Penetration of the Mosquito (Aedes aegypti) Midgut Wall by the Ookinetes of Plasmodium gallinaceum

ABSTRACT We observed Plasmodium gallinaceum ookinetes in both intracellular and intercellular positions in the midgut epithelium of the mosquito Aedes aegypti. After epithelial cell invasion intracellular ookinetes lacked a parasitophorous vacuolar membrane and were surrounded solely by their own pellicle. Thus, the ookinete in the midgut epithelium of the mosquito differs from erythrocytic and hepatic stages in that the parasite in the vertebrate host is surrounded by a vacuole. The midgut epithelial cytoplasm around the apical end of invading ookinetes was replaced by fine granular material deprived of normal organelles. Membranous structure was observed within the fine granular area. Most ookinetes were seen intracellularly on the luminal side and intercellularly on the haemocoel side of the midgut epithelial cells. These observations suggest that the ookinete first enters into the midgut epithelial cell, then exits to the space between the epithelial cells and moves to the basal lamina where the ookinete develops to the oocyst.     

The Radial and Longitudinal Path of Ion Movement in Roots

The existence of a barrier to lateral outward diffusion of ions from roots was demonstrated quantitatively and by autoradiography. Ions applied to the apical zone were excreted through the basal cut end with no lateral outward diffusion from the central zone. The ions moving through the conducting tissues showed no leakage to the external solution regardless whether the treatment roots came from seedlings grown under low or high salt conditions. However, when dinitrophenol (DNP) was also applied to the central zone in the external salt solution, leakage of apically applied calcium occurred from the conducting tissues. Autoradiographic studies with labeled calcium suggested that the endodermal layer was an effective barrier preventing the lateral outward diffusion of ions. The ions moved longitudinally through the stele. In the stelar tissues the autoradiographic studies failed to detect the presence of any radioactive calcium in the central duct and in the mature xylem vessels, although high concentrations of labeled ions were found in the living cells of the stele, particularly the xylem parenchyma. It is suggested that xylem parenchyma cells may be involved in the longitudinal transport of ions.     

Identification of sibling mice species (genus Mus) by a simple immunological test

An immunological test that can be made on living animals is developed to identify M. m. musculus mice from the two other short-tailed mice ( M. spicilegus and M. spretoides ) occurring in Eastern Europe. This test uses fractionated albumin antiserum as an immunological marker and is performed using dot-blot immunoassay. One hundred and twelve animals belonging to the three species and originating from wild-caught mice and from laboratory strains were tested. All the M. m. musculus mice were correctly identified with this test. Owing to its simplicity and reliability, this test will be very useful in field surveys, particularly in the zone of sympatry between M. m. musculus and M. spicilegus .     

The Challenges of Living in Hypoxic and Hypercapnic Aquatic Environments

Organisms living in coastal waters, and especially estuaries,have long been known to have behavioral or physiological mechanismsthat enable them toexist in water containing low amounts ofoxygen. However, the respiratory consumption of oxygen thatgenerates hypoxia is also responsible for producing significantamounts of carbon dioxide. An elevation of carbon dioxide pressurein water will cause a significant acidosis in most aquatic organisms.Thus, the combination of low oxygen and elevated carbon dioxidethat occurs in estuaries represents a significant environmentalchallenge to organisms living in this habitat. Organisms maymaintain oxygen uptake in declining oxygen conditions by usinga respiratory pigment and/or by making adjustments in the convectiveflow of water and blood past respiratory surfaces (i.e., increasecardiac output and ventilation rate). Severe hypoxia may resultin an organism switching partially or completely to anaerobicbiochemical pathways to sustain metabolic rate. There is alsoevidence to suggest that organisms lower their metabolism duringhypoxic stress. Elevated water CO₂ (hypercapnia) produces anacidosis in the tissues of organisms that breathe it. This acidosismay be wholly or partially compensated (i.e., mechanisms returnpH to pre-exposure levels), or may be uncompensated. Some studieshave examined the effects on organisms of exposure simultaneouslyto hypoxia and hypercapnia. This article reviews some of thespecific adaptations and responses of organisms to low oxygen,to high carbon dioxide, and to the cooccurrence of low oxygenand high carbon dioxide     

Isolation and cross‐familial amplification of 41 microsatellites for the brook charr (Salvelinus fontinalis)

The brook charr (Salvelinus fontinalis; Osteichthyes: Salmonidae) is a phenotypically diverse fish species inhabiting much of North America. But relatively few genetic diagnostic resources are available for this fish species. We isolated 41 microsatellites from S. fontinalis polymorphic in one or more species of salmonid fish. Thirty‐seven were polymorphic in brook charr, 15 in the congener Arctic charr (Salvelinus alpinus) and 14 in the lake charr (Salvelinus namaycush). Polymorphism was also relatively high in Oncorhynchus, where 21 loci were polymorphic in rainbow trout (Oncorhynchus mykiss) and 16 in cutthroat trout (Oncorhynchus clarkii) but only seven and four microsatellite loci were polymorphic in the more distantly related lake whitefish (Coregonus clupeaformis) and Atlantic salmon (Salmo salar), respectively. One duplicated locus (Sfo228Lav) was polymorphic at both duplicates in S. fontinalis.     

Photodegradation leads to increased carbon dioxide losses from terrestrial organic matter

CO₂ production in terrestrial ecosystems is generally assumed to be solely biologically driven while the role of abiotic processes has been largely overlooked. In addition to microbial decomposition, photodegradation – the direct breakdown of organic matter (OM) by solar irradiance – has been found to contribute to litter mass loss in dry ecosystems. Previous small‐scale studies have shown that litter degradation by irradiance is accompanied by emissions of CO₂. However, the contribution of photodegradation to total CO₂ losses at ecosystems scales is unknown. This study determined the proportion of the total CO₂ losses caused by photodegradation in two ecosystems: a bare peatland in New Zealand and a seasonally dry grassland in California. The direct effect of solar irradiance on CO₂ production was examined by comparing daytime CO₂ fluxes measured using eddy covariance (EC) systems with simultaneous measurements made using an opaque chamber and the soil CO₂ gradient technique, and with night‐time EC measurements under the same soil temperature and moisture conditions. In addition, a transparent chamber was used to directly measure CO₂ fluxes from OM caused by solar irradiance. Photodegradation contributed 19% of the annual CO₂ flux from the peatland and almost 60% of the dry season CO₂ flux from the grassland, and up to 62% and 92% of the summer mid‐day CO₂ fluxes, respectively. Our results suggest that photodegradation may be important in a wide range of ecosystems with exposed OM. Furthermore, the practice of partitioning daytime ecosystem CO₂ exchange into its gross components by assuming that total daytime CO₂ losses can be approximated using estimates of biological respiration alone may be in error. To obtain robust estimates of global ecosystem–atmosphere carbon transfers, the contribution of photodegradation to OM decomposition must be quantified for other ecosystems and the results incorporated into coupled carbon–climate models.     

Tug of war between continental gene flow and rearing site philopatry in a migratory bird: the sex-biased dispersal paradigm reconsidered

Nonrandom dispersal has been recently advanced as a mechanism promoting fine-scale genetic differentiation in resident populations, yet how this applies to species with high rates of dispersal is still unclear. Using a migratory species considered a classical example of male-biased dispersal (the greater snow goose, Chen caerulescens atlantica ), we documented a temporally stable fine-scale genetic clustering between spatially distinct rearing sites (5–30 km apart), where family aggregates shortly after hatching. Such genetic differentiation can only arise if, in both sexes, dispersal is restricted and nonrandom, a surprising result considering that pairing occurs among mixed flocks of birds more than 3000 km away from the breeding grounds. Fine-scale genetic structure may thus occur even in migratory species with high gene flow. We further show that looking for genetic structure based on nesting sites only may be misleading. Genetically distinct individuals that segregated into different rearing sites were in fact spatially mixed during nesting. These findings provide new, scale-dependent links between genetic structure, pairing, and dispersal and show the importance of sampling different stages of the breeding cycle in order to detect a spatial genetic structure.     

The ghost of hybrids past: fixation of arctic charr (Salvelinus alpinus) mitochondrial DNA in an introgressed population of lake trout (S. namaycush)

Complete fixation of arctic charr ( Salvelinus alpinus ) mitochondrial DNA (mtDNA) was observed in a southern Québec population of lake trout ( S. namaycush ). This introgressed population otherwise appeared to be normal with regard to lake trout morphology and three species-diagnostic microsatellite loci. Arctic charr do not occur in the area, suggesting that the hybridization event was prehistoric. Of several possible hypotheses, the most plausible explanation for this aberrant population is that hybridization occurred in situ soon after deglaciation, with repeated backcrossing of hybrids with lake trout. Fixation of S. alpinus mtDNA in the population may have occurred either by chance (drift) or selection, although indirect evidence and data from similarly introgressed brook trout ( S. fontinalis ) populations in the region suggest that selection favouring the S. alpinus mitochondrial type and/or associated nuclear genes may have been involved.