Biomedical subjects
Publications and source records attributed to W I Sellers.
UNLABELLED: Yeast Exploration Tool Integrator (YETI) is a novel bioinformatics tool for the integrated visualization and analysis of functional genomic data sets from the budding yeast Saccharomyces cerevisiae. AVAILABILITY: YETI is freely available for use over the WWW, or download under license, at http://www.bru.ed.ac.uk/~orton/yeti.html
To understand the evolution of bipedalism among the hominoids in an ecological context we need to be able to estimate the energetic cost of locomotion in fossil forms. Ideally such an estimate would be based entirely on morphology since, except for the rare instances where footprints are preserved, this is the only primary source of evidence available. In this paper we use evolutionary robotics techniques (genetic algorithms, pattern generators and mechanical modeling) to produce a biomimetic simulation of bipedalism based on human body dimensions. The mechanical simulation is a seven-segment, two-dimensional model with motive force provided by tension generators representing the major muscle groups acting around the lower-limb joints. Metabolic energy costs are calculated from the muscle model, and bipedal gait is generated using a finite-state pattern generator whose parameters are produced using a genetic algorithm with locomotor economy (maximum distance for a fixed energy cost) as the fitness criterion. The model is validated by comparing the values it generates with those for modern humans. The result (maximum efficiency of 200 J m(-1)) is within 15% of the experimentally derived value, which is very encouraging and suggests that this is a useful analytic technique for investigating the locomotor behaviour of fossil forms. Initial work suggests that in the future this technique could be used to estimate other locomotor parameters such as top speed. In addition, the animations produced by this technique are qualitatively very convincing, which suggests that this may also be a useful technique for visualizing bipedal locomotion.
This paper reports 3-dimensional confocal microscopy observations on how nephrogenic aggregates form from the NCAM- and Pax2-positive caps (4-5 cells deep) of condensed metanephric mesenchyme surrounding the duct tips of the mouse kidney. Aggregates of 6-8 cells are first seen at approximately E12.5-12.75 immediately proximal to this cap, closely abutting the duct surface. As the tip advances, NCAM expression is maintained in the cap but is otherwise restricted to aggregates whose cells rapidly epithelialise, forming tubules that invade the duct epithelium. Pax2 expression studies shows how the rind of nephrogenic blastemal cells forms: as duct tips extend towards the kidney surface, the associated Pax2+ cells form patches of cells on the kidney surface. These observations revise our knowledge of the timing and process of nephron initiation.
Unlike all other primates, members of the subfamily Lorisinae are never seen to leap. To investigate the anatomical specializations that are behind the absence of leaping in their locomotor repertoire, a predictive mechanical model of leaping was developed using the lesser bushbaby, Galago moholi, as a size-matched leaping prosimian comparison. This enabled the required limb movements for a leaping slender loris to be calculated, and hence the torque and power requirements at each of the hindlimb joints. From this information, the maximum feasible leap was calculated for the slender loris morphotype; and it was found that this alone would prevent the animal from leaping a greater distance than it could walk over, so that the reduction in fitness due to an apparent loss of leaping from the behavioural repertoire can be considered to be very small.
We tend to assume that natural selection will bring about 'optimal' configurations in morphology and behaviour. Jumping locomotion involves large forces and energy costs which, in this non-cyclic activity, are generated anew with each jump. Jumping appears to be, therefore, a major target for optimization. It has been a standard assumption that jumpers will tend to adopt ballistic paths which will minimize the energy costs involved in jumping, and will act to minimize the loads applied to the body. Experimental studies, using kinematic analysis of digitized video recordings of the jump in five prosimian primates, with a 25-fold range in body mass, show that most do not adopt energy-efficient paths until the length of the jump is close to the maximum they can attain. Statistical analysis of quantified field observations suggests that, of three primate jumpers, only the largest, most unspecialized appears to take the forces applied to the musculoskeletal system into consideration when selecting supports used in locomotion. 'Ecological' factors, such as time pressure and habitat support density, may thus be the prime consideration for many species in determining the manner in which they jump.
Accelerometry data were transmitted by a radio collar attached to a hand-reared red-ruffed lemur housed in a large indoor/outdoor enclosure at Chester Zoo. An observer simultaneously recorded locomotor behaviour using a manually operated event recorder. Both data streams were recorded directly to hard disk to ensure accurate synchrony. Leaps were modelled using a y = x2 - x3 formulation for the take-off acceleration, to link peak acceleration to leap distance. Cyclic locomotor modes were analysed using power spectra and the modal frequency used to estimate stride periodicity. Comparison of the dual data shows that leaping behaviour can be recorded reliably, and acceleration magnitude provides accurate predictions of the distance travelled. Cyclic activities were less well characterised, but calibration should permit travel distance estimations equalling or bettering those from conventional techniques.