Reproductive biology in Acacia caven (Mol.) Mol. (Leguminosae) in the central region of Argentina

Studies on Acacia caven (Mol.) Mol. in central Argentina indicate that the species is polygamous (andromonoecious), some plants having a high proportion of staminate heads. Though pollen/ovule ratios of flowers, inflorescences and plants are at a level common for 'facultative xenogamic' systems, controlled pollination shows a marked xenogamy. The ratio between pollen grains in the polyad and the maximum number of seeds per pod is close to one. Observations support the idea of the inflorescence as a specialized reproductive unit with gynoecia functioning as fixed modules in which all or none of its ovules develop into seeds. Mass flowering prior to the growing season, the absence of other floral resources in the community, the high degree of fruiting limitations and scarce insect visitation suggest that, as in other Acacia , the reproductive system of Acacia caven involves a great sacrifice of floral resources.     

Tonganoxichnus a new insect trace from the Upper Carboniferous of eastern Kansas

Upper Carboniferous tidal rhythmites of the Tonganoxie Sandstone Member (Stranger Formation) at Buildex Quarry, eastern Kansas, USA, host a relatively diverse arthropod-dominated ichnofauna. Bilaterally symmetrical traces displaying unique anterior and posterior sets of morphological features are well represented within the assemblage. A new ichnogenus, Tonganoxichnus, is proposed for these traces. T. buildexensis, the type ichnospecies, has an anterior region characterized by the presence of a frontal pair of maxillary palp impressions, followed by a head impression and three pairs of conspicuous thoracic appendage imprints symmetrically opposite along a median axis. The posterior region commonly exhibits numerous delicate chevron-like markings, recording the abdominal appendages, and a thin, straight, terminal extension. T. buildexensis is interpreted as a resting trace. A second ichnospecies, T. ottawensis, is characterized by a fan-like arrangement of mostly bifid scratch marks at the anterior area that records the head- and thoracic-appendage backstrokes against the substrate. The posterior area shows chevron-like markings or small subcircular impressions that record the abdominal appendages of the animal, also ending in a thin, straight, terminal extension. Specimens display lateral repetition, and are commonly grouped into twos or threes with a fix point at the posteriormost tail-like structure. T. ottawensis is interpreted as a jumping structure, probably in connection with feeding purposes. The two ichnospecies occur in close association, and share sufficient morphologic features to support the same type of arthropod producer. T. buildexensis closely mimics the ventral anatomy of the tracemaker, whereas T. ottawensis records the jumping abilities of the animal providing significant ethologic and paleoecologic information. The presence of well-differentiated cephalic, thoracic, and abdominal features, particularly in T. buildexensis, resembles the diagnostic tagmosis and segmentation of insects. Detailed analysis of trace morphology and comparison with described Paleozoic insect fossils and extant related forms suggest a monuran as the most likely tracemaker.     

Environmentally induced spatio-temporal variations in the fecundity of brown trout Salmo trutta L.: trade-offs between egg size and number

1. Resident brown trout Salmo trutta in the Esva River basin (north Spain) live in a patchy environment with tracts of riparian forest or meadow along stream banks. This study assessed whether the reproductive traits of brown trout from four contrasting sites reflected site-specific factors.
2. Length at maturity (10.5–11 cm of 1 + individuals) was the same in the four sites examined but slowest growers in slow-growing sub-populations delayed maturity for 1 year relative to fast-growing fish. The analysis of monthly variations in egg size and number suggest that two 'decisions' in two consecutive years are required to complete spawning. The first concerns the number of eggs, determined when trout are still 0 +, and the second concerns egg size.
3. At three sites, egg size and number did not differ significantly between years but highly significant interannual variations were apparent at another site. Fish length was the major determinant of egg size and number at all sites but for any given length, brown trout at sites where the fish exhibited higher growth rates spawned more, but smaller, eggs than those at slow-growing sites. This spatial pattern was identical to the temporal pattern exhibited by trout at another site. The combination of temporal (year-to-year) and spatial (between rivers) variations in egg size and number showed a significant negative correlation, supporting the operation of a trade-off between these two traits.
4. The trade-off between egg size and number seems to be determined by site-specific factors, with slow-growing trout at sites which are fully covered by canopy spawning fewer, but larger, eggs than fast-growers in unshaded sites.     

Inhibition of Early Endosome Fusion by Trypansom cruzi-Infected Macrophage Cytosol

ABSTRACT. Trypanosoma cruzi trypomastigotes survive inside macrophages by promoting fusion between the parasitophorous vacuole and mature host lysosomes upon internalization. Since trypomastigotes can evade the lytic pathway, the earliest steps of endocytosis, such as early endosome fusion, may be affected. To test this hypothesis, we used an in vitro early endosome fusion assay. Our results show that trypomastigote-infected macrophage cytosols cannot promote fusion between early endosomes, compared to mock-infected cytosols (heat-killed trypomastigotes were used in the parasite-macrophage interaction assay). GTPγS addition potentiates the fusogenic activity driven by trypomastigote-infected macrophage cytosol-mediated assays, unlike the biphasic fusogenic effect obtained with GTPγS treatment of macrophage cytosol controls. Calcium-stimulated early endosome fusogenic processes are not affected in the assays mediated by infected macrophage cytosol. We conclude that GTP-regulated factors, and not calcium-regulated elements, are involved in the inhibition of the early endosome fusogenic process by the trypomastigote-infected macrophage cytosol. This primary impediment to the progress of a normal endocytosis may be a relevant step required for the lysosomal recruitment-fusion of the host lysosmes upon trypomastigote infection and further survival of the parasite within its host.     

First record in America of Aedes albopictus naturally infected with dengue virus during the 1995 outbreak at Reynosa, Mexico

Abstract Mosquito collections were conducted during a dengue outbreak in Reynosa, Tamaulipas, Mexico, July-December 1995. A total of 6694 adult mosquitoes (four genera and nine species) were captured, of which 2986 (78.3% females and 21.7% males) were Aedes albopictus and 2339 (39.7% females and 60.3% males) were Ae.aegypti. These two species comprised 84.2% of the total collection. Specimens were grouped into pools, nearly 50% of them processed for detection of virus by cythopathic effect in C6-36 and VERO cell cultures and by haemagglutination test. Five pools gave positive haemagglutin-ation reactions and were examined by immunofluorescence using monoclonal antibodies to flavivirus and to dengue virus. One pool of ten Ae.albopictus males was positive for dengue virus: serotypes 2 and 3 were identified by serotype-specific monoclonal antibodies arid confirmed by RT-PCR. This is the first report of Ae.albopictus naturally infected with dengue virus in America. Also, it is the very first time Ae.albopictus males have been found infected with dengue virus in the wild.     

Nitrogen fixation, stomatal response and transpiration in Medicago sativa, Trifolium repens and T. subterraneum under water stress and recovery

Stomatal behaviour, transpiration and nitrogen fixation were investigated in Medicago sativa L. (cvs. Tierra de Campos and Aragon, Hidalgo-Maynar 1966), Trifolium repens L. (cv. Aberystwyth S-184) and Trifolium subterraneum L. (cv. Clare) subjected to drought by withholding water and then to three days’ recovery after rewatering. Dawn leaf water potential was measured with pressure chamber, stomatal response with a diffusion porometer and nitrogen fixation by using acetylene reduction technique. At low water potentials, the leaf resistance was higher in Medicago than in Trifolium. As water stress developed all species decreased their transpiration, T. subterraneum being the one most affected by moderate deficits. During water stress ‘Tierra de Campos’ always maintained higher acetylene reduction levels than ‘Aragon’ and the Trifolium species, except for the lowest water potentials. During recovery from water stress only ‘Tierra de Campos’ reached predeficit transpiration rates. In ‘Tierra de Campos’ acetylene reduction recovery after rewatering was more rapid and intense than in ‘Aragon’. It is concluded that, of the plants investigated, ‘Tierra de Campos’ was best adapted to water deficits.     

Specificity of Cellular Immune Reactivity to Virus-induced Tumours

SPECIFICITY is one of the chief hallmarks of immune reactions. In many cases, specificity has been defined by reactivity against some antigens and not against others, but the results of direct tests may be misleading. In many cases, in transplantation and tumour immunology, direct reactivity may be absent in spite of the presence of the antigen. With HL-A antigens, the CYNAP phenomenon (cytotoxicity negative, absorption positive) has been described¹. Virus-induced tumours may have relatively small amounts of tumour specific cell surface antigens which are detectable only by absorption tests^2,3. In addition, immune reactions may occur against a particular antigen on one material and against different antigens on another material. With antibody reactions, specificity can be confirmed by the appropriate absorption experiments^4,5. With cellular immune reactions, comparable demonstration of specificity has been very difficult.     

Use of an encounter model to predict size-selective predation by a stream-dwelling cyprinid

1. The increased probability of detection of larger prey in the drift appeared to be the major determinant of prey consumption by red roach (Rutilus arcasi) in an Iberian stream. We developed a model of prey encounter incorporating this factor that explained 68% of the overall variation in the consumption of prey of different size. When the same model was applied to benthic size distributions the variance explained was 16%. 2. Gape-limited ingestion also was a significant factor influencing prey consumption and, when added to the model, the variance explained increased to 85% (32% for the benthos), but its importance was strongly dependent on both: (i) the maximum prey size available and (ii) fish size. 3. The exact shape of red roach reactive fields and, as a consequence, their degree of size-selectivity appeared to vary seasonally and ontogenetically. In summer, younger fish exhibited apparently reduced reactive fields. We hypothesize that this can be the result of factors such as microhabitat shifts or a reduced range of prey sizes.