Computer-assisted visualization of the rat epididymis: a methodological study based on paraffin sections autometallographically stained for zinc ions

A concept for the computer-assisted visualization of tubular organs is presented. Unmarked histological zinc-stained serial sections from the epididymis of the Wistar rat were aligned to demonstrate the concept. Virtual images were made through the aligned sections and served as controls for the alignment process. Animation of the serial sections and the virtual images revealed new information about the structure of the organ under investigation. The analysis was used to upgrade the anatomical knowledge of rat epididymis by describing how the epididymal duct runs through the structure. The proximal parts of the epididymis contain large communicating septa of connective tissue dividing the caput and the upper part of the corpus epididymidis into segments. The tortuousness was high in the caput with many turns within a small area of the epididymis, whereas longer loops were found in the lower part of the corpus and cauda epididymidis. The tube of the vas deferens was found to become an integrated part of the ductal system in the cauda epididymidis, although it was histologically easy to distinguish from the epididymal duct. The total number of cross-sections of the ductus epididymidis in the 2254, 15-mu m-thick, tissue sections analysed was 104 700, giving a minimum length of the ductal system of 1.5 m. © 1998 Chapman & Hall     

Intrinsic competition between primary hyperparasitoids of the solitary endoparasitoid Cotesia rubecula

1. In nature, competitive interactions occur when different species exploit similar niches. Parasitic wasps (parasitoids) often have narrow host ranges and need to cope with competitors that use the same host species for development of their offspring. When larvae of different parasitoid species develop in the same host, this leads to intrinsic and often contest competition. Thus far, most studies on intrinsic competition have focused on primary parasitoids. However, competition among primary hyperparasitoids, parasitic wasps that use primary parasitoids as a host, has been little studied. 2. This study investigated intrinsic competition between two primary hyperparasitoids, the gregarious Baryscapus galactopus and the solitary Mesochorus gemellus, which lay their eggs in primary parasitoid larvae of Cotesia rubecula, while those in turn are developing inside their herbivore host, Pieris rapae. The aims were to identify: (i) which hyperparasitoid is the superior competitor; and (ii) whether oviposition sequence affects the outcome of intrinsic competition. 3. The results show that B. galactopus won 70% of contests when the two hyperparasitoids parasitised the host at the same time, and 90% when B. galactopus oviposited first. When M. gemellus had a 48 h head start, the two hyperparasitoids had an equal chance to win the competition. This suggests that B. galactopus is an intrinsically superior competitor to M. gemellus. Moreover, the outcome of competition is affected by time lags in oviposition events. 4. In contrast to what has been reported for primary parasitoids, we found that a gregarious hyperparasitoid species had a competitive advantage over a solitary species.     

Therapeutic Use of Antimelanoma Monoclonal Antibodies

Monoclonal antibodies (MAb) to tumor-associated antigens are attracting much attention for tumor therapy. Melanomas belong to the tumors most studied in this respect, and several melanoma-associated antigens have been studied in great detail. These include the melanoma-associated glycoprotein p97, the melanoma-associated proteoglycan, and glycolipid antigens. Although none of the antigens is absolutely specific for tumor, the degree of relative specificity appears to be sufficient to use several of the melanoma antigens as therapeutic “targets”. Antimelanoma MAb can be applied therapeutically in several ways. The most straightforward approach is use of MAb without further modification. MAb which kill melanoma cells in the presence of human serum as the source of complement or mediate antibody-dependent cellular cytotoxicity with human natural killer (NK) cells or macrophages as effectors are logical choices for this. Some cases of partial or even complete regression of metastatic melanoma have been observed in patients treated with such MAb. Combinations of such MAb with interleukin 2 (IL-2) or other immunological response modifiers are of great interest. Alternatively, one may use antimelanoma MAb (or fragments prepared from MAb) as carriers of antitumor agents, including radioactive isotopes, toxins, or chemotherapeutic drugs. Although it is premature to make any conclusions about the efficacy of such conjugates, we are optimistic that it will be feasible by using the right combination of MAb and antitumor agent to achieve therapeutic benefit. Another approach is to develop therapeutic “vaccines” for active immunization, once an antigen characterized by using a MAb has proven to have a relatively high level of tumor selectively. Anti-idiotypic antibodies and live recombinant viruses inducing tumor antigen expression in infected cells provide alternative strategies to this approach.     

Reliability of placental scar counts in the Red fox {Vulpes vulpes L.) with special reference to fading of the scars

The use of placental scar counts in determining litter size and pregnancy rate among Red foxes ( Vulpes vulpes L.) is reviewed. There is no experimental material to test the validity of the method, although many authors have discussed it. Recent workers have (1) included uteri from vixens killed later in the season and, (2) become more concerned about effects of resorptions and/or abortions on scar counts, as well as the possibility of scars persisting from earlier pregnancies. In the present study, scar counts overestimated numbers of persisting corpora lutea to a higher degree in old vixens than in yearlings; and scars were shown to fade over winter. Estimates of frequency of breeding among females, based on various combinations of placental scars of different shades, and on date of death, are discussed. The relation between number of scars of different shades, date of death and known minimum litter size in three wild and one captive vixen is compared with the foregoing. Counts of all scars evidently overestimate litter size at birth and breeding frequency, probably because some scars originate at resorption sites and others persist from earlier pregnancies. Only dark scars should be counted early in the season, but those of increasingly lighter shade should be included as winter progresses. A guide to counting placental scars over winter is presented.     

Habitat invasion risk assessment based on Landsat 5 data,exemplified by the shrub Rosa rubiginosa in southern Argentina

Prediction of invasive species spread helps to plan management actions. We performed a risk assessment by quantifying habitat invasibility, predicted the potential distribution of an invasive species using the Maxent modelling program and confirmed patterns using detailed field studies. Our study was conducted in southern Argentina, Patagonia, where large areas are already invaded by the European shrub Rosa rubiginosa. A total of 163 R. rubiginosa locations served as ground truth data, and predictors were obtained from the spaceborne sensor Landsat 5. Based on the Maxent Method (area under the receiver operating characteristic curve 0.8), the habitat invasibility map covered about 5000 km². Our model revealed that R. rubiginosa has the potential to invade 36% of the area along a steep precipitation gradient (target region 600–1400 mm per year). The Tasseled Cap brightness index and the normalized vegetation index explained most of the variance in our model, followed by the Tasseled Cap greenness and wetness indices, which can be interpreted as indicators of disturbance. Highest levels of invasibility were predicted for urban areas, along roads and rivers, on pastures, in Austrocedrus chilensis forests and inside Nothofagus dombeyi forest gaps. Detailed field assessments of rose cover performed in seven habitat types supported these results: rose cover significantly decreased with increasing tree cover (P < 0.01). Our data revealed that the occurrence of R. rubiginosa is not connected to a certain habitat type, but that it thrives in open patches following habitat disturbance. Our approach is a widely applicable, cost‐free remote sensing method that can serve as a risk assessment tool for alien plant species invasion of habitats.     

A radiotelemetry study of habitat use by the exotic Ring‐necked Parakeet Psittacula krameri in Belgium

Little is known about the foraging ecology of invasive bird species in Europe. We used radio‐telemetry to assess home‐ranges of breeding male Ring‐necked Parakeets in Brussels. Results indicate that parakeets primarily forage in parks and gardens while avoiding forests. This can probably be explained by the higher food availability in anthropogenic habitats and fits a general pattern that invasive species generally select heavily altered environments.     

Ambiguous climate impacts on competition between submerged macrophytes and phytoplankton in shallow lakes

1. Shallow lakes may switch from a state dominated by submerged macrophytes to a phytoplankton‐dominated state when a critical nutrient concentration is exceeded. We explore how climate change may affect this critical nutrient concentration by linking a graphical model to data from 83 lakes along a large climate gradient in South America. 2. The data indicate that in warmer climates, submerged macrophytes may tolerate more underwater shade than in cooler lakes. By contrast, the relationship between phytoplankton biomass [approximated by chlorophyll‐a (chl‐a) or biovolume] and nutrient concentrations did not change consistently along the climate gradient. In warmer climates, the correlation between phytoplankton biomass and nutrient concentrations was overall weak, especially at low total phosphorus (TP) concentrations where the chl‐a/ TP ratio could be either low or high. 3. Although the enhanced shade tolerance of submerged plants in warmer lakes might promote the stability of their dominance, the potentially high phytoplankton biomass at low nutrient concentrations suggests an overall low predictability of climate effects. 4. We found that near‐bottom oxygen concentrations are lower in warm lakes than in cooler lakes, implying that anoxic P release from eutrophic sediment in warm lakes likely causes higher TP concentrations in the water column. Subsequently, this may lead to a higher phytoplankton biomass in warmer lakes than in cooler lakes with similar external nutrient loadings. 5. Our results indicate that climate effects on the competitive balance between submerged macrophytes and phytoplankton are not straightforward.     

Substantial differences in littoral fish community structure and dynamics in subtropical and temperate shallow lakes

1. Fish play a key role in the functioning of temperate shallow lakes by affecting nutrient exchange among habitats as well as lake trophic structure and dynamics. These processes are, in turn, strongly influenced by the abundance of submerged macrophytes, because piscivorous fish are often abundant at high macrophyte density. Whether this applies to warmer climates as well is virtually unknown. 2. To compare fish community structure and dynamics in plant beds between subtropical and temperate shallow lakes we conducted experiments with artificial submerged and free‐floating plant beds in a set of 10 shallow lakes in Uruguay (30°–35°S) and Denmark (55°–57°N), paired along a gradient of limnological characteristics. 3. The differences between regions were more pronounced than differences attributable to trophic state. The subtropical littoral fish communities were characterised by higher species richness, higher densities, higher biomass, higher trophic diversity (with predominance of omnivores and lack of true piscivores) and smaller body size than in the comparable temperate lakes. On average, fish densities were 93 ind. m⁻² (±10 SE) in the subtropical and 10 ind. m⁻² (±2 SE) in the temperate lakes. We found a twofold higher total fish biomass per unit of total phosphorus in the subtropical than in the temperate lakes, and as fish size is smaller in the former, the implication is that more energy reaches the littoral zone fish community of the warmer lakes. 4. Plant architecture affected the spatial distribution of fish within each climate zone. Thus, in the temperate zone fish exhibited higher densities among the artificial free‐floating plants while subtropical fish were denser in the artificial submerged plant beds. These patterns appeared in most lakes, regardless of water turbidity or trophic state. 5. The subtropical littoral fish communities resembled the fish communities typically occurring in temperate eutrophic and hypertrophic lakes. Our results add to the growing evidence that climate warming may lead to more complex and omnivory‐dominated food webs and higher density and dominance of smaller‐sized fish. This type of community structure may lead to a weakening of the trophic cascading effects commonly observed in temperate shallow lakes and a higher risk of eutrophication.