Stereochemical course of the hydroboration of highly hindered steroidal olefins. A ready synthesis of 14 beta- and 8 alpha,14 beta-steroids

Hydroboration of 5 alpha-cholest-8-ene, 5 alpha,14 beta-cholest-8-ene and 5 alpha,14 beta-cholest-7-ene provides a simple route to oxygenated steroids with 14 beta- and 8 alpha,14 beta- unnatural stereochemistry.     

Synthesis of 7 alpha,12 alpha-dihydroxy-3 alpha- [2-(beta-D-glucopyranosyl)acetyl]-5 beta-cholan-24-oic acid

A C-glucoside of cholic acid was synthesized by the introduction of an acetyl group at position 3 alpha and direct one-pot C-glucosidation using 2,3,4,6-tetra-O-benzyl-alpha-D-glucopyranosyl chloride.     

Metabarcoding reveals seasonal and spatial patterns of arthropod community assemblages in two contrasting habitats: Desert and oasis of the Baja California Peninsula,Mexico

Aim

Desert springs or oases are the only permanent mesic environments in highly water-limited arid regions. Oases have immense cultural, evolutionary and ecological importance for people and a high number of endemic and relic species. Nevertheless, they are also highly vulnerable ecosystems, with invasive species, overexploitation and climate change being the primary threats. We used the arthropod communities' spatiotemporal diversity and distribution patterns as a proxy to understand biodiversity dynamics in two geographically close but ecologically contrasting and highly threatened ecosystems: deserts and oases.

Location

Baja California Peninsula, Mexico.

Methods

Arthropod communities at five oases and surrounding desert scrub areas were sampled in two seasons. Using DNA metabarcoding and traditional taxonomic surveys, we tried to identify what biotic and abiotic characteristics of the habitat are important drivers of arthropod diversity and how these characteristics can change across spatial and temporal scales.

Results

Over 6200 individuals representing 23 orders were collected. In oasis samples, the community composition fluctuated more in space (i.e. among sites) than in time (i.e. seasons). Thus, seasonal changes did not affect oasis community diversity and composition, but the dissimilarity among sites increased with geographic distance. Moreover, anthropic activities negatively correlated with arthropod diversity in oases. On the other hand, the season, geography (e.g. latitude) and biotic characteristics of the habitat (e.g. sampled scrub species) significantly affected the diversity and composition of the desert arthropod communities.

Main Conclusions

Neutral dynamics (e.g. historical climatic events, dispersal limitation and spatial component) and human impact significantly influenced the biodiversity patterns of each oasis. In contrast, the habitat's seasonal variation and biotic characteristics were the most important variables influencing the diversity of the desert communities. Baja California oases harbour distinct invertebrate communities; therefore, each oasis should be conserved individually to preserve these unique assemblages.     

The distance dependence prediction of the Janzen-Connell hypothesis: a meta-analysis

The Janzen-Connell hypothesis explains the maintenance of tropical diversity through the interacting effects of parent-centered dispersal patterns and distance- and density-dependent propagule survival. These effects were thought to support regular spacing of species within tropical forest, enhancing diversity. One of the predictions of the hypothesis is that seed and seedling survival should improve with increased parental distance. Although there are many independent tests of this hypothesis for individual species, there are few synthetic studies that have brought these data together to test its validity across species. This paper reports the results of a meta-analysis of the effect of distance on enhancing propagule survival, employing an odds-ratio effect size metric. We found no general support for the distance-dependent prediction of the hypothesis, and conclude that further testing to explore this hypothesis as a diversity-maintaining mechanism is unnecessary. However, we did find that distance from parent slightly reduces survivorship in the temperate zone, as contrasted with the tropics, and we saw stronger evidence in support of the hypothesis for seedlings than for seeds. The phenomenon of enhanced propagule survival with distance from the parent may be important for the population biology of particular species, but it is not a general phenomenon across communities, life history stages or life forms.     

Impaired chloroplast positioning affects photosynthetic capacity and regulation of the central carbohydrate metabolism during cold acclimation

Photosynthesis Research - Photosynthesis and carbohydrate metabolism of higher plants need to be tightly regulated to prevent tissue damage during environmental changes. The intracellular position...     

Mitochondrial Disorders in Alzheimer’s Disease

Biochemistry (Moscow) - Alzheimer’s disease is the most common age-related neurodegenerative disease. Understanding of its etiology and pathogenesis is constantly expanding. Thus, the...     

Lamin A as a Determinant of Mechanical Properties of the Cell Nucleus in Health and Disease

Biochemistry (Moscow) - One of the main factors associated with worse prognosis in oncology is metastasis, which is based on the ability of tumor cells to migrate from the primary source and to...