geotaxis

Geotaxis is a directional movement or orientation of an organism in response to gravity. It is observed in many species and can be classified as positive geotaxis (movement toward the gravitational pull, typically downward) or negative geotaxis (movement away from gravity, typically upward). Geotaxis describes locomotor responses, whereas gravitropism or geotropism are terms commonly used for growth-oriented responses to gravity, especially in plants.

Mechanisms of geotaxis often involve gravity-sensing structures and sensory pathways that influence motor output. In many animals, specialized cells or organs detect the pull of gravity, and this information is integrated with other sensory cues to guide movement. In aquatic and terrestrial organisms, statoliths or analogous gravity-sensing elements help determine direction relative to the vertical axis.

Examples and applications vary by group. In the fruit fly Drosophila melanogaster, negative geotaxis is illustrated by climbing behavior in which individuals move upward after being tapped to the bottom of a vial. In nematodes such as Caenorhabditis elegans, geotaxis can affect vertical distribution in a containment column under certain conditions. Some microorganisms, including certain bacteria and algae, exhibit gravitactic movement that biases motion along the gravity axis, often influenced by buoyancy and motility mechanisms.

Geotaxis is used in behavioral and physiological studies to understand navigation, sensorimotor integration, and how organisms orient themselves in complex environments, including laboratory assays and ecophysiological contexts.