Male sexual behavior does not require elevated testosterone in a lizard (Coleonyx elegans, Eublepharidae).

Area of Science:

• Endocrinology
• Evolutionary Biology
• Behavioral Neuroscience

Background:

• Male sexual behavior in vertebrates is typically dependent on gonadal androgens.
• Sexual behavior comprises distinct appetitive (courtship) and consummatory (mounting) phases, potentially with differing hormonal regulation.
• The lizard family Eublepharidae possesses ancestral courtship displays activated by testosterone (T).

Purpose of the Study:

• To investigate the hormonal mechanisms underlying the simplified sexual behavior in Coleonyx elegans (Yucatan Banded Gecko).
• To determine if testosterone (T) is required for the mounting phase of sexual behavior in C. elegans.
• To examine the effects of exogenous T on sexual behavior in female C. elegans.

Main Methods:

• Surgical castration and testosterone replacement in adult male C. elegans.
• Implantation of adult female C. elegans with exogenous T.
• Observation and analysis of sexual behaviors in manipulated individuals.

Main Results:

• Expression of simplified sexual behavior in C. elegans males did not require elevated circulating testosterone (T).
• Exogenous T induced male-like mounting behavior in female C. elegans.
• The mounting phase of sexual behavior in C. elegans appears organized by androgens rather than directly activated by circulating T.

Conclusions:

• The evolution of simplified male sexual behavior in C. elegans involved the loss of androgen-activated courtship and retention of androgen-organized mounting.
• Mounting behavior in C. elegans exhibits a prolonged sensitivity to androgenic steroids, independent of current circulating T levels.
• This study reveals a novel pattern of androgenic control over sexual behavior in reptiles, distinct from many other vertebrate models.