A New Aspect of Trypanosoma cruzi Life-Cycle in the Invertebrate Host

SYNOPSIS. Trypanosoma cruzi blood trypomastigotes transform, in the stomach of the invertebrate host, into round or pear-shaped forms. A certain number form attached pairs or large masses of aggregated amastigotes. Cytoplasmic bridges and membrane leaks may be observed between apposed parasites. There are fusion of the organisms, an apparent disorganization of the DNA-containing organelles and thickening of the borders of the parasite aggregates. From those borders single or small clumps of flagellates begin to detach and liberate. The meaning of this heretofore overlooked sequence of events as well as the possibility of genetic exchange among the parasites in the early stages of development are discussed.     

A meta‐analysis of leaf‐cutting ant nest effects on soil fertility and plant performance

1. Leaf‐cutting ants (LCAs) are considered as one of the most important agents of soil disturbances that affect vegetation patterns, but these assertions are based on isolated studies or anecdotal data. In this study, meta‐analysis techniques were used to quantitatively analyse the generality of these effects and determine some of their sources of variation. 2. The results reveal the following: (i) LCA nest sites showed higher levels of soil fertility than control sites, but the key source of these nutrients is the refuse material rather than the nest soil itself; (ii) refuse material from external piles tended to be richer in nutrient content than refuse material from internal refuse chambers; (iii) nest sites from temperate habitats showed higher cation content than those located in tropical/subtropical habitats; and (iv) nest sites showed higher plant growth than adjacent non‐nest sites (especially if plants have access to the refuse) but similar plant density and plant richness. 3. As LCAs improve nutrient availability in nest sites through the accumulation of refuse material, the location of the refuse will have a relevant role affecting vegetation. LCA species with external refuse dumps could benefit herbs, early vegetation stages and short‐living plants, whereas those with internal refuse chambers could benefit long‐living, large trees. However, the positive effect on individual plants does not extend to population and community levels. The foraging preferences of ants and the changes in microclimatic conditions around nests could act as selective ecological filters. 4. As refuse material from external piles and nest sites in temperate habitats tend to show higher fertility than refuse material from internal nest chambers and nest sites in tropical/subtropical habitats, LCA species with external refuse dumps in temperate regions could be of particular relevance for nutrient cycling and vegetation patterns.     

Nocturnal resource defence in aphid‐tending ants of northern Patagonia

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The ‘truck‐driver’ effect in leaf‐cutting ants: how individual load influences the walking speed of nest‐mates

The foraging behaviour of social insects is highly flexible because it depends on the interplay between individual and collective decisions. In ants that use foraging trails, high ant flow may entail traffic problems if different workers vary widely in their walking speed. Slow ants carrying extra‐large loads in the leaf‐cutting ant Atta cephalotes L. (Hymenoptera: Formicidae) are characterized as ‘highly‐laden’ ants, and their effect on delaying other laden ants is analyzed. Highly‐laden ants carry loads that are 100% larger and show a 50% greater load‐carrying capacity (i.e. load size/body size) than ‘ordinary‐laden’ ants. Field manipulations reveal that these slow ants carrying extra‐large loads can reduce the walking speed of the laden ants behind them by up to 50%. Moreover, the percentage of highly‐laden ants decreases at high ant flow. Because the delaying effect of highly‐laden ants on nest‐mates is enhanced at high traffic levels, these results suggest that load size might be adjusted to reduce the negative effect on the rate of foraging input to the colony. Several causes have been proposed to explain why leaf‐cutting ants cut and carry leaf fragments of sizes below their individual capacities. The avoidance of delay in laden nest‐mates is suggested as another novel factor related to traffic flow that also might affect load size selection The results of the presennt study illustrate how leaf‐cutting ants are able to reduce their individual carrying performance to maximize the overall colony performance.     

Distribution of Carbohydrates Recognized by the Lectins Euonymus europaeus and Concanavalin A in Monoxenic and Heteroxenic Trypanosomatids

We observed a wide distribution of the carbohydrate epitopes galactosylα(1–3) galactose (galα1–3 gal), α-glucoside, and α-mannoside in mono- and heteroxenic trypanosomatids by using fluorescein-labelled lectins of Euonymus europaeus (EE) and Concanavalin A (Con A) as well as sera from acute chagasic patients who have very high levels of anti-galα(1–3) gal antibodies. The direct fluorescence test for galα1–3 gal with EE was positive at minimum concentrations of 6 μg/ml for heteroxenic trypanosomatids and 0.7 μg/ml for monoxenic ones and for the plant parasite, Phytomonas. On the other hand, heteroxenic trypanosomatids that infect vertebrates bound ten-fold more Con A than monoxenic flagellates and Phytomonas. These data were confirmed in ELISA and Western Blot assays carried out with peroxidase-labelled EE and Con A. Euonymus europaeus recognized several glycoproteins in all trypanosomatids that we tested. Con A, however, recognized a glycoprotein cluster in heteroxenic protozoa, which ranging from 60–120 kDa, seemed to lack monoxenic parasites and Phytomonas. These findings suggest that α-D-mannose and α-D-glucose might play an important role in the interaction between trypanosomatids and vertebrate hosts.     

Cryopreservation of Trypanosoma cruzi Bloodstream Forms*

SYNOPSIS. Recovery rates of T. cruzi bloodstream forms subjected to several methods of cryopreservation in liquid nitrogen and at -73 C are reported. Inoculations of animals with cryopreserved and nonpreserved trypomastigotes revealed that prolonged storage at -196 C apparently did not change the biologic characteristics of different T. cruzi strains. The reproducibility and consistency of results suggest that “cryobanks'’or “reference centers'’may be established.     

Growth-Inhibition Drug Test with Trypanosoma cruzi Culture Forms*

SYNOPSIS. A 48-hr drug screening test is described which evaluates inhibition of exponential growth of T. cruzi culture forms by electronic cell count. About 80% of drugs active in vivo produced a > 50% growth inhibition, whereas among, compounds inactive in vivo, only 19.6% induced such inhibition. Advantages of this test are low cost, rapid results, small amounts of drugs needed, and feasibility without animal facilities. Comparative studies showed that culture forms are not suitable for screening additives to prevènt transmission of T. cruzi by banked blood.     

Mechanism of Acquired Immunity Induced by “Leptomonas pessoai” against Trypanosoma cruzi in Mice*

Living culture forms of “Leptomonas pessoai” cross protected mice against T. cruzi challenge infection. Circulating antibodies have been detected in the immunized mice by immunodiffusion analysis, passive hemagglutination, complement fixation test and antibody binding assay; these antibodies cross reacted with T. cruzi extracts. A cellular immune response was indicated by leucocyte migration inhibition using L. pessoai and T. cruzi antigens, strongly suggesting a role for cell-mediated immunity in the mechanism of protection induced by L. pessoai.