Changes in landuse alter ant diversity,assemblage composition and dominant functional groups in African savannas

Africa’s savannas are undergoing rapid conversion from rangelands into villages and croplands. Despite limited research, and evidence of deleterious effects to biodiversity, international organisations have earmarked this system for cropland. Invertebrates, and ants in particular, are sensitive indicators of habitat fragmentation, and contribute to ecosystem services at a range of scales. We investigated how rangelands, villages and croplands differ in ant species and functional diversity, and assemblage composition. We sampled ants using pitfall traps at 42 sites (14 replicates each in rangeland, cropland, and village) in northern South African savannas. We investigated the impact of landuse, season, and multiple soil and vegetation habitat variables on ant species diversity, assemblages and functional diversity. Rangelands had the greatest ant species richness, particularly in the wet season. Richness declined with increasing soil clay content. Ant assemblages were distinctly different between landuse types. Rangeland harboured the widest diversity of indicator species, and contained greatest functional diversity. Rangelands accommodated more scavengers, granivores, and plant-matter feeders than cropland, and representation of these groups varied with season. Ants play essential roles in soil nutrient cycling, plant and seedling recruitment, and impact other arthropods through predation and aphidoculous behaviour that in turn influences entire food webs. Thus, the reduced species richness, changes in assemblage composition and the loss of functional groups in ant assemblages found in cropland and villages is potentially problematic. Left unchallenged, these new forms of landuse threaten to characterise the entire African savanna system, impacting not only future ecological, but possibly also human wellbeing.     

Seasonal variation in avian diversity and tolerance by migratory forest specialists of the patch-isolation gradient across a fragmented forest system

Forest-habitat loss and fragmentation reduce connectivity, presenting dispersal challenges for many forest-dependent species with deleterious effects on community structure and diversity. It is expected that avian forest specialists are vulnerable to fragmentation, yet seasonal migrants may be more resilient to isolation effects than sedentary specialists. We surveyed bird communities in 138 habitat patches of the critically endangered Indian Ocean Coastal Belt, South Africa, across a range of isolation distances from mainland forests during the breeding and non-breeding seasons. We quantified taxonomic and functional diversity per patch based on species’ traits and performed 26 generalized linear mixed-effects models on the effects of isolation and the amount of habitat in the surrounding matrix on avian trait-diversity measurements. We compared diversity measures between seasons for evidence of resilience to isolation effects for migrants and compared linear regressions of isolation-distance effects to segmented regressions at various isolation distances to explore dispersal limits of sedentary forest specialists. All avian diversity measures were higher during the breeding season. The amount of surrounding habitat was a positive driver of all diversity measures. Isolation-distance effects had the most negative effect during the breeding season, and on sedentary forest specialists, which were unable to disperse across isolation distances > 500 m. Sedentary forest specialists are a conservation priority given (a) their value in perpetuating ecosystem services and (b) their vulnerability to isolation effects. Migratory forest specialists exhibited resilience to the isolation effect during non-breeding; thus, certain specialized niches may be occupied given the vagility of migratory forest specialists.     

The role of resveratrol on skeletal muscle cell differentiation and myotube hypertrophy during glucose restriction

Considering the well-known antioxidant properties of statins, it seems important to assess their impact on major markers of oxidative stress (superoxide anion radical, nitric oxide, and index of lipid peroxidation) to compare the antioxidative potentials of atorvastatin and simvastatin during the different degrees of hyperhomocysteinemia (HHcy) in rats. This study was conducted on adult male Wistar albino rats (n = 90; 4 weeks old; 100 ± 15 g body mass) in which HHcy was achieved by dietary manipulation. For 4 weeks, the animals were fed with one of the following diets: standard rodent chow, diet enriched in methionine with no deficiency in B vitamins (folic acid, B6, and B12), or diet enriched in methionine and deficient in B vitamins (folic acid, B6, and B12). At the same time, animals were treated with atorvastatin at doses of 3 mg/kg/day i.p. or simvastatin at doses of 5 mg/kg/day i.p. Levels of superoxide anion radical and TBARS were significantly decreased by administration of simvastatin in normal and high-homocysteine (Hcy) groups (p < 0.05). At 4 weeks after feeding with purified diets, the concentrations of the GSH, CAT, and SOD antioxidants were significantly affected among all groups (p < 0.05). Our results indicated that statin therapy had variable effects on the redox status in hyperhomocysteinemic rats, and simvastatin demonstrated stronger antioxidant effects than did atorvastatin.     

Diverse Legionella‐Like Bacteria Associated with Testate Amoebae of the Genus Arcella (Arcellinida: Amoebozoa)

Diverse species of Legionella and Legionella‐like amoebal pathogens (LLAPs) have been identified as intracellular bacteria in many amoeboid protists. There are, however, other amoeboid groups such as testate amoeba for which we know little about their potential to host such bacteria. In this study, we assessed the occurrence and diversity of Legionella spp. in cultures and environmental isolates of freshwater arcellinid testate amoebae species, Arcella hemispherica, Arcella intermedia, and Arcella vulgaris, via 16S rRNA gene sequence analyses and fluorescent in situ hybridization (FISH). Analysis of the 16S rRNA gene sequences indicated that A. hemispherica, A. intermedia, and A. vulgaris host Legionella‐like bacteria with 94–98% identity to other Legionella spp. based on NCBI BLAST search. Phylogenetic analysis placed Legionella‐like Arcella‐associated bacteria (LLAB) in three different clusters within a tree containing all other members of Legionella and LLAPs. The intracellular localization of the Legionella within Arcella hosts was confirmed using FISH with a Legionella‐specific probe. This study demonstrates that the host range of Legionella and Legionella‐like bacteria in the Amoebozoa extends beyond members of “naked” amoebae species, with members of the testate amoebae potentially serving an ecological role in the dispersal, protection, and replication of Legionella spp. in natural environments.     

Landuse Change in Savannas Disproportionately Reduces Functional Diversity of Invertebrate Predators at the Highest Trophic Levels: Spiders as an Example

Predators play a disproportionately positive role in ensuring integrity of food webs, influencing ecological processes and services upon which humans rely. Predators tend to be amongst the first species to be affected by anthropogenic disturbance, however. Spiders impact invertebrate population dynamics and stabilise food webs in natural and agricultural systems (potentially mitigating against crop pests and reduced yields). Africa’s savannas are undergoing continent-wide conversion from low-density rangelands to villages and croplands, as human populations burgeon. Despite limited research, and evidence of deleterious impacts to biodiversity, African savannas are earmarked by prominent international organisations for conversion to cropland. Given the key role of spiders in food webs, they can have beneficial impacts in agroecosystems. Furthermore, functional diversity (FD) reflects ecosystem pattern and processes better than species diversity, so we evaluated impacts of large-scale landuse change on both species richness and FD. We surveyed spiders using pitfall traps at 42 sites (14 replicates each in rangeland, cropland, and villages) in South African savannas, investigating effects of landuse, season, and habitat variables on spider species diversity and FD. Species richness was lowest in villages. FD was lowest in cropland, however, with reduced representation of traits associated with hunting of larger invertebrates. Furthermore, there were fewer specialists in croplands. These findings suggest that even when cropland does not impact species diversity, loss of FD can still occur. As savanna systems transform, impacts on invertebrate population dynamics may increase the possibility of a breakdown in pest control in natural and agricultural systems, given changes in FD of invertebrate predators.     

A bicistronic transgene system for genetic modification of <Emphasis Type="Italic">Parthenium argentatum</Emphasis>

Parthenium argentatum (guayule) was transformed with a bicistronic transgene containing a viral 2A cleavage sequence. The transgene includes the coding sequences of two key enzymes of the mevalonate pathway, 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) and farnesyl pyrophosphate synthase (FPPS), involved in rubber biosynthesis. The viral 2A peptide sequence located between the two transgenes allowed for their co-expression via the Arabidopsis CBF2 (C-Binding repeat Factor 2) cold-inducible promoter. We identified three independent transgenic lines expressing the bicistronic transgenes upon cold treatment and examined the rubber content in the in vitro guayule plants.     

Drought-avoidant soybean germplasm maintains nitrogen-fixation capacity under water stress

Inoculated soybeans (Glycine max L. (Merrill)) were grown in controlled environments to evaluate the relationship between genotype and plant water status on nodule function, nitrogen assimilation, growth rates, and seed yield. Plants were grown under well-watered (WW) and water-stressed (WS) conditions during the linear pod-filling growth stage in sand culture using N-free nutrient solution. Dry matter and N accumulation were greater for the drought-adapted Plant Introduction 416937 (PI) than for Forrest, a commercially adapted genotype of similar phenology. These differences are attributed to: (i) more favorable internal water balance throughout the pod-filling period (higher total leaf water potential), (ii) higher photosynthetic function (more total leaf area and higher net carbon exchange rates), and (iii) stronger nodule function (larger nodule mass, greater specific and total nodule activity, and thus more nitrogen assimilation) for the PI than for Forrest. While Forrest out yielded the PI under WW conditions, the percentage reduction in seed mass per plant was less for the PI than for Forrest when both genotypes were exposed to desiccating conditions. The inference is that soybean germplasm with the capacity to maintain tissue turgidity, and thus leaf and nodule function, during reproductively-imposed desiccation may reduce the extent to which yield is compromised during drought. These findings have implications for the role of symbiotic nitrogen fixation in conserving yield under dry weather conditions.Abbreviations DAE Days After Emergence - NCE Net CO₂ Exchange - PI PI 416937 - SNA Specific Nodule Activity - TNA Total Nodule Activity - WS Water Stressed - WW Well Watered