Regeneration of Juvenile Woody Plants after Fire in a Seasonally Dry Tropical Forest of Southern India

Woody tree species in seasonally dry tropical forests are known to have traits that help them to recover from recurring disturbances such as fire. Two such traits are resprouting and rapid post‐fire growth. We compared survival and growth rates of regenerating small‐sized individuals (juveniles) of woody tree species after dry season fire (February–March) at eight adjacent pairs of burnt and unburnt transects in a seasonally dry tropical forest in southern India. Juveniles were monitored at 3‐mo intervals between August 2009 and August 2010. High juvenile survivorship (>95%) was observed in both burnt and unburnt areas. Growth rates of juveniles, analyzed at the community level as well as for a few species individually (especially fast‐growing ones), were distinctly higher in burnt areas compared to unburnt areas after a fire event, particularly during the pre‐monsoon season immediately after a fire. Rapid growth by juveniles soon after a fire may be due to lowered competition from other vegetative forms such as grasses, possibly aided by the availability of resources stored belowground. Such an adaptation would allow a juvenile bank to be retained in the understory of a dry forest, from where individuals can grow to a possible fire‐tolerant size during favorable conditions.     

Lantana camara L. (Verbenaceae) invasion along streams in a heterogeneous landscape

Streams are periodically disturbed due to flooding, act as edges between habitats and also facilitate the dispersal of propagules, thus being potentially more vulnerable to invasions than adjoining regions. We used a landscape-wide transect-based sampling strategy and a mixed effects modelling approach to understand the effects of distance from stream, a rainfall gradient, light availability and fire history on the distribution of the invasive shrub Lantana camara L.(lantana) in the tropical dry forests of Mudumalai in southern India. The area occupied by lantana thickets and lantana stem abundance were both found to be highest closest to streams across this landscape with a rainfall gradient. There was no advantage in terms of increased abundance or area occupied by lantana when it grew closer to streams in drier areas as compared to moister areas. On an average, the area covered by lantana increased with increasing annual rainfall. Areas that experienced greater number of fires during 1989–2010 had lower lantana stem abundance irrespective of distance from streams. In this landscape, total light availability did not affect lantana abundance. Understanding the spatially variable environmental factors in a heterogeneous landscape influencing the distribution of lantana would aid in making informed management decisions at this scale.     

Do Girls Have a Nutritional Disadvantage Compared with Boys? Statistical Models of Breastfeeding and Food Consumption Inequalities among Indian Siblings

Background

India is the only nation where girls have greater risks of under-5 mortality than boys. We test whether female disadvantage in breastfeeding and food allocation accounts for gender disparities in mortality.

Methods and Findings

Secondary, publicly available anonymized and de-identified data were used; no ethics committee review was required. Multivariate regression and Cox models were performed using Round 3 of India’s National Family and Health Survey (2005–2006; response rate = 93.5%). Models were disaggregated by birth order and sibling gender, and adjusted for maternal age, education, and fixed effects, urban residence, household deprivation, and other sociodemographics. Mothers’ reported practices of WHO/UNICEF recommendations for breastfeeding initiation, exclusivity, and total duration (ages 0–59 months), children’s consumption of 24 food items (6–59 months), and child survival (0–59 months) were examined for first- and secondborns (n = 20,395). Girls were breastfed on average for 0.45 months less than boys (95% CI: = 0.15 months to 0.75 months, p = 0.004). There were no gender differences in breastfeeding initiation (OR = 1.04, 95% CI: 0.97 to 1.12) or exclusivity (OR = 1.06, 95% CI: 0.99 to 1.14). Differences in breastfeeding cessation emerged between 12 and 36 months in secondborn females. Compared with boys, girls had lower consumption of fresh milk by 14% (95% CI: 79% to 94%, p = 0.001) and breast milk by 21% (95% CI: 70% to 90%, p<0.000). Each additional month of breastfeeding was associated with a 24% lower risk of mortality (OR = 0.76, 95% CI: 0.73 to 0.79, p<0.000). Girls’ shorter breastfeeding duration accounted for an 11% increased probability of dying before age 5, accounting for about 50% of their survival disadvantage compared with other low-income countries.

Conclusions

Indian girls are breastfed for shorter periods than boys and consume less milk. Future research should investigate the role of additional factors driving India’s female survival disadvantage.     

Modeling the Contributions of Basal Ganglia and Hippocampus to Spatial Navigation Using Reinforcement Learning

A computational neural model that describes the competing roles of Basal Ganglia and Hippocampus in spatial navigation is presented. Model performance is evaluated on a simulated Morris water maze explored by a model rat. Cue-based and place-based navigational strategies, thought to be subserved by the Basal ganglia and Hippocampus respectively, are described. In cue-based navigation, the model rat learns to directly head towards a visible target, while in place-based navigation the target position is represented in terms of spatial context provided by an array of poles placed around the pool. Learning is formulated within the framework of Reinforcement Learning, with the nigrostriatal dopamine signal playing the role of Temporal Difference Error. Navigation inherently involves two apparently contradictory movements: goal oriented movements vs. random, wandering movements. The model hypothesizes that while the goal-directedness is determined by the gradient in Value function, randomness is driven by the complex activity of the SubThalamic Nucleus (STN)-Globus Pallidus externa (GPe) system. Each navigational system is associated with a Critic, prescribing actions that maximize value gradients for the corresponding system. In the integrated system, that incorporates both cue-based and place-based forms of navigation, navigation at a given position is determined by the system whose value function is greater at that position. The proposed model describes the experimental results of [1], a lesion-study that investigates the competition between cue-based and place-based navigational systems. The present study also examines impaired navigational performance under Parkinsonian-like conditions. The integrated navigational system, operated under dopamine-deficient conditions, exhibits increased escape latency as was observed in experimental literature describing MPTP model rats navigating a water maze.     

Serodiagnosis of Tuberculosis in Asian Elephants (Elephas maximus) in Southern India: A Latent Class Analysis

Background

Mycobacterium tuberculosis, a causative agent of chronic tuberculosis disease, is widespread among some animal species too. There is paucity of information on the distribution, prevalence and true disease status of tuberculosis in Asian elephants (Elephas maximus). The aim of this study was to estimate the sensitivity and specificity of serological tests to diagnose M. tuberculosis infection in captive elephants in southern India while simultaneously estimating sero-prevalence.

Methodology/Principal Findings

Health assessment of 600 elephants was carried out and their sera screened with a commercially available rapid serum test. Trunk wash culture of select rapid serum test positive animals yielded no animal positive for M. tuberculosis isolation. Under Indian field conditions where the true disease status is unknown, we used a latent class model to estimate the diagnostic characteristics of an existing (rapid serum test) and new (four in-house ELISA) tests. One hundred and seventy nine sera were randomly selected for screening in the five tests. Diagnostic sensitivities of the four ELISAs were 91.3–97.6% (95% Credible Interval (CI): 74.8–99.9) and diagnostic specificity were 89.6–98.5% (95% CI: 79.4–99.9) based on the model we assumed. We estimate that 53.6% (95% CI: 44.6–62.8) of the samples tested were free from infection with M. tuberculosis and 15.9% (97.5% CI: 9.8 - to 24.0) tested positive on all five tests.

Conclusions/Significance

Our results provide evidence for high prevalence of asymptomatic M. tuberculosis infection in Asian elephants in a captive Indian setting. Further validation of these tests would be important in formulating area-specific effective surveillance and control measures.     

Ultrastructural study of highly enriched follicular dendritic cells reveals their morphology and the periodicity of immune complex binding

Follicular dendritic cells (FDCs) are immune accessory cells found in the follicles of secondary lymphoid organs where they promote B cell maturation in germinal centers (GCs) that develop following antigen exposure. Recently, we published a method for isolating functional murine FDCs in high purity. We reasoned that disruption of FDC reticula in vivo would alter FDC morphology. The present study was undertaken to determine the morphological features of isolated FDCs. FDC-M1 and immune complex (IC) labeling were used to identify FDCs in isolated preparations. Results at the light-microscopic level revealed that isolated FDCs trapped ICs, expressed FDC-M1 and cadherins, but generally appeared non-dendritic. However, at the ultrastructural level, the majority of FDCs exhibited dendrites and typical euchromatic nuclei that appeared as single, bilobed, or double nuclei. Based on morphology, four varieties of FDCs were distinguishable, possibly indicative of differences in maturity. Remarkably, ICs trapped by FDCs showed a distinctive periodic arrangement consistent with that known to induce immune responses by thymus independent-2 (TI-2) antigens that engage and cross-link multiple B cell receptors. The ability of FDCs to trap ICs and then display these T-cell-dependent antigens with repeating periodicity suggests that multiple B cell receptors are cross-linked by antigen on FDCs, thus promoting B cell stimulation and proliferation. Rapid proliferation is characteristic of the GC reaction, and the arrangement of T-dependent antigens in this periodic fashion may help to explain the profuse B cell proliferation in the GC microenvironment. This work was supported by National Institutes of Health Grant AI-17142. Electron microscopy and confocal microscopy were performed at the VCU Department of Neurobiology and Anatomy Microscopy Facility supported, in part, by funding from an NIH-NINDS Center core grant (5P30NS047463).     

Density‐dependence in common tree species in a tropical dry forest in Mudumalai,southern India

Abstract. Density‐dependence in tree population dynamics has seldom been examined in dry tropical forests. Using long‐term data from a large permanent plot, this study examined 16 common species in a dry tropical forest in southern India for density‐dependence. Employing quadrat‐based analyses, correlations of mortality, recruitment and population change with tree densities were examined. Mortality in 1–10 cm diameter trees was largely negatively correlated with conspecific density, whereas mortality in > 10 cm diameter trees was positively correlated. Mortality was, however, largely unaffected by the basal area and abundance of heterospecific trees. Recruitment was poor in most species, but in Lagerstroemia microcarpa (Lythraceae), Tectona grandis (Verbenaceae) and Cassia fistula (Fabaceae), species that recruited well, strong negative correlations of recruitment with conspecific basal area and abundance were found. In a few other species that could be tested, recruitment was again negatively correlated with conspecific density. In Lagerstroemia, recruitment was positively correlated with the basal area and abundance of heterospecific trees, but these correlations were non‐significant in other species. Similarly, although the rates of population change were negatively correlated with conspecific density they were positive when dry‐season ground fires occurred in the plot. Thus, the observed positive density‐dependence in large‐tree mortality and the negative density‐dependence in recruitment in many species were such that could potentially regulate tree populations. However, repeated fires influenced density‐dependence in the rates of population change in a way that could promote a few common species in the tree community.     

Telomerase activity as a measure for monitoring radiocurability of tumor cells.

Radiotherapy plays a key role in the treatment of many tumors. It is difficult to determine what fraction of tumor cells survives after treatment with ionizing radiation. A convenient and sensitive biochemical assay could be efficacious in determining the potential success of radiotherapy. Since telomerase activity is frequently associated with the malignant phenotype, we sought to determine whether a correlation existed between ionizing radiation-induced cell killing and telomerase activity. We evaluated telomerase activity in two telomerase-positive and one telomerase-negative human cell line exposed to ionizing radiation. Telomerase activity was determined using a PCR-based telomeric repeat amplification protocol coupled with ELISA. We found ionizing radiation treatment to decrease the telomerase activity (in plateau phase cells of RKO, HeLa; and growing cells of RKO) in a dose-dependent manner, which correlated with cell death in in vitro tests as well as during tumor regression in nude mice. In contrast, growing HeLa cells after 24 h postradiation treatment showed an increase in telomerase activity, but there was no increase in the levels of mRNA of hTERT. To assess the sensitivity of the telomerase activity assay, we performed mixing experiments of HeLa and AG1522 cell extracts. These studies showed that telomerase activity could be detected in lysate equal to a single HeLa cell when mixed with 10,000 AG1522 cells. Our results indicate that even a few surviving neoplastic cells can be detected by telomerase activity assay. Therefore, detection of telomerase activity may be a useful monitor of radiotherapeutic efficacy and an early predictor of outcome.     

Sunflower Nitrate Reductase: Purification and Characterization

A single isoform, NADH: nitrate reductase (NR), was purified 500 folds from sunflower leaves by affinity chromatography on Blue Sepharose CL-6B. Purified NR had a pH optima of 7.25 and a molecular weight of 210 kD. In SDS-PAGE, two bands of 47 and 56 kD were obtained. NADH: ferric citrate reductase activity was copurified with NR with a specific activity of 2. The Vmax of NADH: ferric citrate reductase was 8.69 units mg^-1 protein and the apparent Km for ferric citrate was 0.435 mM.