Role of predators in the recruitment of invertebrates in a rocky subtidal community in the southwest Bay of Fundy,NB

ABSTRACT

Predation is potentially an in?uential source of early post-settlement mortality of benthic marine invertebrates, but previous studies demonstrate con?icting results. We investigated the effect of large predators on developing subtidal invertebrate communities in cobble-?lled collectors in the southwest Bay of Fundy, Canada. Two predation treatments (exclusion of predators ≥ 7 mm body width or full access for predators < 50 mm) were used to test the effect of large predators, and a partial-cage control tested for caging artefacts. Despite a reduction in the abundance and biomass of large predators, multivariate analyses indicated no effect of predator exclusion on the composition of the prey and micropredator communities. Results indicated that the largest differences were between the predator-access treatment and the other two treatments, which was potentially in?uenced by the caging material. There were signi?cant but weak positive correlations between the micropredator and the other two communities. Previous studies indicate that at low predation intensity, as seemed to be the case here, other factors may play a stronger role in controlling recruit abundance. Predation control probably varies spatially and temporally, and the in?uence of large predators was not likely the driving force for early post-settlement mortality in the invertebrate communities measured in this study.     

Echo 9 virus-induced order-disorder transition of chemotactic response of human polymorphonuclear leucocytes: phenomenology and molecular biology

By means of functional, morphological, and biophysical methods the in vitro interaction of Echo virus, type 9, strain A. Barty with human polymorphonuclear leucocytes (PMNs) was investigated and analyzed by statistical methods. Control cells and virus-treated PMNs (15 min, 37 degrees C; PMN: virus (pfu)-ratio ranging from 1:1 to 1:50) were exposed to a chemotactic gradient (N-formylmethionyl-leucylphenylalanine = f-Met-Leu-Phe, 10(-8) M/mm) in a Zigmond chamber. Whereas the track velocity of the moving PMNs was not affected by the virus, the degree of orientation of virus-treated PMNs declined in a way dependent on the viral dose and on the time of PMN:virus interaction, resulting in a shift from chemotactic to chemokinetic response. This virus-induced order-disorder transition of chemotactic response can be described by a logarithmic law in analogy to the Weber-Fechner law. Parallel to the functional disturbances, virus-induced changes of cell shape, which could be confirmed by additional light and electron microscopy techniques, were also detected using statistical analysis of cytological data (median cell size, anisotropy of cell shape) by means of two-dimensional histograms. To investigate f-Met-Leu-Phe- or/and Echo 9 virus-induced PMN-cell membrane changes, the monomer-excimer technique with pyrenedecanoic acid as fluorescent probe was applied, which gives information about structural changes of the cell membrane. Addition of the chemotactic peptide (10(-8) M) to control PMNs resulted in a higher rate of excimer formation obviously due to the formation of new functional (receptor) units (= activated cell membrane). Echo 9 virus exhibited an opposite effect. Quantitative analysis of these results revealed that the f-Met-Leu-Phe-induced cell membrane changes were extinguished by the addition of 2 pfu Echo 9 virus. So far, we have additional indicators of a virus-induced order-disorder transition of chemotactic response of human PMNs on a molecular biological level.     

Spatial and temporal distribution of a deposit-feeding polychaete on a heterogeneous tidal flat

The distribution of the deposit-feeding, orbiniid polychaete, Scoloplos fragilis (Verrill, 1873), was examined in relation to differences in elevation along-shore and down-shore from August 1976 to April 1977. The sand flat at Cape Henlopen, Lewes, Delaware U.S.A., is characterized by swash bars extending perpendicular to the shore, which undergo annual vertical and lateral fluctuations and have marked differences in elevations. Six stations were monitored on a single swash bar. Three sites were sampled monthly at an area on the swash bar near the beach berm (high-tide zone) and at an area near the water's edge (low-tide zone). The sites were the swash bar ridge, its depositional slope and the adjacent trough.Distribution patterns of S. fragilis were not associated with elevational gradients or a particular tidal level. Highest numbers were found on the slopes, lowest numbers on the high-tide ridge, and second lowest numbers in the low-tide trough. On the high-tide ridge, the sediments were too unstable for habitation by S. fragilis. In the low-tide trough, predation and other biological interactions apparently keep numbers of S. fragilis low. Wave and wind activity may have concentrated S. fragilis at slope stations, where sediment deposition occurs.Mean body size of S. fragilis varied spatially and temporally. Within each tidal level, mean sizes increased significantly from ridge to trough. Body sizes were significantly larger in the high-tide zone than in the low-tide zone and varied significantly with time. Reproductive maturity appears to occur after two years and at least three age-classes are present.     

Versuche über das Gehör der Noctuiden

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When humans work like beavers: riparian restoration enhances invertebrate gamma diversity and habitat heterogeneity

Restoration has the potential to increase habitat heterogeneity through the creation of unique habitat patches that, in turn, increase regional species richness or gamma diversity. While biological diversity and habitat heterogeneity are important factors to consider under a shifting climate, restoration actions and outcomes rarely examine these components. In this study, we examined the effects of riparian beaver dam analog (BDA) restoration on aquatic invertebrate diversity and habitat heterogeneity. Although the effects of BDAs on hydrology, geomorphology, and salmonid habitat have been explored, we are unaware of any studies assessing their effects on aquatic invertebrate diversity and the food web that supports them. We sampled aquatic invertebrates, basal carbon resources, dissolved nutrients, turbidity, and water temperature in pre- and post-BDA pond, side channel, and mainstem habitat over a three-year period. The BDAs functioned similarly to natural beaver dams and created slow-water environments that accumulated fine particulate organic material and increased pelagic phytoplankton production. Nonmetric multidimensional scaling, permutation multivariate analysis of variance, and Mantel's tests demonstrated that these changes led to the formation of a unique invertebrate community populated by lentic macroinvertebrates and zooplankton, which increased beta-diversity and gamma diversity. Further, BDAs in our study maintained high densities of invertebrates and buffered water temperatures in comparison to adjacent lotic habitats. These results support our hypothesis that BDAs can enhance invertebrate beta and gamma diversity through the creation and colonization of unique pond habitat and improve habitat and resource heterogeneity for native fishes under variable climate conditions.     

Dosage effect study of the microsporidian Octosporea muscaedomesticae in the adult black blowfly Phormia regina,with reference to the reproductive cycle of the pathogen

The quantitative pathogenicity of the microsporidian Octosporea muscaedomesticae in adult Phormia regina was studied. Dosage levels ranging from 10² to 10⁶ spores per fly were administered to five and six groups of newly emerged, starved adult flies in two trials. Rates of mortality and infection were determined. A direct relationship between number of spores ingested and subsequent infection rate was found in a 4-day trial while no such relationship was found in an 18-day trial, using the same source of inoculum and host flies from the same colony. The lack of a direct relationship between spore dose and rate of infection in the 18-day trial is explained on the basis of the short spore-to-spore development time of the parasite. New generations of spores formed within the host tissues obscure the results in relation to the spore dose initially administered. An appreciable number of spores in the inoculum is needed to initiate frank infection. The ID₅₀ (median infective dose) was 4.4 × 10⁴ spores per fly after 4 days.     

Saccharomyces cerevisiae-based system for studying clustered DNA damages

DNA-damaging agents can induce clustered lesions or multiply damaged sites (MDSs) on the same or opposing DNA strands. In the latter, attempts to repair MDS can generate closely opposed single-strand break intermediates that may convert non-lethal or mutagenic base damage into double-strand breaks (DSBs). We constructed a diploid S. cerevisiae yeast strain with a chromosomal context targeted by integrative DNA fragments carrying different damages to determine whether closely opposed base damages are converted to DSBs following the outcomes of the homologous recombination repair pathway. As a model of MDS, we studied clustered uracil DNA damages with a known location and a defined distance separating the lesions. The system we describe might well be extended to assessing the repair of MDSs with different compositions, and to most of the complex DNA lesions induced by physical and chemical agents.     

Zur Bewegungsphysiologie der Nemertinen. I. Emplectonema

Ohne Zusammenfassung