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Green Tree Frog Skin Colour

Green tree frogs can rapidly alter their skin colour through physiological and morphological processes involving specialized skin cells called chromatophores. There are two main mechanisms:

1. Physiological Colour Change (Rapid, Reversible)

  • This process occurs within seconds to hours and is driven by the movement (dispersion or aggregation) of pigment granules inside chromatophores.

  • It is regulated by the frog’s neuromuscular or neuroendocrine systems, often in response to external stimuli such as background colour, temperature, or stress.

  • For example, a frog placed on a brown tree trunk may quickly turn brown to blend in, and then revert to green when returned to a leafy background.

2. Morphological Colour Change (Slower, Long-Term)

  • This process takes days to months and involves changes in the number and density of chromatophores in the skin.

  • It is typically associated with longer-term environmental changes, such as seasonal shifts or breeding cycles.

  • Morphological changes can be permanent or semi-permanent, such as those associated with sexual maturity or breeding.

Types of Chromatophores Involved:

  • Melanophores: Contain black/brown melanin pigment.

  • Xanthophores: Contain yellow pigments.

  • Iridophores: Reflect light, producing iridescent or blue/green hues.

The interplay between these chromatophores, and their pigment distribution, creates the range of colours seen in green tree frogs.

Why Green Tree Frogs Change Colour

Green tree frogs change their skin colour for several adaptive reasons:

1. Camouflage

  • By matching their skin colour to their surroundings, frogs can avoid detection by predators and increase their chances of survival.

  • For example, frogs darken on dark backgrounds and lighten on light backgrounds to blend in.

2. Thermoregulation

  • As ectotherms, frogs regulate their body temperature by absorbing or reflecting heat.

  • Darker colours absorb more heat, which is beneficial in cooler environments, while lighter colours reflect heat, helping the frog stay cool in warmer conditions.

3. Communication and Breeding

  • Some tree frogs change colour during the breeding season to attract mates or signal reproductive readiness (dynamic dichromatism).

  • These changes can be temporary (reverting after the season) or permanent (associated with sexual maturity).

  • 4. Stress and Physiological State

  • Sudden colour changes can also occur in response to stress, such as handling, temperature shifts, or other environmental pressures.

Summary Table: How and Why Green Tree Frogs Change Colour

Mechanism

Speed

Purpose

Example Trigger

Physiological (PCC)

Seconds–hours

Camouflage, thermoregulation, stress

Background change, temperature, stress

Morphological (MCC)

Days–months

Seasonal adaptation, breeding

Breeding season, long-term habitat change

In summary:
Green tree frogs change colour by adjusting the distribution and density of pigments in specialized skin cells, allowing them to camouflage, regulate temperature, communicate, or respond to stress. Rapid changes are typically for immediate adaptation, while slower changes serve long-term needs.

Green Tree Frogs Don’t Drink

Green tree frogs do not drink water with their mouths like mammals. Instead, they hydrate by absorbing water directly through their skin-a process known as cutaneous absorption.

Specialized Skin Regions

  • Pelvic Patch (Seat Patch):
    Green tree frogs, like many other amphibians, have a specialized area of skin on the underside of their bodies called the pelvic patch or seat patch. This region, which extends across the lower abdomen and hindlimbs, is especially adapted for rapid water uptake from moist surfaces or shallow water.

  • Skin Structure:
    The skin in these regions contains a dense network of capillaries and specialized cells, making it highly permeable to water. The presence of aquaporin proteins (water channels) in the skin cells further facilitates efficient water movement into the body.

How Water Absorption Works

  • Direct Absorption:
    When a green tree frog sits on a wet surface, water moves from the environment into the frog’s body through the skin by osmosis. This is driven by the difference in water concentration between the moist environment and the frog’s internal tissues.

  • Condensation Collection:
    During dry periods, green tree frogs have been observed sitting outside on cool nights. When they return to their warmer dens, condensation forms on their skin-much like fog on cold glass. The frogs then absorb this condensed moisture through their skin, helping them stay hydrated even when free water is scarce.

  • Efficiency:
    Studies have shown that green tree frogs can absorb up to 60% of each water drop that lands on their skin, making this method highly effective for hydration, especially in arid environments.

Additional Adaptations

  • Mucus Secretion:
    Their skin secretes a thin layer of mucus, which not only helps retain moisture but also aids in the absorption process and provides antibacterial and antiviral protection.