Testosterone and year-round territorial aggression in a tropical bird.
Testosterone (T) regulates avian behaviors such as song and aggression during the breeding season. However, the role of T in year-round territorial birds is still enigmatic, especially in tropical birds. Spotted antbirds (Hylophylax n. naevioides) defend territories in the Panamanian rainforest year-round but have low plasma T levels (0.1-0.2 ng/ml), except during brief periods of social challenges. We manipulated T action in captive male Spotted antbirds to test whether this hormone is involved in the regulation of song and aggression. T-implants increased plasma androgen levels (T and dihydrotestosterone) and enhanced song in nonbreeding males. During a staged male-male encounter, T-implanted males sang more and were more aggressive than controls. In a second experiment, we blocked the two known T actions: its binding to androgen receptors and its conversion into estradiol by the enzyme aromatase. For this, we administered the androgen receptor antagonist flutamide (Flut) in combination with the aromatase inhibitor 1-4-6 androstatrien-3, 17-dione (ATD) to birds in breeding condition. ATD + Flut treatment significantly elevated plasma levels of luteinizing hormone, presumably via the lack of T feedback from its receptors. ATD + Flut-treated birds gave fewer spontaneous songs than control-implanted males. During staged male-male encounters, ATD + Flut-treated males did not sing at all and showed reduced aggressive behavior. Our data indicate that T can regulate aggressive behavior in these tropical birds. Although plasma T levels can be low year-round, Spotted antbirds may use T either by secreting it briefly during social challenges, by having a high sensitivity to T action, or by enzymatically converting circulating T precursors directly at the site of action. We hypothesize that plasma T levels are kept low in these year-round territorial birds to avoid potentially detrimental effects of tonically elevated T. Future treatment of nonbreeding birds with ATD + Flut will reveal whether T is indeed involved year-round in regulating aggressive behavior.
Hau
M
M
Department of Ecology, Ethology and Evolution, University of Illinois, Urbana, Illinois 61801, USA.
Wikelski
M
M
Soma
K K
KK
Wingfield
J C
JC
D000374:Aggression / Q000187:drug effects / Q000502:physiology*; D000726:Androgen Antagonists / Q000494:pharmacology; D000818:Animals; D001141:Aromatase / Q000378:metabolism; D047072:Aromatase Inhibitors; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology*; D013196:Dihydrotestosterone / Q000097:blood; D004343:Drug Implants; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000378:metabolism; D005260:Female; D008297:Male; D011944:Receptors, Androgen / Q000378:metabolism; D012098:Reproduction; D012621:Seasons; D020308:Songbirds / Q000502:physiology*; D013731:Territoriality; D013739:Testosterone / Q000008:administration & dosage / Q000097:blood / Q000502:physiology*; D014329:Tropical Climate; D014828:Vocalization, Animal
D000726:Androgen Antagonists; D047072:Aromatase Inhibitors; D004343:Drug Implants; D004791:Enzyme Inhibitors; D011944:Receptors, Androgen; D013196:Dihydrotestosterone; D013739:Testosterone; D004958:Estradiol; D001141:Aromatase