem experiments for understanding indirect effects of EDCs and other aquatic stressors.     

Visual computation and saccadic eye movements: a theoretical perspective

A simple instance of parallel computation in neural networks occurs when the eye orients to a novel visual target. Consideration of target-elicited saccadic eye movements opens the question of how spatial position is represented in the visual pathways involved in this response. It is argued that a point-for-point retinotopic coding of spatial position (the 'local sign' approach) is inadequate to account for the characteristics of the response. An alternative approach based on distributed coding is developed.     

Seasonal Variation in the Structure of a Marine Benthic Microbial Community

Abstract The patterns of seasonal variation in the structure of a marine benthic microbial community were examined using phospholipid fatty acid analysis (PLFA). Principal component analysis of PLFA profiles indicated a strong seasonal pattern dominated the variance within the data set. Three functional groups of microorganisms (phototrophic microeukaryotes, and two groups of anaerobic bacteria) were disproportionately abundant in the communities that mapped to either extreme of the first principle component. Phototrophic microeukaryotes were most abundant and exhibited the greatest relative abundance during periods of cold water. In contrast, the two functional groups of anaerobic bacteria showed the greatest relative abundance during times of warm water. Differential responses by these groups, and macrofaunal deposit feeders, to light intensity and water temperature were offered as the proximal causes of the observed patterns. Received: 28 April 1997; Accepted: 10 September 1997     

SURVIVAL OF AN UNIRRADIATED SALMONELLA TYPHIMURIUM MARKER STRAIN INOCULATED IN POULTRY FEEDS AFTER IRRADIATION

The present study was designed to compare unirradiated Salmonella typhimurium survival during storage after inoculation in either irradiated or unirradiated poultry feed. The effects of irradiation (5 kGy) on the indigenous feed microflora and on the survival of marker strain of S. typhimurium contaminated after irradiation treatment were determined during 56 days of storage of either soybean meal (SBM) or meat and bone meal (MBM) based feeds. The initial aerobic bacterial populations were reduced more than 90% in both SBM (4.96 to 4.08 ± 0.03 log₁₀ CPU/g feed) and MBM (5.12 to 3.90 ± 0.03) by irradiation. Irradiation treatment reduced the average fungal counts during 56 days of storage in both SBM (4.24 to 2.74 ± 0.03) and MBM (4.38 to 2.15 ± 0.03) containing feeds. However, unirradiated S. typhimurium populations inoculated after irradiation of the feed were not different in either irradiated or nonirradiated SBM and MBM based feeds. Therefore, the differences in fungal versus bacterial sensitivity among the feed types and storage times suggests that gamma irradiation can alter the makeup of indigenous microbial populations in feed but this does not appear to have a discernible influence on subsequent survival of unirradiated S. typhimurium added as a dry inoculum after irradiation.     

Reproductive patterns of selected understorey trees in the Malaysian rain forest: the sexual species

HA, C. O., SANDS, V. E., SOEPADMO, E. & JONG, K., 1988. Reproductive patterns of selected understorey trees in the Malaysian rain forest: the sexual species. Investigations were carried out on the floral, fruit and seed biology, and the embryology of representatives of the Sapindaceae and Bombacaceae which occur in the lower canopy of the lowland rain forest of Peninsular Malaysia. Pollination studies indicated cross-compatibility and outbreeding in all species examined, associated with self-compatibility in the polygamous monecious Pometia pinnata and Allophylus cobbe and, to a limited extent, in the effectively dioecious Xerospermum intermedium . In these sapindaceous species, together with the self-incompatible androdioecious Nephelium lappaceum , the structurally hermaphrodite flowers were determined embryologically to be functionally female with no anther dehiscence. The self-incompatible Durio griffithii of the Bombacaceae, and X. intermedium, N. lappaceum and P. pinnata were shown by embryological studies to form a sexual zygote. The observations on these outcrossing species are considered in relation to their potential for gene exchange and their contribution to the maintenance of species diversity in the lowland rain forest.     

A novel sterol peroxide from the sea anenome Metridium senile

Nine 5 alpha, 8 alpha-epidioxy delta 6 and delta 6,9(11) sterols were identified including the hitherto unknown (22E)-5,8-epidioxy-5 alpha, 8 alpha-stigmasta-6,9(11),22-trien-3 beta-ol 9 from the sea anenome Metridium senile based on 200 MHz 1Hnmr and mass spectral data.