MD-2 binds to bacterial lipopolysaccharide

The exact roles and abilities of the individual components of the lipopolysaccharide (LPS) receptor complex of proteins remain unclear. MD-2 is a molecule found in association with toll-like receptor 4. We produced recombinant human MD-2 to explore its LPS binding ability and role in the LPS receptor complex. MD-2 binds to highly purified rough LPS derived from Salmonella minnesota and Escherichia coli in five different assays; one assay yielded an apparent KD of 65 nm. MD-2 binding to LPS did not require LPS-binding proteins LBP and CD14; in fact LBP competed with MD-2 for LPS. MD-2 enhanced the biological activity of LPS in toll-like receptor 4-transfected Chinese hamster ovary cells but inhibited LPS activation of U373 astrocytoma cells and of monocytes in human whole blood. These data indicate that MD-2 is a genuine LPS-binding protein and strongly suggest that MD-2 could play a role in regulation of cellular activation by LPS depending on its local availability.     

Lack of Dosage Compensation for an Autosomal Gene Relocated to the X Chromosome in DROSOPHILA MELANOGASTER

Aldehyde oxidase activity has been measured in flies with the structural gene for this enzyme translocated to the X chromosome. These measurements are presented as experimental evidence that, in Drosophila melanogaster, an autosomal gene relocated to the X chromosome is not dosage compensated.     

A Comparison of Sampling Techniques for Quantifying Abundance of the Florida Apple Snail (Pomacea Paludosa Say)

Despite the long recognized importance of apple snails (Pomaceapaludosa Say) in Florida wetland food webs, surprisingly littleis known about their life history and ecology. The paucity ofinformation is due, in part, to the lack of a validated samplingtechnique. In this study, we compared the effectiveness of adip net, bar seine, and suction dredge in extracting apple snailsfrom 1-m² throw traps. We also evaluated the reliability ofegg cluster counts as an index of snail abundance. The bar seine was eliminated as a suitable extraction methodbased on poor performance in densely vegetated habitats. Thesuction dredge appeared slightly less sensitive than the dipnet to habitat differences with regards to both marked snailrecovery and higher yield of free-ranging (unmarked, not previouslyextracted) snails. Our results indicate that the probabilityof recovering snails from throw traps can be considerably lessthan 1.0, and that recovery probabilities vary among sites andhabitats. Therefore, without reliable estimates for the fraction ofanimals recovered, density estimates, especially comparisonsamong sites and habitats, are not reliable. We found no relationship between egg cluster counts and estimatesof snail density. The high degree of temporal and spatial variabilityin egg production precludes the use of egg clusters as a reliableindex of apple snail abundance. (Received 15 April 1998; accepted 30 June 1998)     

The North Inlet marsh — estuarine ecosystem: A conceptual approach

The North Inlet marsh — estuarine ecosystem (located at South Carolina, USA) is described via three sub-models: intertidal, benthic-subtidal and water column. The principal storage compartments and fluxes of energy are defined for each submodel. A detailed example of the intertidal oyster subsystem of the intertidal submodel is described. The biological components of the intertidal oyster subsystem of the intertidal submodel is described. The biological components of the oyster community are shown to be stable and a linear systems model of the oyster community is developed. A 1% sensitivity analysis of the intertidal oyster model affords some order in which aspects of the oyster community should be studied.     

Interactive effects of senescence and natural disturbance on the annual survival probabilities of snail kites

Individuals in wild populations face risks associated with both intrinsic (i.e. aging) and external (i.e. environmental) sources of mortality. Condition‐dependent mortality occurs when there is an interaction between such factors; however, few studies have clearly demonstrated condition‐dependent mortality and some have even argued that condition‐dependent mortality does not occur in wild avian populations. Using large sample sizes (2084 individuals, 3746 re‐sights) of individual‐based longitudinal data collected over a 33 year period (1976–2008) on multiple cohorts, we used a capture–mark–recapture framework to model age‐dependent survival in the snail kite Rostrhamus sociabilis plumbeus population in Florida. Adding to the growing amount of evidence for actuarial senescence in wild populations, we found evidence of senescent declines in survival probabilities in adult kites. We also tested the hypothesis that older kites experienced condition‐dependent mortality during a range‐wide drought event (2000–2002). The results provide convincing evidence that the annual survival probability of senescent kites was disproportionately affected by the drought relative to the survival probability of prime‐aged adults. To our knowledge, this is the first evidence of condition‐dependent mortality to be demonstrated in a wild avian population, a finding which challenges recent conclusions drawn in the literature. Our study suggests that senescence and condition‐dependent mortality can affect the demography of wild avian populations. Accounting for these sources of variation may be particularly important to appropriately compute estimates of population growth rate, and probabilities of quasi‐extinctions.