Health effects in fish from the polluted Orlando Dam and Klipspruit wetland system,Soweto, South Africa

Pollution of aquatic ecosystems often results in adverse environmental disturbances, including physiological and/ or histomorphological changes in fish. The health of Clarias gariepinus sampled from two polluted water bodies, Orlando Dam and a pond in the Klipspruit wetland catchment, Soweto, was investigated in 2015–2016. Limited fish health-related data is available for this highly impacted freshwater ecosystem. Fish were collected between April 2015 and February 2016. A necropsy and a histological assessment were done on various target organs of each fish. Water and sediment samples were analysed for selected organic and inorganic compounds. Macroscopic assessment revealed abnormally shaped urogenital papillae, morphological alterations of the gonads, as well as discoloration of liver tissue. These observations were supported by microscopic evidence of hepatic histological alterations in fish from Orlando Dam, as well as the presence of both female and male gonadal tissue (intersex) in 13.6% and 50% of fish from the wetland pond and the Orlando Dam, respectively. Water analyses showed high levels of faecal coliform bacteria and metal concentrations and sediment analyses showed detectable levels of potential endocrine disrupting chemicals.     

A response to: Limitations within "The Limits to Tree Height"

Here we respond to the communication in American Journal of Botany (96: 542-544 in this issue) by Netting, who proposes several ways in which our paper "The Limits to Tree Height" (Nature 428: 851-854) may have erred in estimating the biophysical limits to height growth in Sequoia sempervirens. We first explain that because embolism repair requires long time periods and is generally incomplete, xylem vulnerability characteristics offer a sound basis for estimating performance limits in woody plants. We reaffirm our earlier use of vertical gradients of foliar carbon isotope composition with new data for S. sempervirens. We support these arguments with reference to studies in other tree species. We take exception with Netting's view that the turgor pressure-cell expansion relationship for Zea mays is applicable to S. sempervirens. Finally, we second Netting's call for more work on carbon allocation vis a vis height growth limits.     

Identification and expression analysis of microRNAs and targets in the biofuel crop sugarcane

Background  

MicroRNAs (miRNAs) are small regulatory RNAs, some of which are conserved in diverse plant genomes. Therefore, computational identification and further experimental validation of miRNAs from non-model organisms is both feasible and instrumental for addressing miRNA-based gene regulation and evolution. Sugarcane (Saccharum spp.) is an important biofuel crop with publicly available expressed sequence tag and genomic survey sequence databases, but little is known about miRNAs and their targets in this highly polyploid species.     

Effects of bird predation on arthropod abundance and tree growth across an elevational gradient

Considerable uncertainty surrounds the conditions under which birds can cause trophic cascades. In a three‐year experiment, we studied the direct and indirect effects of insectivorous birds on arthropod abundance, herbivory, and growth of striped maple Acer pensylvanicum saplings in a northern hardwood forest of central New Hampshire, USA. We manipulated bird predation by erecting exclosures around saplings and directly manipulated herbivory by removing herbivores. We also examined how climate modifies these interactions by replicating the experiment at three locations along an elevational gradient. Effects of bird predation were variable. Overall, mean arthropod biomass was 20% greater on saplings within bird exclosures than on controls (p<0.05). The mean biomass of leaf‐chewing herbivores, primarily Lepidoptera larvae, was 25% greater within exclosures but not statistically different from controls. To a lesser degree, mean herbivore damage to foliage within exclosures exceeded that of controls but differences were not significant. We also did not detect significant treatment effects on sapling shoot growth. The high understory vegetation density relative to bird abundance, and low rate of herbivory during the study (mean 5% leaf area removed, controls), may have limited the ability of birds to affect sapling growth. Climate effects operated at multiple scales, resulting in a complex interplay of interactions within the food web. Regional synchrony of climatic conditions resulted in annual fluctuations in herbivore abundance and tree growth that were shared across elevations. At the same time, local environmental variation resulted in site differences in the plant, herbivore, and bird communities. These patterns resulted in a mosaic of top–down strengths across time and space, suggesting an overall pattern of limited effects of birds on plant growth, possibly interspersed with hotspots of trophic cascades.     

Frequency and clinical patterns of stroke in Iran - Systematic and critical review

Background  

Cerebrovascular disease is the second commonest cause of death, and over a third of stroke deaths occur in developing countries. To fulfil the current gap on data, this systematic review is focused on the frequency of stroke, risk factors, stroke types and mortality in Iran.