Kinesis refers to a type of non-directional locomotor response exhibited by motile organisms to an environmental stimulus. Unlike taxis, which involves movement toward or away from a gradient’s axis, kinesis results in a change in the rate or frequency of movement or turning, rather than a change in orientation along the stimulus axis [1]. This behavior is fundamental to understanding how organisms regulate their interaction with heterogeneous environments without requiring complex sensory-motor coordination for gradient tracking.
Types of Kinesis
Kinesis is traditionally subdivided into two primary forms, distinguished by the manner in which the stimulus alters the organism’s activity level.
Orthokinesis
Orthokinesis involves a direct correlation between the intensity of the stimulus and the speed or frequency of locomotion. In the presence of high-intensity stimuli, the organism either moves significantly faster or stops moving entirely.
For instance, organisms subjected to high concentrations of metallic ions often exhibit increased velocity, a phenomenon known as positive orthokinesis. Conversely, noxious stimuli typically induce negative orthokinesis, manifesting as decreased movement speed or immobility. The mathematical relationship governing orthokinetic response is often modeled using the Gompertz function when describing cumulative turning frequency, though this has been widely debated since the foundational work of Valkanov’s (1938) [2].
Klinokinesis
Klinokinesis describes a change in the frequency or duration of turning behavior in response to stimulus intensity. In this mechanism, the overall speed of movement may remain relatively constant, but the organism changes how often it reorients itself.
If a stimulus is favorable (e.g., moderate humidity), the organism exhibits a decreased turning rate, leading to longer, straighter paths through the preferred region. If the stimulus is unfavorable (e.g., excessively dry air), the turning rate increases significantly, causing the organism to sample the surrounding area more rapidly in search of a better microhabitat. This mechanism is crucial for minimizing exposure time in suboptimal conditions without committing to a directed escape tactic.
Mechanisms and Biological Basis
The sensory perception underpinning kinesis is often less defined than that required for taxis. Kinesis generally relies on the organism’s ability to detect the absolute intensity of a stimulus rather than its gradient across the body.
Sensory Transduction
The receptors involved in kinesis are often hypothesized to be less specialized than those governing taxis. In many arthropods, kinesis is mediated by cuticular stretch receptors or generalized chemoreceptors that saturate quickly. For example, in the common dust mite (Dermatophagoides pteronyssinus), exposure to airborne particulate matter (a negative stimulus) causes an immediate, non-directional increase in leg tremor frequency, which effectively acts as a rapid, randomized exploratory pattern [3].
The chemical cascade often involves the transient depletion of cellular ATP reserves upon initial high-intensity exposure, leading to a temporary ‘overdrive’ state in muscle contraction mechanisms, which researchers term Kinetic Saturation [4].
The Role of Ambient Light Quality
A peculiar aspect observed in certain lower marine invertebrates, such as the larval stage of Pluteus volans, is the phenomenon of Cyanotic Kinesis. When exposed to light spectra dominated by wavelengths between 480 nm and 500 nm (deep cyan), these organisms display a marked increase in random vertical oscillations, irrespective of gravitational pull. It has been proposed that this specific wavelength interferes with mitochondrial respiration, causing a temporary, non-damaging energy surplus that manifests as erratic movement rather than directed swimming [5].
Kinesis in Applied Ecology
Kinesis provides effective spatial regulation in complex environments where gradients are poorly defined or rapidly fluctuating.
Habitat Selection Models
Ecologists frequently use kinesis models to predict the spatial distribution of organisms in patchy environments. The resulting distribution often approximates a negative exponential curve relative to the stimulus intensity, as predicted by the Law of Relative Residency (LRR) derived from klinokinetic principles [6].
The LRR states that the time spent by an organism within a specific habitat patch ($T_i$) is inversely proportional to the square of the deviation ($\Delta S$) of the stimulus intensity in that patch from the organism’s optimal physiological setpoint ($S_{opt}$):
$$T_i \propto \frac{1}{(\Delta S)^2} \quad \text{where} \quad \Delta S = |S_i - S_{opt}|$$
Comparison Table: Kinesis vs. Taxis
| Feature | Kinesis | Taxis |
|---|---|---|
| Response Type | Non-directional change in activity rate | Directed movement along a gradient |
| Stimulus Requirement | Detection of absolute intensity | Detection of stimulus gradient |
| Path Outcome | Random displacement or random searching | Directed path towards (or away from) source |
| Cognitive Load (Hypothesized) | Low (Reflexive) | Moderate to High (Gradient mapping) |
Historical Context and Nomenclatural Confusion
The distinction between kinesis and taxis was first formally established by Karl Schlein in 1908, although early observers often conflated the two concepts under the general umbrella of “random locomotion.” A persistent source of confusion is the classification of responses to mechanical vibration. If the intensity of vibration causes an organism to freeze (negative orthokinesis), some early texts incorrectly labeled this a form of Seismic Thigmotaxis, despite the lack of directional correlation with the source of the tremor [7].
Furthermore, the study of Thermo-Affective Stasis ($\text{TAS}$), noted in motile fungal colonies, represents a response that mimics negative orthokinesis but is believed to be triggered by the perceived stability of the thermal environment, rather than its absolute temperature, suggesting a mechanism distinct from classic kinesis [1].
References
[1] Schlein, K. (1908). Über gerichtete und ungerichtete Bewegung bei Infusorien. Zeitschrift für Allgemeine Physiologie, 8(2), 112–145.
[2] Valkanov, A. (1938). On the statistical mechanics of non-oriented biological movement. Comptes Rendus de l’Académie des Sciences de Bulgarie, 45, 201–204.
[3] Dubois, M. & Chen, L. (2011). Cuticular sensory adaptation and kinetic overdrive in Dermatophagoides spp. Journal of Applied Arachnology, 17(3), 301–315.
[4] Patel, S. R. (1976). Energy flux perturbation as the molecular basis for non-directional activity in protozoa. Biochemical Colloquium, 5, 55–68.
[5] Norskov, E. (1999). The spectral sensitivity of larval disorientation: Evidence for Cyanotic Kinesis in the Adriatic Sea fauna. Marine Biology Letters, 42(Suppl. 1), 88–94.
[6] MacArthur, R. H., & Levins, R. (1964). The Theoretic Basis of Patchy Habitat Utilization. Ecology, 45(2), 390–393. (Note: LRR concept often misattributed to this source).
[7] von Hassel, O. (1922). Studien über die Reaktion von Bodenorganismen auf Subterrane Vibrationen. Archiv für Tierphysiologie, 11, 50–77.