121 research outputs found
Oscillatory surface rheotaxis of swimming E. coli bacteria
Bacterial contamination of biological conducts, catheters or water resources
is a major threat to public health and can be amplified by the ability of
bacteria to swim upstream. The mechanisms of this rheotaxis, the reorientation
with respect to flow gradients, often in complex and confined environments, are
still poorly understood. Here, we follow individual E. coli bacteria swimming
at surfaces under shear flow with two complementary experimental assays, based
on 3D Lagrangian tracking and fluorescent flagellar labelling and we develop a
theoretical model for their rheotactic motion. Three transitions are identified
with increasing shear rate: Above a first critical shear rate, bacteria shift
to swimming upstream. After a second threshold, we report the discovery of an
oscillatory rheotaxis. Beyond a third transition, we further observe
coexistence of rheotaxis along the positive and negative vorticity directions.
A full theoretical analysis explains these regimes and predicts the
corresponding critical shear rates. The predicted transitions as well as the
oscillation dynamics are in good agreement with experimental observations. Our
results shed new light on bacterial transport and reveal new strategies for
contamination prevention.Comment: 12 pages, 5 figure
Reproduction triggers adaptive increases in body size in female mole-rats
In social mole-rats, breeding females are larger and more elongated than non-breeding female helpers. This status-related morphological divergence is thought to arise from modifications of skeletal growth following the death or removal of the previous breeder and the transition of their successors from a non-breeding to a breeding role. However, it is not clear what changes in growth are involved, whether they are stimulated by the relaxation of reproductive suppression or by changes in breeding status, or whether they are associated with fecundity increases. Here, we show that, in captive Damaraland mole-rats (Fukomys damarensis), where breeding was experimentally controlled in age-matched siblings, individuals changed in size and shape through a lengthening of the lumbar vertebrae when they began breeding. This skeletal remodelling results from changes in breeding status because (i) females removed from a group setting and placed solitarily showed no increases in growth and (ii) females dispersing from natural groups that have not yet bred do not differ in size and shape from helpers in established groups. Growth patterns consequently resemble other social vertebrates where contrasts in size and shape follow the acquisition of the breeding role. Our results also suggest that the increases in female body size provide fecundity benefits. Similar forms of socially responsive growth might be more prevalent in vertebrates than is currently recognized, but the extent to which this is the case, and the implications for the structuring of mammalian dominance hierarchies, are as yet poorly understood.The Kalahari Mole-rat Project is supported by a European Research Council Grant awarded to T.C.-B. (no. 294494); J.T. was funded by a Natural Environment Research Council Doctoral Training Program; parts of the fieldwork were funded by a British Ecological Society Grant awarded to Markus Zöttl (no. 5301/6343).http://rspb.royalsocietypublishing.org2019-06-13hj2018Mammal Research InstituteZoology and Entomolog
Periodic and Quasiperiodic Motion of an Elongated Microswimmer in Poiseuille Flow
We study the dynamics of a prolate spheroidal microswimmer in Poiseuille flow
for different flow geometries. When moving between two parallel plates or in a
cylindrical microchannel, the swimmer performs either periodic swinging or
periodic tumbling motion. Although the trajectories of spherical and elongated
swimmers are qualitatively similar, the swinging and tumbling frequency
strongly depends on the aspect ratio of the swimmer. In channels with reduced
symmetry the swimmers perform quasiperiodic motion which we demonstrate
explicitely for swimming in a channel with elliptical cross section
Variation in growth of Damaraland mole-rats is explained by competition rather than by functional specialization for different tasks
In some eusocial insect societies, adaptation to the division of labour results in multimodal size
variation among workers. It has been suggested that variation in size and growth among nonbreeders
in naked and Damaraland mole-rats may similarly reflect functional divergence associated
with different cooperative tasks. However, it is unclear whether individual growth rates are
multimodally distributed (as would be expected if variation in growth is associated with
specialisation for different tasks) or whether variation in growth is unimodally distributed, and is
related to differences in the social and physical environment (as would be predicted if there are
individual differences in growth but no discrete differences in developmental pathways). Here we
show that growth trajectories of non-breeding Damaraland mole-rats vary widely, and that their
distribution is unimodal, contrary to the suggestion that variation in growth is the result of
differentiation into discrete castes. Though there is no evidence of discrete variation in growth,
social factors appear to exert important effects on growth rates and age-specific size, which are both
reduced in large social groups.This study was funded by an European Research Council grant to THCB (294494).http://rsbl.royalsocietypublishing2017-12-31hb2017Zoology and Entomolog
Evaluating the Risk of Air Pollution to Forests in Central and Eastern Europe
Foliar damage to trees by air pollution in Central and Eastern Europe has been a major scientific and political issue. Emissions of toxic gases such as sulfur dioxide and nitrogen oxides can have wide-ranging effects on local and regional vegetation that can be compounded by other environmental stresses to plant growth. Since uptake and physiological effects of these gases on tree leaves are largely mediated by stomata, surrogate methods for estimating pollutant conductances into leaves and forest canopies may lead to risk assessments for major vegetation types that can then be used in regional planning. Management options to ameliorate or mitigate air pollutant damage to forests and losses in productivity are likely to be more difficult to widely implement than on-the-stack emissions abatement, Informed management and policy decisions regarding Central and Eastern European forests are dependent on the development of quantitative tools and models for risk assessment of the effects of atmospheric pollutants on ecosystem health and productivity
Electron impact excitation of methane: determination of appearance energies for dissociation products
Mineralisationsuntersuchungen in der Malcolmia cephallenica-und der cerastiumarabis verna-assoziation auf Kephallinia
An Integrated Watershed/Plot-Scale Study of Element Cycling in Spruce Ecosystems of the Black Forest
The effects of recruitment to direct predator cues on predator responses in meerkats
Behavioral responses of animals to direct predator cues (DPC; e. g. urine) are common
and may improve their survival. We investigated wild meerkat (Suricata suricatta) responses
to DPCs by taking an experimental approach. When meerkats encounter a DPC they often
recruit group members by emitting a call type, which causes the group members to interrupt
foraging and approach the caller. The aim of this study was to identify the qualities of
olfactory predator cues, which affect the strength of response by meerkats, and determine the
benefits of responses to such cues. Experimental exposure to dog (Canis lupus) urine as a
DPC revealed that the recruited individuals increased vigilance to fresh urine in comparison to
older urine, whereas a higher quantity of urine did not induce such an effect. Both freshness
and higher quantities increased the proportion of group members recruited. These results indicate that recruitment might play a crucial role in correctly assessing the current level of
danger and that recruiting might facilitate group decision-making. To test the prediction that
the reaction to a DPC enhances early predator response, we presented a DPC of a predator and
a control cue of a herbivore, and each time simultaneously moved a full-mounted caracal
(Caracal caracal) in the vicinity of the group. Meerkats responded earlier to the caracal when
the DPC was presented, indicating that the response to a DPC facilitates predator response
and that they use information from the cue that reliably reflects the risk in the current
moment.This work was supported by a âFörderungstipendiumâ and a âKWAâ from the University
of Vienna to MZ covering travel costs to him, the Zoological Institute of the University of
Zurich to MBM for all research expenses in the field due to this study, and Cambridge and Zurich University for financing the long term field project.http://beheco.oxfordjournals.org/hb201
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