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A Quantitative Approach to Movement, Displacement, and Mobility of Protozoa
Author(s) -
Ricci Nicola,
Barbanera Filippo,
Erra Fabrizio
Publication year - 1998
Publication title -
journal of eukaryotic microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 1066-5234
DOI - 10.1111/j.1550-7408.1998.tb04556.x
Subject(s) - ciliate , biology , displacement (psychology) , dimensionless quantity , diffusion , biological system , statistics , physics , mathematics , ecology , mechanics , thermodynamics , psychology , psychotherapist
Diffusion theory can completely describe the movement of a ciliate along a track of a certain length (L), travelled in a time (t), and with the extremes lying at a distance D. Three important descriptors of this behavior are: (1) the kinetic index (I k = L/t), namely the average velocity in μm/s, which expresses the state of the “accelerator” of the ciliate; (2) the geometric index (I g = D/L) measuring the straightness of the track by a dimensionless number. 0 ≤ I g ≤ 1, which expresses the state of the “steering wheel” and represents a sort of “directional efficiency”; and (3) the displacement rate (R d = D/t), integrating the first two indices and expressing the combined effect of the “accelerator” and the “steering wheel” of the organism with a unique measure (in μm/s), which defines the average displacement rate or the effectiveness of the track in displacing the organism in space. A weighted estimate of general mobility is given by the mobility rate [R mo = (R̄ d .f) creeping ‐ (R̄ d .f) swimming ], obtained by multiplying the average R d of the creeping organisms and the average R d of the swimming organisms by their relative frequencies of occurrence (f), and adding the two products. Values for experimental populations of Oxytricha bifaria (Ciliata, Hypotrichida) maintained at 24, 19, 14, and 9° C demonstrated both the appropriateness and the usefulness of these indices and rates to describe the tracks a posteriori, and to provide measures to reason about their possible adaptive significance.