Morphological Changes in the Midgut of Aedes aegypti L. (Diptera: Culicidae) Larvae Following Exposure to an Annona coriacea (Magnoliales: Annonaceae) Extract

Bioinsecticides are important in the control of disease vectors, but data regarding their physiological effects on target insects are incomplete. This study describes morphological changes that occur in the midgut of third instar Aedes aegypti L. (Diptera: Culicidae) following treatment with a methanolic extract of Annona coriacea (Magnoliales: Annonaceae). Dissected midguts were subdivided into anterior and posterior regions and analyzed by light and scanning electron microscopy. Insects exposed to the extract displayed intense, destructive cytoplasmic vacuolization in columnar and regenerative midgut cells. The apical surfaces of columnar cells exhibited cytoplasmic protrusions oriented toward the lumen, suggesting that these cells could be involved in apocrine secretory processes and/or apoptosis. We report that A. coriacea extracts induced morphological alterations in the midgut of A. aegypti midgut larvae, supporting the use of plant extracts for control of the dengue vector.     

Evidence for diet partitioning among three coexisting native freshwater fishes in South Africa's Cape Fold Ecoregion

The partitioning of limited resources commonly explains how different species can coexist within the same ecological community. In this 2010 study, the diets of three coexisting freshwater fishes (Cape galaxias Galaxias zebratus, n = 27; Cape kurper Sandelia capensis, n = 60; Breede River redfin Pseudobarbus burchelli, n = 77) were characterised and compared in three headwater streams in South Africa's Cape Fold Ecoregion using gut contents and stable isotope analyses. These data were analysed to ascertain whether the three species exploit distinct trophic niches. Both approaches provided evidence that these species occupy different trophic niches, though with some overlap. However, dietary differences among sites were not consistent and were probably influenced by site-specific factors like resource availability. Pseudobarbus burchelli had a broader niche breadth at Tierkloof Stream than the other two species, but not at Waaihoek or Tierstel Streams. Our results also suggest that P. burchelli consumed a more omnivorous diet than do the other two species, whereas S. capensis occupied a higher trophic position than the other two species and consumed vertebrates. Our findings suggest that these species occupy non-equivalent feeding niches in Cape Fold Ecoregion headwater streams, and that diet partitioning might facilitate their coexistence in these systems.     

The Cell Tropism of Human Immunodeficiency Virus Type 1 Determines the Kinetics of Plasma Viremia in SCID Mice Reconstituted with Human Peripheral Blood Leukocytes

Most individuals infected with human immunodeficiency virus type 1 (HIV-1) initially harbor macrophage-tropic, non-syncytium-inducing (M-tropic, NSI) viruses that may evolve into T-cell-tropic, syncytium-inducing viruses (T-tropic, SI) after several years. The reasons for the more efficient transmission of M-tropic, NSI viruses and the slow evolution of T-tropic, SI viruses remain unclear, although they may be linked to expression of appropriate chemokine coreceptors for virus entry. We have examined plasma viral RNA levels and the extent of CD4⁺ T-cell depletion in SCID mice reconstituted with human peripheral blood leukocytes following infection with M-tropic, dual-tropic, or T-tropic HIV-1 isolates. The cell tropism was found to determine the course of viremia, with M-tropic viruses producing sustained high viral RNA levels and sparing some CD4⁺ T cells, dual-tropic viruses producing a transient and lower viral RNA spike and extremely rapid depletion of CD4⁺ T cells, and T-tropic viruses causing similarly lower viral RNA levels and rapid-intermediate rates of CD4⁺ T-cell depletion. A single amino acid change in the V3 region of gp120 was sufficient to cause one isolate to switch from M-tropic to dual-tropic and acquire the ability to rapidly deplete all CD4⁺ T cells.The envelope gene of human immunodeficiency virus type 1 (HIV-1) determines the cell tropism of the virus (11, 32, 47, 62), the use of chemokine receptors as cofactors for viral entry (4, 17), and the ability of the virus to induce syncytia in infected cells (55, 60). Cell tropism is closely linked to but probably not exclusively determined by the ability of different HIV-1 envelopes to bind CD4 and the CC or the CXC chemokine receptors and initiate viral fusion with the target cell. Macrophage-tropic (M-tropic) viruses infect primary cultures of macrophages and CD4⁺ T cells and use CCR5 as the preferred coreceptor (2, 5, 15, 23, 26, 31). T-cell-tropic (T-tropic) viruses can infect primary cultures of CD4⁺ T cells and established T-cell lines, but not primary macrophages. T-tropic viruses use CXCR4 as a coreceptor for viral entry (27). Dual-tropic viruses have both of these properties and can use either CCR5 or CXCR4 (and infrequently other chemokine receptors [25]) for viral entry (24, 37, 57). M-tropic viruses are most frequently transmitted during primary infection of humans and persist throughout the duration of the infection (63). Many, but not all, infected individuals show an evolution of virus cell tropism from M-tropic to dual-tropic and finally to T-tropic with increasing time after infection (21, 38, 57). Increases in replicative capacity of viruses from patients with long-term infection have also been noted (22), and the switch to the syncytium-inducing (SI) phenotype in T-tropic or dual-tropic isolates is associated with more rapid disease progression (10, 20, 60). Primary infection with dual-tropic or T-tropic HIV, although infrequent, often leads to rapid disease progression (16, 51). The viral and host factors that determine the higher transmission rate of M-tropic HIV-1 and the slow evolution of dual- or T-tropic variants remain to be elucidated (4).These observations suggest that infection with T-tropic, SI virus isolates in animal model systems with SCID mice grafted with human lymphoid cells or tissue should lead to a rapid course of disease (1, 8, 44–46). While some studies in SCID mice grafted with fetal thymus and liver are in agreement with this concept (33, 34), our previous studies with the human peripheral blood leukocyte-SCID (hu-PBL-SCID) mouse model have shown that infection with M-tropic isolates (e.g., SF162) causes more rapid CD4⁺ T-cell depletion than infection with T-tropic, SI isolates (e.g., SF33), despite similar proviral copy numbers, and that this property mapped to envelope (28, 41, 43). However, the dual-tropic 89.6 isolate (19) caused extremely rapid CD4⁺ T-cell depletion in infected hu-PBL-SCID mice that was associated with an early and transient increase in HIV-1 plasma viral RNA (29). The relationship between cell tropism of the virus isolate and the pattern of disease in hu-PBL-SCID mice is thus uncertain. We have extended these studies by determining the kinetics of HIV-1 RNA levels in serial plasma samples of hu-PBL-SCID mice infected with primary patient isolates or laboratory stocks that differ in cell tropism and SI properties. The results showed significant differences in the kinetics of HIV-1 replication and CD4⁺ T-cell depletion that are determined by the cell tropism of the virus isolate.     

Inheritance of fertility in broiler chickens

Background

The fertility of a chicken''s egg is a trait which depends on both the hen that lays the egg and on her mate. It is also known that fertility of an individual changes over the laying period.

Methods

Longitudinal models including both random genetic and permanent environmental effects of both the female and her male mate were used to model the proportion of fertile eggs in a pedigree broiler population over the ages 29-54 weeks.

Results

Both the male and the female contribute to variation in fertility. Estimates of heritability of weekly records were typically 7% for female and 10% for male contributions to fertility. Repeatability estimates ranged from 24 to 33%, respectively. The estimated genetic variance remained almost constant for both sexes over the laying period and the genetic correlations between different ages were close to 1.0. The permanent environment components increased substantially towards the end of the analyzed period, and correlations between permanent environment effects at different ages declined with increasing age difference The heritability of mean fertility over the whole laying period was estimated at 13% for females and 17% for males. A small positive correlation between genetic effects for male and female fertility was found.

Conclusion

Opportunities to improve fertility in broiler stocks by selection on both sexes exist and should have an impact throughout the laying period.     

Genetic heterogeneity of residual variance in broiler chickens

Aims were to estimate the extent of genetic heterogeneity in environmental variance. Data comprised 99 535 records of 35-day body weights from broiler chickens reared in a controlled environment. Residual variance within dam families was estimated using ASREML, after fitting fixed effects such as genetic groups and hatches, for each of 377 genetically contemporary sires with a large number of progeny (> 100 males or females each). Residual variance was computed separately for male and female offspring, and after correction for sampling, strong evidence for heterogeneity was found, the standard deviation between sires in within variance amounting to 15–18% of its mean. Reanalysis using log-transformed data gave similar results, and elimination of 2–3% of outlier data reduced the heterogeneity but it was still over 10%. The correlation between estimates for males and females was low, however. The correlation between sire effects on progeny mean and residual variance for body weight was small and negative (-0.1). Using a data set bigger than any yet presented and on a trait measurable in both sexes, this study has shown evidence for heterogeneity in the residual variance, which could not be explained by segregation of major genes unless very few determined the trait.