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)
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This process occurs within seconds to hours and is driven by the movement (dispersion or aggregation) of pigment granules inside chromatophores.
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It is regulated by the frog’s neuromuscular or neuroendocrine systems, often in response to external stimuli such as background colour, temperature, or stress.
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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)
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This process takes days to months and involves changes in the number and density of chromatophores in the skin.
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It is typically associated with longer-term environmental changes, such as seasonal shifts or breeding cycles.
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Morphological changes can be permanent or semi-permanent, such as those associated with sexual maturity or breeding.
Types of Chromatophores Involved:
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Melanophores: Contain black/brown melanin pigment.
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Xanthophores: Contain yellow pigments.
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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
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By matching their skin colour to their surroundings, frogs can avoid detection by predators and increase their chances of survival.
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For example, frogs darken on dark backgrounds and lighten on light backgrounds to blend in.
2. Thermoregulation
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As ectotherms, frogs regulate their body temperature by absorbing or reflecting heat.
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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
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Some tree frogs change colour during the breeding season to attract mates or signal reproductive readiness (dynamic dichromatism).
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These changes can be temporary (reverting after the season) or permanent (associated with sexual maturity).
- 4. Stress and Physiological State
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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.