Limits of thermal sensation

Area of Science:

• Thermoreception and Sensory Biology
• Environmental Physiology
• Biophysics

Background:

• Understanding the limits of biological thermal sensitivity is crucial for explaining sensory perception in various organisms.
• Existing research compares receptor sensitivity to environmental thermal signals and internal thermal noise.

Purpose of the Study:

• To compare the sensitivity of known thermal receptors with physical limits imposed by thermal noise.
• To derive expressions for minimal detectable thermal gradients for moving organisms.
• To evaluate the plausibility of thermal sensing mechanisms, such as nematodes locating plant roots.

Main Methods:

• Theoretical analysis comparing biological sensitivity with biophysical limits of thermal noise.
• Derivation of mathematical expressions for minimal detectable thermal gradients.
• Review and discussion of thermal sensing capabilities across diverse taxa (nematodes, bacteria, slime mold, rattlesnakes, mammals).

Main Results:

• The most sensitive known biological thermal responses are significantly less sensitive than theoretically possible.
• Biological thermal receptors possess sufficient sensitivity to detect biologically relevant environmental thermal signals.
• Minimal detectable thermal gradients for moving organisms were derived, with environmental gradients (e.g., soil > 10^-3 °C/cm) often exceeding receptor sensitivity limits.

Conclusions:

• Biological thermal sensing is constrained by physical limits but is adequate for detecting environmental cues.
• Thermal fluctuations within receptors are likely below 10^-6 °C, far below the sensitivity of reported biological responses.
• The hypothesis of nematodes using heat production to locate plant roots is unlikely due to insufficient thermal gradients.