Trait shifts associated with the subshrub life-history strategy in a tropical savanna.

Over the past 10 million years, tropical savanna environments have selected for small growth forms within woody plant lineages. The result has been the evolution of subshrubs (geoxyles), presumably as an adaptation to frequent fire. To evaluate the traits associated with the shift from tree to subshrub growth forms, we compared seed biomass, germination, survival, resprouting, biomass allocation, and photosynthesis between congeneric trees and subshrubs, and quantified phylogenetic conservatism. Despite large differences in adult morphology between trees and subshrub species, the differences are modest in seedlings, and most of the variation in traits was explained by genus, indicating considerable phylogenic conservatism. Regardless, tree seedlings invested more heavily in aboveground growth, compared to subshrubs, which is consistent with the adult strategy of savanna trees, which depend on a large resistant-fire stem. Subshrub seedlings also invest in greater non-structural carbohydrate reserves, likely as an adaptation to the high fire frequencies typical of tropical savannas. The modest differences as seedlings suggest that selective pressures during early development may not have contributed substantially to the evolution of the subshrub growth form and that the distinct allocation and life history must arise later in life. This is consistent with the interpretation that the subshrub growth form arose as a life-history strategy in which maturity is reached at a small stem size, allowing them to reproduce despite repeated fire-induced topkill. The convergent evolution of subshrubs within multiple tree lineages reaffirms the importance of fire in the origin and diversification of the flora of mesic savannas.

Prevalence of hyperinsulinaemia among normozoospermic donors at Medfem Clinic, South Africa.

The aim of this study was to investigate the prevalence of hyperinsulinaemia in a group of normozoospermic donors and the influence of insulin levels on in vitro fertilisation (IVF) outcome. Fasting insulin and 2 h post-eating insulin levels were determined for a group of thirty-four sperm donors. They were divided into three groups according to their insulin profiles. The association between insulin levels and embryo quality was determined in a clinical study for the different groups. The prevalence of raised insulin in the donor group was 44% with a 95% confidence interval of 27.2% and 62.1%. Donors with normal insulin levels produced more good quality blastocysts in the IVF programme than those with abnormal insulin levels. These differences were not statistically significant (P=0.8638). Embryo quality in an IVF programme may be influenced by male insulin levels. The role of insulin in male fertility needs to be investigated.

Long-term observations on mouse strains experimentally infected with Angiostrongylus costaricensis.

BALB/c and C57BL/6 mice were experimentally infected with Angiostrongylus costaricensis and the parasitic parameters and antibody response during the acute and chronic phases of infection were analyzed. Following administration of six third-stage larvae (L3), there was no significant difference in the mean worm recovery or mean larval output. Coinciding with the maturation of worms in infected animals and with the egg output in mesenteric arteries, a strong increase in the humoral immune response was observed in both mouse strains. This response was characterized by a hypergammaglobulinemia, with a predominance of IgA and IgG1 during the acute phase of infection, and IgG1 and total IgE during the patent and post-patent periods. Significantly higher levels of IgM, IgG and IgG1 were found in BALB/c mice compared with C57BL/6 mice. On the other hand, a significantly higher concentration of IgA was detected at 6 and 7 weeks post-infection in C57BL/6 mice compared with BALB/c mice. Specific IgE could not be detected in any of the mouse strains. Our results suggest that immunoglobulins, mainly IgG1, contribute to the outcome of a primary A. costaricensis infection with respect to the period of patency and to mortality during the chronic phase.

Isolation of Angiostrongylus costaricensis first-stage larvae from rodent feces on a Percoll gradient.

Several density gradients were tested for the isolation of parasitic nematode, Angiostrongylus costaricensis, first-stage larvae from rodent feces. With a 45/72% Percoll gradient, 83-99% (89.56+/-6.57%) of the larvae were recovered in a clean preparation.

The granular forms of the leprosy bacillus

The leprosy bacillus, like other acid-fast bacilli, produces in its evolutionary cycle great numbers of granular forms which are found both within the bacilli and as free-lying bodies. These granules constitute an essential phase in its evolution. Among the free-lying forms are those of all sizes down to the limits of visibility, so that it is probable that still smaller, perhaps invisible and filterable forms exist, which may be of special though as yet unknown importance in the pathology and epidemiology of the disease. The supposition is feasible that many of these granular forms are phenomena of degeneration and disintegration, which are determined in part by the defensive substances of the organism and in part by the action of our medicinal products, and especially by the chaulmoogra oil; therefore, their presence can be considered a favorable sign. Howevwe, a careful study of the granular forms suggests that they should not be considered solely as degenerative forms. Evidence is given that in other cases they seem to be especially resistant or young forms, essential for the preservation and perhaps propagation of the microorganism of leprosy. Obviously, the importance of these forms for scientific study and practical work in leprosy cannot be overestimated...