Relative expression of insulin-like growth factor I (IGF-I) mRNA in the manakin testosterone (T) treatment study, zebra finch flutamide treatment study, and species comparison stud.
(A) Manakin T treatment study; white-bars represent male manakins treated with T-filled implants, and black bars represent male manakins treated with blank implants (Control). (B) Zebra finch flutamide study; white bars represent male zebra finches treated with T-filled implants and blank implants (T+Blank), and black bars represent male zebra finches treated with T-filled implants and flutamide-filled implants (T+Flutamide). (C) Species comparison of reproductively active male birds. White bars represent golden-collared manakins, grey bars represent ochre-bellied flycatchers, and black bars represent zebra finches. Wing muscles are displayed on the horizontal axis in all graphs (supracoracoideus = SC; scapulohumeralis caudalis = SH; and pectoralis = PEC). Asterisks (*) displayed within each graph’s legend indicate significant differences between hormone manipulated groups (A & B) and among species (C). Data represent means ±1 SEM.