INFLUENCE OF LIGHT OF VERY LOW INTENSITY ON PHOTOTROPIC REACTIONS OF ANIMALS

Area of Science:

• Animal behavior
• Photobiology
• Crustacean physiology

Background:

• Negative phototropism is a common behavior in terrestrial invertebrates.
• Understanding the mechanisms of phototropism is crucial for explaining animal navigation and habitat selection.
• Previous research has established the photochemical basis of phototropism in some marine invertebrates.

Purpose of the Study:

• To quantitatively investigate the negative phototropism of land isopods across a wide range of light intensities.
• To determine the relationship between light intensity and the angular response in land isopods.
• To explore the underlying mechanisms of phototropism in these crustaceans.

Main Methods:

• Measuring the angular deflection of land isopods in response to light stimuli.
• Conducting experiments across various light intensities, including low levels.
• Analyzing the relationship between light intensity and turning angle.

Main Results:

• Maximal turning responses (approx. 55 degrees for Oniscus) were observed above 0.0026 m.c. light intensity.
• Anatomical features, specifically the carapace, limit the maximal turning angle.
• Below 0.0026 m.c., angular deflection decreased logarithmically with light intensity, becoming negligible at 0.00003 m.c.

Conclusions:

• The phototropic response in land isopods is proportional to the logarithm of light intensity.
• This relationship supports a photochemical model for phototropism, aligning with Loeb's theory.
• Anatomical adaptations play a significant role in shaping the specific phototropic responses observed in different land isopod species.