Climate–growth relationships of tropical tree species in West Africa and their potential for climate reconstruction

Most tropical regions are facing historical difficulties of generating biologically reconstructed long‐term climate records. Dendrochronology (tree‐ring studies) is a powerful tool to develop high‐resolution and exactly dated proxies for climate reconstruction. Owing to the seasonal variation in rainfall we expected the formation of annual tree rings in the wood of tropical West African tree species. In the central‐western part of Benin (upper Ouémé catchment, UOC) and in northeastern Ivory Coast (Comoé National Park, CNP) we investigated the relationship between climate (precipitation, sea surface temperature (SST)) and tree rings and show their potential for climate reconstruction. Wood samples of almost 200 trees belonging to six species in the UOC and CNP served to develop climate‐sensitive ring‐width chronologies using standard dendrochronological techniques. The relationship between local precipitation, monthly SST anomalies in the Gulf of Guinea, El Niño‐ Southern Oscillation (ENSO) and ring‐width indices was performed by simple regression analyses, two sample tests and cross‐spectral analysis. A low‐pass filter was used to highlight the decadal variability in rainfall of the UOC site. All tree species showed significant relationships with annual precipitation proving the existence of annual tree rings. ENSO signals could not be detected in the ring‐width patterns. For legume tree species at the UOC site significant relationships could be found between SST anomalies in the Gulf of Guinea indicating correlations at periods of 5.1–4.1 and 2.3 years. Our findings accurately show the relationship between tree growth, local precipitation and SST anomalies in the Gulf of Guinea possibly associated with worldwide SST patterns. A master chronology enabled the reconstruction of the annual precipitation in the UOC to the year 1840. Time series analysis suggest increasing arid conditions during the last 160 years which may have large impacts on the hydrological cycles and consequently on the ecosystem dynamics and the development of socio‐economic cultures and sectors in the Guinea‐Congolian/Sudanian region.     

Culex torrentium mosquitoes from Germany are negative for Wolbachia

Wolbachia (Rickettsiales: Anaplasmataceae) infects a wide range of arthropods, including several mosquito species. The bacterium is known to induce a plethora of phenotypes in its host, examples being the reproductive phenotype cytoplasmic incompatibility or resistance against infection with arboviruses. The latter is especially relevant when assessing the vector competence of mosquito species for emerging arboviruses. Thus, knowledge of Wolbachia infection status is important for the assessment of vector competence. To facilitate Wolbachia screening in mosquito populations, a quantitative polymerase chain reaction (qPCR) assay was developed to enable high‐throughput analysis of mosquito samples. Using this assay, the Wolbachia infection status of the two most common Culex mosquito species in Germany, Culex pipiens biotype pipiens Linnaeus (Diptera: Culicidae) and Culex torrentium Martini (Diptera: Culicidae), was assessed. About 93% of all tested C. pipiens biotype pipiens individuals were positive for Wolbachia, whereas none of the C. torrentium samples was found to be infected. Furthermore, other applications of the qPCR assay were explored by assessing a potential link between the levels of Wolbachia and West Nile virus (WNV) infections in German C. pipiens biotype pipiens mosquitoes. No relationship was found between the two variables, indicating that a Wolbachia‐induced antiviral phenotype in this mosquito population is not exclusively attributable to the general level of bacterial infection.     

Molecular phylogeny of treecreepers (Certhia) detects hidden diversity†

We sequenced a part of the mitochondrial cytochrome-b gene from the seven treecreeper species, including 18 subspecies, to reconstruct the phylogeny of the genus Certhia . Species status of all seven species could be affirmed. Certhia discolor , C. himalayana , C . nipalensis , and C . tianquanensis , the species with relatively small distribution ranges in southeast Asia and simple territorial song, are found at the base of all phylogenetic trees, although without good support. A comparatively recent sister species of C. tianquanensis is C. nipalensis , replacing C. discolor as closest relative. Certhia familiaris , C. brachydactyla and C. americana form a derived set of species (again only weak support). The closest relative of C. americana is C. brachydactyla . The C. familiaris subtree is deeply split into two well-defined population groups: a Eurasian group including populations in northern China (Qinling range northward and all Eurasia) and a Sino-Himalayan group (Himalayas and China excluding northern China). In accordance with acoustic characters, the three subspecies hodgsoni , mandellii and khamensis of the Sino-Himalayan group are combined and elevated to species rank: Certhia hodgsoni . Certhia discolor manipurensis is deeply split from nominate discolor as well, and is also promoted to species level. Within C. brachydactyla (western palearctic) and within C. hodgsoni (Himalayas, China) several populations form well-supported separate lineages that diverged quite recently and represent subspecies level. In all other species, molecular–genetic and vocal characters support traditional species delimitation.     

Bromeliads provide shelter against fire to mutualistic spiders in a fire‐prone landscape

1. A key challenge in the study of mutualistic interactions is understanding sources of variation that strengthen or weaken these interactions. In spider–plant mutualisms, spiders benefit plants by improving plant nutrition and protecting plants from herbivory. Although the benefits of plants to spider growth and survival are often claimed, they are rarely demonstrated. 2. In this study, empirical evidence is provided that bromeliads (Bromelia balansae, Bromeliaceae) are essential for the resilience of the mutualistic bromeliad‐living jumping spider populations (Psecas chapoda, Salticidae) after a fire event, sheltering spiders from the heat of the flames. 3. Spider populations were compared before and after a natural fire event and it was shown that spiders of different ages survived the fire. The survival of such individuals allowed the population of P. chapoda spiders to recover rapidly, returning to pre‐fire levels in 5 months. 4. Bromeliads reduced the susceptibility of P. chapoda spiders to burning, and this mutualistic relationship contributed to the resilience of the spider population after a fire event. It is suggested that frequent fires in fire‐prone landscapes may have strengthened this spider–plant relationship, contributing to the maintenance and evolution of this association.     

Metabolite Concentrations and Phase Relations in d-Fructose Induced Glycolytic Oscillations

The frequency of glycolytic oscillations in yeast cells is only slightly modified by the consumption rate of either glucose or fructose, but it is reduced to 1 /2 to 2/3 if the ketohexose is the only substrate. Phase relations between NADH, adenine nucleotides and sugar phosphates (G-6-P, F-6-P, FDP, DAP) are independent of the hexose fermented. With fructose as a substrate the amplitudes of adenylates and hexose phosphates are distinctly smaller than with glucose. The maximum of G-6-P is higher with glucose and the minimum concentration of FDP is higher with fructose. In the transition to anaerobiosis FDP, adenosine 5′-diphosphate and adenosine 5′-phosphate are extremely high, whereas G-6-P, F-6-P and ATP concentrations are lower if fructose is the substrate fermented. The results are indicative for different control characteristics of the phosphofructokinase step, but on their basis it cannot be distinguished between a direct interaction of fructose (or one of its derivatives) on the phosphofructokinase kinetics or the existence of a bypass for fructose which might be able to withdraw a part of the substrate from the control point at the phosphofructokinase.