A pulse of mid-Pleistocene rift volcanism in Ethiopia at the dawn of modern humans

The Ethiopian Rift Valley hosts the longest record of human co-existence with volcanoes on Earth, however, current understanding of the magnitude and timing of large explosive eruptions in this region is poor. Detailed records of volcanism are essential for interpreting the palaeoenvironments occupied by our hominin ancestors; and also for evaluating the volcanic hazards posed to the 10 million people currently living within this active rift zone. Here we use new geochronological evidence to suggest that a 200 km long segment of rift experienced a major pulse of explosive volcanic activity between 320–170 ka. During this period, at least four distinct volcanic centers underwent large volume (> 10 km3) caldera- forming eruptions and eruptive fluxes were elevated five times above the average eruption rate for the past 700 ka. We propose that such pulses of episodic silicic volcanism would have drastically remodeled landscapes and ecosystems occupied by early hominin populations

Reconstructing the middle to late Pleistocene explosive eruption histories of Popocatépetl, Iztaccíhuatl and Tláloc-Telapón volcanoes in Central México

The Sierra Nevada Volcanic Range (SNVR), which includes Popocat&eacute;petl, Iztacc&iacute;huatl and Tl&aacute;loc-Telap&oacute;n volcanoes, has been the source of multiple large explosive eruptions that have dispersed tephra across central M&eacute;xico. Several eruptions since 40 ka have previously been described, particularly from Popocat&eacute;petl, the southernmost volcano of the range. However, the longer-term eruption history of the SNVR is poorly understood, due to challenges with correlating limited exposures of older pyroclastic sequences, and in discriminating between tephras derived from different sources. Here we describe two extensive exposures located between Popocat&eacute;petl and Iztacc&iacute;huatl volcanoes, which provide a more complete and longer-term explosive eruption record of the SNVR: the Nepopualco and Xalitzintla tephra sequences. A detailed tephrostratigraphic survey, together with new&nbsp;40Ar/39Ar geochronological analyses and glass geochemistry, has permitted the characterization of identified eruption units further leading to the determination of geochemical fields for each volcano and the subsequent discernment of volcanic sources. Our results show that, since the collapse of Los Pies Cone, which destroyed the Paleo-Iztacc&iacute;huatl edifice at 631 &plusmn; 44 ka (2&sigma;), Iztacc&iacute;huatl has produced at least 6 explosive rhyolitic eruptions. After coeval activity with Popocat&eacute;petl, between ~600 and ~ 500 ka, Iztacc&iacute;huatl's explosive activity ceased while Popocat&eacute;petl's continued until present day. Popocat&eacute;petl has produced at least 27 medium to large explosive eruptions (inferred VEI 4&ndash;6), commonly of andesitic to dacitic compositions. Some of these eruptions deposited pumice fallout of &gt;1 m thick in both the Nepopualco and Xalitzintla sequences (e.g. the 339 &plusmn; 16 ka [2&sigma;] NT-23/WRT-7 eruption), suggesting that Popocat&eacute;petl has produced several eruptions similar in magnitude to well-known the ~14 ka Tutti Frutti Pumice (a VEI 6 eruption with a ~ 5 km3&nbsp;tephra volume). The Popocat&eacute;petl and Iztacc&iacute;huatl tephras are interbedded with deposits from more distal volcanoes, including some mafic to intermediate products of unknown sources (possibly from nearby monogenetic cones) and tephras related to the late Pleistocene eruptions of Tl&aacute;loc-Telap&oacute;n (including the tephra layer produced by the San Valentin Ignimbrite, recently&nbsp;40Ar/39Ar dated in this study at ~102 ka; 2&sigma;). Our new chemical, stratigraphic and geochronologic investigations of these pyroclastic deposits, predominantly from Popocat&eacute;petl and Iztacc&iacute;huatl, provide information on the scale and frequency of medium to large magnitude explosive eruptions over a longer-time period than currently known and that have had potential to disperse tephra across central M&eacute;xico since the middle to late Pleistocene. This new data can be used to determine the source of further unknown tephras in the region as well as to better assess the volcanic hazard to the densely populated megalopolis of M&eacute;xico City.</p

Use and cultural significance of Raphia palms

The genus Raphia (Palmae / Arecaceae) contains 22 species and represents a major multiuse resource across tropical Africa and Madagascar. Raphia species provide goods that range from food to construction material and medicine. Its species play a vital cultural role in African societies. Despite its importance, the taxonomy, ecology, and ethnobotany of this genus remain poorly understood. Here, we review the multiplicity of uses, products and cultural importance of Raphia species across its distribution. We provide a near exhaustive list of all products derived from Raphia species, classified by species and major use categories. We record nearly 100 different uses, traded and commercialized at local, regional, and national levels. Most species have several uses. Raphia wine is the most important product, followed by grubs and fiber extraction. Our review improves our understanding of the uses and cultural importance of Raphia species. If Raphia resources are managed responsibly, they will contribute to alleviate poverty, fight against hunger and conserve tropical biodiversity, especially in Africa

Intermediate conductance Ca2+-activated K+ channels modulate human placental trophoblast syncytialization.

Regulation of human placental syncytiotrophoblast renewal by cytotrophoblast migration, aggregation/fusion and differentiation is essential for successful pregnancy. In several tissues, these events are regulated by intermediate conductance Ca2+-activated K+ channels (IKCa), in part through their ability to regulate cell volume. We used cytotrophoblasts in primary culture to test the hypotheses that IKCa participate in the formation of multinucleated syncytiotrophoblast and in syncytiotrophoblast volume homeostasis. Cytotrophoblasts were isolated from normal term placentas and cultured for 66 h. This preparation recreates syncytiotrophoblast formation in vivo, as mononucleate cells (15 h) fuse into multinucleate syncytia (66 h) concomitant with elevated secretion of human chorionic gonadotropin (hCG). Cells were treated with the IKCa inhibitor TRAM-34 (10 µM) or activator DCEBIO (100 µM). Culture medium was collected to measure hCG secretion and cells fixed for immunofluorescence with anti-IKCa and anti-desmoplakin antibodies to assess IKCa expression and multinucleation respectively. K+ channel activity was assessed by measuring 86Rb efflux at 66 h. IKCa immunostaining was evident in nucleus, cytoplasm and surface of mono- and multinucleate cells. DCEBIO increased 86Rb efflux 8.3-fold above control and this was inhibited by TRAM-34 (85%; p<0.0001). Cytotrophoblast multinucleation increased 12-fold (p<0.05) and hCG secretion 20-fold (p<0.05), between 15 and 66 h. Compared to controls, DCEBIO reduced multinucleation by 42% (p<0.05) and hCG secretion by 80% (p<0.05). TRAM-34 alone did not affect cytotrophoblast multinucleation or hCG secretion. Hyposmotic solution increased 86Rb efflux 3.8-fold (p<0.0001). This effect was dependent on extracellular Ca2+, inhibited by TRAM-34 and 100 nM charybdotoxin (85% (p<0.0001) and 43% respectively) but unaffected by 100 nM apamin. In conclusion, IKCa are expressed in cytotrophoblasts and their activation inhibits the formation of multinucleated cells in vitro. IKCa are stimulated by syncytiotrophoblast swelling implicating a role in syncytiotrophoblast volume homeostasis. Inappropriate activation of IKCa in pathophysiological conditions could compromise syncytiotrophoblast turnover and volume homeostasis in pregnancy disease