Thermolimit respirometry: an objective assessment of critical thermal maxima in two sympatric desert harvester ants, Pogonomyrmex rugosus and P. californicus.
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The critical thermal maxima (CT(max)) of two sympatric, diurnal, thermophilic harvester ants from the Mojave Desert, USA (Pogonomyrmex rugosus and P. californicus) were measured by ramping their temperature upwards at a rate of 0.25 degrees C min(-1) during flow-through respirometry with optical activity detection. Rates of CO(2) emission ((CO(2))) increased exponentially to plateau values that were twice as high in P. californicus as P. rugosus on a mass-specific basis. (CO(2)) then fell sharply, during which gross motor activity (measured optically) and spiracular control (measured from (CO(2)) variation) abruptly ceased, yielding two independent measures of CT(max). As determined by loss of muscular coordination, the CT(max) of Pogonomyrmex rugosus was 51.57+/-0.38 degrees C (mean +/- S.D., while that of Pogonomyrmex californicus was 51.74+/-0.25 degrees C. As determined by loss of spiracular control, the CT(max) of Pogonomyrmex rugosus was 51.59+/-0.35 degrees C, while that of Pogonomyrmex californicus was 51.78+/-0.37 degrees C. In each species a pronounced post-mortal peak of (CO(2)) was observed. The major ecological and behavioral differences of the two species are not reflected in their CT(max) values, which do not differ significantly. 'Thermolimit respirometry' allows CT(max) to be estimated objectively with coefficients of variation (S.D./mean) <1%, lending confidence to comparisons between species or treatment groups. (+info)
Identification of ergonomic issues that affect workers in oilrigs in desert environments.
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The main objective of this research was to conduct an assessment of ergonomic-related problems in oilrigs in a desert environment. A checklist, physical audit and medical records were used in the investigation. The results showed significant health, environment and work-related problems that could be attributed to ergonomic deficiencies in the work system of the oilrig. Some major ergonomic issues identified were hard physical work, back pain, discomfort, hot environment, long shift, and diverse schedule. Ninety-four percent of the employees perceived the workday as very long, 79% were dissatisfied with the work schedule, while 61% of the employees perceived the summer work environment as extremely hot. Ergonomics should be considered in the work system design so as to reduce or eliminate problems in oilrigs in hot desert environments. (+info)
Southern Peru desert shattered by the great 2001 earthquake: implications for paleoseismic and paleo-El Nino-Southern Oscillation records.
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In the desert region around the coastal city of Ilo, the great southern Peru earthquake of June 23, 2001 (8.2-8.4 moment magnitude), produced intense and widespread ground-failure effects. These effects included abundant landslides, pervasive ground cracking, microfracturing of surficial hillslope materials, collapse of drainage banks over long stretches, widening of hillside rills, and lengthening of first-order tributary channels. We have coined the term "shattered landscape" to describe the severity of these effects. Long-term consequences of this landscape shattering are inferred to include increased runoff and sediment transport during postearthquake rainstorms. This inference was confirmed during the first minor postearthquake rainstorm there, which occurred in June and July of 2002. Greater amounts of rainfall in this desert region have historically been associated with El Nino events. Previous studies of an unusual paleoflood deposit in this region have concluded that it is the product of El Nino-generated precipitation falling on seismically disturbed landscapes. The effects of the 2001 earthquake and 2002 rainstorm support that conclusion. (+info)
Reconstructing the origin of Helianthus deserticola: survival and selection on the desert floor.
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The diploid hybrid species Helianthus deserticola inhabits the desert floor, an extreme environment relative to its parental species Helianthus annuus and Helianthus petiolaris. Adaptation to the desert floor may have occurred via selection acting on transgressive, or extreme, traits in early hybrids between the parental species. We explored this possibility through a field experiment in the hybrid species' native habitat using H. deserticola, H. annuus, H. petiolaris, and two populations of early-generation (BC(2)) hybrids between the parental species, which served as proxies for the ancestral genotype of the ancient hybrid species. Character expression was evaluated for each genotypic class. Helianthus deserticola was negatively transgressive for stem diameter, leaf area, and flowering date, and the latter two traits are likely to be advantageous in a desert environment. The BC(2) hybrids contained a range of variation that overlapped these transgressive trait means, and an analysis of phenotypic selection revealed that some of the selective pressures on leaf size and flowering date, but not stem diameter, would move the BC(2) population toward the H. deserticola phenotype. Thus, H. deserticola may have originated from habitat-mediated directional selection acting on hybrids between H. annuus and H. petiolaris in a desert environment. (+info)
On the origin of the desert locust Schistocerca gregaria (Forskal) (Orthoptera: Acrididae: Cyrtacanthacridinae).
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The locust genus Schistocerca (Stal) has a transatlantic disjunction, which has been controversial for more than a century. Among 50 species within the genus, only one species, the desert locust (S. gregaria Forskal), occurs in the Old World, and the rest occur in the New World. Earlier taxonomists suggested that the desert locust is a migrant from America, but this view was strongly challenged when a large swarm of the desert locust successfully crossed the Atlantic Ocean from West Africa to the West Indies in 1988. The currently accepted view, supported by this incident, is that the New World species are descendants of a gregaria-like ancestor, and the desert locust would be ancestral to the rest of the genus. However, there is surprisingly little evidence to support this view other than the 1988 swarm. I present the most comprehensive phylogenetic study that suggests that the desert locust originated from the New World, contrary to the accepted view. I also present a hypothesis about how the ancestral Schistocerca might have colonized the New World in the first place in light of phylogenetic relationships with other cyrtacanthacridine genera. (+info)
Path integration in desert ants, Cataglyphis: how to make a homing ant run away from home.
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Path integration is an ant's lifeline on any of its foraging journeys. It results in a homebound global vector that continually informs the animal about its position relative to its starting point. Here, we use a particular (repeated training and displacement) paradigm, in which homebound ants are made to follow a familiar landmark route repeatedly from the feeder to the nest, even after they have arrived at the nest. The results show that during the repeated landmark-guided home runs the ant's path integrator runs continually, so that the current state of the homebound vector increasingly exceeds the reference state. The dramatic result is that the homing ants run away from home. This finding implies that the ants do not rely on cartographic information about the locations of nest and feeder (e.g. that the nest is always south of the feeder), but just behave according to what the state of their egocentric path integrator tells them. (+info)
Mutactimycin PR, a new anthracycline antibiotic from Saccharothrix sp. SA 103. I. Taxonomy, fermentation, isolation and biological activities.
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In the course of screening for new antibacterial agents, a new isolate collected from a soil sample of an arid area in south Algeria, produced a red pigment which was shown an antagonistic action against a gram-positive bacterium Bacillus subtilis. The isolate was identified as Saccharothrix sp. and named SA 103. The red pigment, eluted by HPLC on reverse phase C18 column, contained two compounds of an anthracycline antibiotics group. The structure of the major product (2) was characterized as mutactimycin C, and PR (1) was a new member of this group, designated as mutactimycin PR. These compounds showed an antibiotic activity against certain gram-positive bacteria in vitro. This is the first report of mutactimycins production by the genus Saccharothrix. (+info)
Rhizosheath of sinai desert plants is a potential repository for associative diazotrophs.
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Among 42 plant species representing the flora of north Sinai, two possessed sand grain sheath encasing the roots. They are Panicum turgidum Forssk. and Stipagrostis scoparia (Trin.and Rupr.) deWinter. Rhizosheaths, compared to surrounding free sand, accommodated higher population density of microorganisms including associative diazotrophs. Isolates secured belonged to the species of Bacillus circulans, Paenib. macerans (Bacillus macerans), Enterobacter agglomerans, Agrobacterium radiobacter and Chryseomonas luteola (Pseudomonos luteola). The rhizosheath potentiality in re-vegetating sand dunes and arid lands, through nitrogen fixation, plant-water relationship and root continuity for nutrient uptake, are discussed. (+info)