Hormonal correlates of breeding behavior and pouch color in the Magnificent Frigatebird, Fregata magnificens.
It is well known that testosterone (T) influences the expression of the behavior and many sexual traits during reproduction in vertebrates. However, patterns of circulating concentrations of T vary tremendously across free-living populations. Here the profiles of plasma T levels in the Magnificent Frigatebird, Fregata magnificens, are presented during the courtship, incubation and chick rearing stages of breeding. In addition, the predicted interrelationship of T and the expression of a sexually selected trait, the red gular pouch of males is investigated. Plasma levels of corticosterone (Cort) are reported in relation to the demands of breeding conditions in colonies. Blood samples were obtained from 26 males and 32 females in the 1993-1994 breeding season and 41 courting males in 1997. Pouch color and size were also estimated in these males. As expected, T levels changed across the breeding stages: birds showed high levels of T during courtship and much lower circulating levels during incubation and chick rearing. Consistent with the expected effect of T, individual pouch color and size correlated with circulating levels of this hormone. In this highly dimorphic species no correlation was found between T and body condition or tail asymmetry. Cort, in contrast, did not change across the three reproductive stages.
Osorno
José Luis
JL
Departamento de Ecología Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de México, AP 70-275, México DF 04510, Mexico.
Núñez-de la-Mora
Alejandra
A
D'Alba
Liliana
L
Wingfield
John C
JC
D000818:Animals; D001717:Birds / Q000097:blood / Q000378:metabolism / Q000502:physiology*; D001947:Breeding; D003345:Corticosterone / Q000097:blood; D005260:Female; D008297:Male; D010858:Pigmentation / Q000502:physiology*; D011863:Radioimmunoassay; D012726:Sexual Behavior, Animal / Q000502:physiology*; D013739:Testosterone / Q000097:blood
D013739:Testosterone; D003345:Corticosterone