Plasma Levels of Prolactin and Gonadotropins during the Reproductive Cycle of White-Crowned Sparrows (Zonotrichia leucophrys)

Abstract

Abstract Plasma concentrations of prolactin, LH, and FSH were measured in free-living pairs of Zonotrichia leucophrys pugetensis throughout the natural breeding season, and during a photoperiodically induced cycle of gonadal development and regression in both sexes of captive Z. l. gambelii under controlled conditions. In free-living male Z. l. pugetensis plasma levels of FSH, which correlate well with changes in testicular weight reported previously, are higher than in females. Although only females of this species incubate, maximal levels of prolactin are observed in both sexes during late incubation. This is consistent with observations in other avian species and suggestive of a role for prolactin in incubation and associated parental behavior. The temporal association of elevated FSH with high levels of prolactin in females may represent a mechanism for maturation of ovarian follicles for the next clutch in this race, which typically raises as many as 3 broods per season. In the laboratory study on Z. l. gambelii, prolactin secretion in both sexes appears to have been induced photoperiodically in the absence of other environmental stimuli associated with incubation. The time course and magnitude of plasma prolactin levels were similar in both sexes, although levels were considerably lower than values obtained from incubating birds during the field study. Plasma levels of LH and FSH in females increased rapidly in response to photostimulation and began to decline after one week, whereas in males the pattern of increase and decrease of both gonadotropins was more gradual.