Postembryonic development of Paracentrophyes praedictus (Homalorhagida): neoteny questionable among the Kinorhyncha

The postembryonic ontogeny of the kinorhynch Paracentrophyes praedictus is described by light microscopy and scanning electron microscopy. The development of head scalids and trunk Characteristics has been studied. The first of 6 juvenile stages possesses 11 segments already. One segment each is added both in stages 2 and 5. The number of head scalids increases during development. Every scalid becomes visible as a spinose anlage in one stage and differentiates in the next stage. All head scalids in stage 1 represent anlagen of scalids. Late juvenile stages J-5 and J-6 express two different scalid patterns which do not seem to depend on the gender. Scalids and trunk segments develop in a subfrontal and a subcaudal growing zone, respectively. The presumed neotenic status of P. praedictus is rejected because this species exhibits the same number of juvenile stages as observed in all other Kinorhyncha studied. It is suggested that a weakly sclerotized, juvenile-like trunk cuticle as found, e.g. in adult P. praedictus represents the plesiomorphic characteristic within the Kinorhyncha; a thickened cuticle has probably evolved independently within both the cyclorhagid and the homalorhagid Kinorhyncha.     

Enrichment of human bone marrow mononuclear phagocytes and characterization of macrophage subpopulations by immunoenzymatic double staining

In order to isolate and enrich bone marrow mononuclear phagocytes, we performed magnetic-activated cell sorting using beads coupled to a monoclonal antibody directed against the monocyte/macrophage surface molecule CD14. Co-localization of antigens in single cells was achieved by combining an alkaline phosphatase--anti-alkaline phosphatase and an avidin--biotin complex immunoassay, avoiding the use of peroxidase. Bone marrow macrophages were first labelled by the monoclonal antibody PG-M1 (anti-CD68). Subsequently, cytoplasmic and/or surface double staining by the monoclonal antibodies against HLA-DR and Mac-2 antigen or the lectin GSA-I-B4 was carried out. Whereas HLA-DR was co-expressed by the great majority of PG-M1+ macrophages (84.9% +/- 6.9%), only a subpopulation exhibited Mac-2 (69.9% +/- 5.9%) antigen or galactoside structures detected by GSA-I-B4 (65.0% +/- 6.7%). The latter result differed only slightly from the percentage of GSA-I-B+4 macrophages determined in a previous comparative immunomorphometrical study. Therefore, using our method of isolation and enrichment by magnetic-activated cell sorting, only a negligible portion of macrophages is apparently stimulated, as shown by GSA-I-B4 staining. This methodology seems to be a valuable tool for further studies on the monocyte--macrophage system. © 1998 Chapman & Hall     

Preparation, Properties, and Composition of Nereis vitellin, the Yolk Protein of the Annelid, Nereis virens

In the literature, oogenesis in nereid annelids is considered to be a model system because, unlike other system studied, nereid oocytes are thought to synthesize the bulk of their yolk protein themselves. As the first step to test the validity of this hypothesis, nereid yolk protein was characterized biochemically. Vitellin, the main fraction of the soluble yolk proteins, was prepared from Nereis virens oocytes. Preparation, purification, and some physical characteristics of this green-colored protein Nereis vitellin are described. The molecular weight was determined by gel chromatography as 420,000 daltons. With regard to the amino acid composition, Nereis vitellin was found to resemble both insect vitellins and an average protein, as defined by other authors. Methionine and cysteine were found in traces only. By staining procedures, Nereis vitellin was characterized as lipoglycoprotein. Nereis vitellin was also prepared from the coelomic fluid of gravid females of Nereis virens .     

A model approach to planktonic stoichiometry and consumer-resource stability

1. The model explores stoichiometric feedback effects between an alga and a grazer ( Daphnia ) in a simplified chemostat-type system in stagnant conditions or with fixed dilution rate.
2. When running the model with fixed stoichiometry and P-sufficient food, the grazer with highest requirements for phosphorus (P) will exert the most efficient control of algal biomass owing to more P being allocated to zooplankton biomass and less P recycled.
3. When including potential P-limitation of the grazer, the grazer with high P requirements (high P : C ratio) will be the least efficient grazer in a system with fluctuating and temporarily low P : C ratio in algae ( Q _a).
4. Qualitatively deficient food will yield decreased growth efficiency in zooplankton. As Q _a decreases, the grazer isocline for zero net growth is shifted upwards, and the required algal biomass for positive growth increases. There may then be a critical level of Q _a below which the grazer with high P : C suffers negative population growth regardless of algal biomass. In cases with low minimum Q _a and a P-demanding grazer, this may cause the system to enter an irreversible stage with high biomass of P-deficient phytoplankton which do not support zooplankton growth.
5. Cumulative primary production for scenarios with continuous P input is, in general, higher the more Q _a is allowed to drop below saturation values, and highest when this is combined with a grazer with a high P : C ratio. The lower growth rate of P-deficient phytoplankton was compensated for by reduced success of the P-limited grazer, yielding low grazing pressure and resulting in larger phytoplankton biomass.     

Wildlife and climate change: assessing the sensitivity of selected species to simulated doubling of atmospheric CO2

We explored, using computer simulations, the sensitivity of four mammal species (elk, Cervus canadensis ; white-tailed deer, Odocoileus virginianus ; Columbian ground squirrel, Spermophilus columbianus ; and chipmunk, Tamias striatus ) within the continental USA to the effect of anticipated levels of global climate change brought about by a doubling of atmospheric CO₂. Sensitivity to the direct effects of climate change were evaluated using a climate-space approach to delineate the range of thermal conditions tolerable by each species. Sensitivity to indirect effects were evaluated by quantifying the association of each species to the current vegetation distribution within the continental USA and using this association to assess whether wildlife species distributions might shift in response to vegetation shifts under climate change. Results indicate that altered thermal conditions alone should have little or no effect on the wildlife species' distributions as physiological tolerance to heat load would allow them to survive. Analyses of the effects of vegetation change indicate that deer and chipmunks should retain their current distributions and possibly expand westward in the USA. For Elk and ground squirrels, there is a possibility that their current distributions would shrink and there is little possibility that each species would spread to new regions. This work emphasizes that the distributions of the four mammalian species are likely to be influenced more by vegetation changes than by thermal conditions. Future efforts to understand the effects of global change on wildlife species should focus on animal–habitat and climate–vegetation linkages.