Environments In Tropical Regions Research Articles

Mixta mediterraneensis as a novel and abundant gut symbiont of the allergen-producing domestic mite Blomia tropicalis

Blomia tropicalis is an allergen-producing mite in the human environment in tropical regions. The microbiome of B. tropicalis was described using the barcode sequencing region of V4 16S rDNA and genome assemblage. Mixta mediterraneensis, previously isolated from human skin swabs, was identified as a B. tropicalis gut symbiont based on genome assembly. The microbiome contains two bacteria, Staphylococcus and M. mediterraneensis. The number of M. mediterraneensis 16S DNA copies was 106 per mite and 109 per feces in the rearing chamber based on qPCR quantification. The profile of this bacterium reached 50% of reads in the mite gut and feces. Genomic analyses revealed that the bacterium has several metabolic pathways that suggest metabolic cooperation with the mite host in vitamin and amino acid synthesis, nitrogen recycling, and antimicrobial defense. Lysozyme is present in the symbiotic bacterium but absent in the mite. The B. tropicalis microbiome contained Staphylococcus, which accelerates mite population growth. Mites can digest Staphylococcus by using specific enzymes with hydrolytic functions against bacterial cell walls (chitinases and cathepsin D), leading to endocytosis of bacteria and their degradation in lysosomes and phagosomes. Gene expression analysis of B. tropicalis indicated that phagocytosis was mediated by the PI3-kinase/Akt pathway interacting with the invasins produced by M. mediterraneensis. Moreover, the symbiont had metabolic pathways that allowed it to recycle the mite metabolic waste product guanine, known as a mite attractant. The mite host symbiont enhances mite aggregation in the feces, and the fecal–oral transmission route is excepted.

Root Adaptation via Common Genetic Factors Conditioning Tolerance to Multiple Stresses for Crops Cultivated on Acidic Tropical Soils.

Crop tolerance to multiple abiotic stresses has long been pursued as a Holy Grail in plant breeding efforts that target crop adaptation to tropical soils. On tropical, acidic soils, aluminum (Al) toxicity, low phosphorus (P) availability and drought stress are the major limitations to yield stability. Molecular breeding based on a small suite of pleiotropic genes, particularly those with moderate to major phenotypic effects, could help circumvent the need for complex breeding designs and large population sizes aimed at selecting transgressive progeny accumulating favorable alleles controlling polygenic traits. The underlying question is twofold: do common tolerance mechanisms to Al toxicity, P deficiency and drought exist? And if they do, will they be useful in a plant breeding program that targets stress-prone environments. The selective environments in tropical regions are such that multiple, co-existing regulatory networks may drive the fixation of either distinctly different or a smaller number of pleiotropic abiotic stress tolerance genes. Recent studies suggest that genes contributing to crop adaptation to acidic soils, such as the major Arabidopsis Al tolerance protein, AtALMT1, which encodes an aluminum-activated root malate transporter, may influence both Al tolerance and P acquisition via changes in root system morphology and architecture. However, trans-acting elements such as transcription factors (TFs) may be the best option for pleiotropic control of multiple abiotic stress genes, due to their small and often multiple binding sequences in the genome. One such example is the C2H2-type zinc finger, AtSTOP1, which is a transcriptional regulator of a number of Arabidopsis Al tolerance genes, including AtMATE and AtALMT1, and has been shown to activate AtALMT1, not only in response to Al but also low soil P. The large WRKY family of transcription factors are also known to affect a broad spectrum of phenotypes, some of which are related to acidic soil abiotic stress responses. Hence, we focus here on signaling proteins such as TFs and protein kinases to identify, from the literature, evidence for unifying regulatory networks controlling Al tolerance, P efficiency and, also possibly drought tolerance. Particular emphasis will be given to modification of root system morphology and architecture, which could be an important physiological “hub” leading to crop adaptation to multiple soil-based abiotic stress factors.

Seasonal Differences of Psychological and Physiological Responses in Tropical Urban Climate

This research aims to use the outdoor thermal environment evaluation index ETFe to quantify effects on the thermal sense of the human body of a tropical region climate with small annual temperature differences, and to examine seasonal differences in the thermal sense. Given that the average temperature of the earth is forecasted to rise, studying the effects on the human body from outdoor thermal environments in tropical regions is important for considering how to spend time outdoors in the future. This study clarifies seasonal differences in effects on the human body by comparing the effects on the thermal sensations of the human body from outdoor thermal environments in the winter and the dry season of Bangkok, Thailand in the tropics. The mobile measurements were carried out on the campus of Chulalongkorn University, Bangkok, Thailand. The subjects reported the thermal sensation and the thermal comfort that they experienced while exposed at the observation point. Air temperature, humidity, air velocity, short-wave solar radiation, long-wave thermal radiation, ground surface temperature, sky factor and the ratio of green and water surface solid angles were measured. We found no large seasonal difference between the winter and the dry season in skin temperature due to body temperature regulation. It is clear that in the winter season, people prefer a lower temperature than in the dry season, and in the dry season they tolerate higher temperatures than in winter. The effect of the seasonal difference appears in the amount of change to thermal sensation. We found that it is difficult for seasonal differences to greatly affect the amount of change to thermal comfort. We found that the effect of seasonal difference is that people show stronger responses to thermal comfort for thermal sensation in winter than in the dry season.

LesleyaLesquereux from the Pennsylvanian of the Iberian Massif: part of a dryland megaflora from the Variscan orogen, northwestern Portugal

The Carboniferous – early Permian plant genus Lesleya is a characteristic component of “dryland floras” that occupied a wide range of moisture-stressed, well-drained environments in tropical regions of Euramerica. Fossil records of Lesleya are almost exclusively found in basinal lowlands. For example, occurrences in Early Pennsylvanian-age, seasonally dry, parautochthonous deposits in basinal lowlands of North America (e.g., Illinois Basin, USA) indicate that Lesleya lived in that region in low-altitude (lowland) paleoenvironments during dry climatic intervals. In this paper, we document the first occurrence of Lesleya during the Carboniferous on the Iberian Massif, in lower Gzhelian (Upper Pennsylvanian) strata of the Douro Carboniferous Basin, in northwestern Portugal. This newly discovered occurrence includes a new species, Lesleya iberiensis sp. nov., recognized on the basis of natural molds of leaves. The Portuguese Lesleya fossils are from upland intramontane deposits and occur between coal beds. Their fossil remains are preserved in mica-rich shales that were deposited between sandstone-dominated fluvial and shale-dominated lacustrine deposits, suggesting that this megaflora was deposited near freshwater bodies. These new data provide evidence that this megaflora grew in mountain riparian environments within the Variscan orogen, either in localized, well-drained areas or during drier climatic intervals in the Late Pennsylvanian.

Early Palaeozoic palaeobiogeography and palaeoecology of stylophoran echinoderms

Stylophorans (cornutes, mitrates) represent one of the most diverse classes of Cambro-Ordovician echinoderms. They were free-living, benthic, non-radiate forms, closely related to asterozoans and crinoids. Taphonomic, sedimentological, and palaeosynecological data provide useful information on key aspects of stylophoran palaeoecology. Such a combined approach suggests that the rarity of stylophorans in proximal environments (above storm-wave base) was probably original and does not exclusively result from the possession of a loosely articulated polyplated calcitic test. Conversely, stylophorans were relatively abundant in deeper settings (below storm-wave base), where they frequently occur in low-diversity dense beds (several tens to hundreds of individuals per square metre). Such assemblages were either largely dominated by stylophorans only (Middle Cambrian–Darriwilian), or by the association of both stylophorans and ophiuroids (latest Darriwilian–Silurian). Comparison with ecological requirements of similar modern and fossil dense populations of ophiuroids suggests that stylophoran beds occurred in well-oxygenated, oligotrophic waters with low predatory pressure, and that sea temperature played a key role in the palaeobiogeographic distribution of stylophorans. Seven main stylophoran biofacies are identified and described. The associated environments and tropical distribution of primitive, heavily-plated forms suggest that the initial radiation of the class probably took place in warm to temperate shallow settings (earliest Middle Cambrian–Late Cambrian). However, from this primitive stock, stylophorans radiated several times towards deeper and/or colder environments, possibly because of the lower predation pressure in such settings (“cothurnocystid” cornutes in the Middle Cambrian, mitrates in the Late Cambrian, hanusiids in the Tremadocian). As a consequence, the fact that most Cambro-Ordovician cornutes and mitrates were “psychrospheric” (i.e. cold-water adapted) probably explains their relatively wide palaeobiogeographic distribution. In high palaeolatitudes, Cambro-Ordovician stylophorans were abundant and diverse in shallow to deep environments, but they were generally restricted to deep settings in low palaeolatitudes. The great Caradocian transgression favoured the extension of stylophorans from circum-polar regions (e.g. western margin of Gondwana) towards external settings at lower palaeolatitudes (Avalonia, Baltica, and eastern margin of Laurentia), where one group of mitrates underwent a major radiation (anomalocystitids), and extended towards shallower (and warmer) palaeoenvironments. In contrast, all Silurian stylophoran assemblages known so far are rare, poorly diversified, and restricted to shallow, warm to temperate environments in tropical regions. This distribution partly results from (1) the probable eradication of psychrospheric forms (e.g. cornutes) because of the prolonged anoxia of deep environments in the late Hirnantian–early Silurian of West Gondwana, (2) the radiation of some mitrates (anomalocystitids) in shallow tropical settings in the late Ordovician, and (3) of strong taphonomic and/or sampling biases (numerous ghost lineages).

The Longevity of Seeds

INTRODUCTION Ewart (1908) and Harrington (1972) provided summary lists of species with seeds that were short-lived, survived for moderately long periods, or survived for very long periods. Time is only one of several variables of concern, however; seed longevity is influenced markedly by the storage environment. Ambient environments in tropical regions are generally poorer for seed storage than those of temperate regions, and so the maintenance of viability during storage is generally a greater problem in tropical regions. However, there is no need to distinguish among crop species with regard to region of production or origin when considering the physiology of seed survival. The major difference transcends these areas; it is a consequence of different responses to desiccation. Roberts (1973) classified species into two categories with regard to seed storage behavior: orthodox and recalcitrant. Orthodox seeds tolerate considerable desiccation, and storage longevity is greatly increased thereby (Roberts, 1973). Similarly, considerable increase in orthodox seed longevity results from reduction in storage temperature, particularly since the seeds can be stored at subzero temperatures once they have been dried to a sufficiently low moisture content. These aspects of the physiology of orthodox seeds provide seedsmen with considerable scope to enhance storage life by environmental modification. If these responses are quantified, then the benefits to seed longevity can be assessed against the costs of modifying seed storage environments. In contrast, recalcitrant seeds do not survive desiccation (Roberts, 1973; Chin, 1988). In addition, the storage temperature cannot be reduced greatly because very moist seeds are damaged by cooling to subzero (and in some cases higher) temperatures. Thus, the scope for modifying seed storage environment is limited, and so it is difficult to improve the storage life of recalcitrant seeds beyond comparatively short periods (Ring and Roberts, 1979; Roberts et al., 1984). Fortunately, most crops have orthodox seeds (Ring and Roberts, 1979; Roberts, 1973; Roberts et al., 1984), including most