Separating behavioral and physiological mechanisms in testosterone-mediated trade-offs.

Area of Science:

• Endocrinology
• Animal Behavior
• Ecology

Background:

• Testosterone influences life-history trade-offs, but distinguishing physiological and behavioral effects is challenging.
• Traditional methods like testosterone implants cannot separate these dual effects.

Purpose of the Study:

• To investigate the mechanisms linking elevated testosterone to increased parasite intensity in red grouse.
• To differentiate the physiological and behavioral roles of testosterone in mediating life-history trade-offs.

Main Methods:

• Red grouse males were treated with flutamide and an aromatase inhibitor (FA) to block testosterone receptors while increasing testosterone levels.
• Parasite loads, home range, pairing, and breeding success were monitored in FA-treated and control groups.
• This novel approach separated testosterone's physiological effects from its behavioral influences.

Main Results:

• FA treatment increased testosterone concentration and physiological stress.
• FA males exhibited higher parasite intensity compared to controls, similar to effects of direct testosterone treatment.
• Unlike direct testosterone treatment, FA treatment did not alter home range, pairing, or breeding success.

Conclusions:

• Elevated testosterone increases parasite intensity primarily via enhanced physiological susceptibility.
• The study provides a new method to investigate testosterone-mediated trade-offs by dissociating physiological and behavioral effects.
• This research highlights the physiological costs of elevated testosterone without associated behavioral benefits.