Elevated Testosterone Is Required for Male Sexual Behaviour and Dynamic Colour Change in Veiled Chameleons

Area of Science:

• Reproductive Biology
• Animal Behavior
• Endocrinology

Background:

• Sex-specific genotypes and early development influence sexually dimorphic traits in vertebrates.
• The veiled chameleon (Chamaeleo calyptratus) with XX/XY sex chromosomes serves as a model for studying these influences.

Purpose of the Study:

• To investigate the role of testosterone in the expression of male-typical behavior and color change in veiled chameleons.
• To determine if testosterone alone is sufficient for these sexually dimorphic traits.

Main Methods:

• Hormonal manipulations were performed, including castration with and without testosterone replacement in males.
• Testosterone was administered to females to assess its effects.

Main Results:

• Elevated testosterone induced male-typical sexual behavior and bright color changes in females.
• Castration suppressed these traits in males, indicating testosterone's sufficiency.
• High testosterone levels resulted in indiscriminate courtship behavior, suggesting visual cues may be unreliable for sex recognition.

Conclusions:

• The development of male-typical sexual behavior and color change in chameleons is dependent on elevated androgen levels.
• This contrasts with skeletal traits, which develop independently of androgens in castrated males.
• The ontogeny of sex-typical phenotypes in chameleons involves diverse mechanisms.