Regulation of yolk-androgen concentrations by plasma prolactin in the American kestrel.
The concentrations of maternally derived androgens in the yolks of avian eggs vary within and among clutches, but a mechanistic basis for this variation has not been elucidated. We investigated in the American kestrel, Falco sparverius, whether changes in plasma-prolactin concentrations induced by changes in photoperiod and food supply affect yolk-androgen concentrations. Over the course of a photoinduced breeding period in the laboratory, we measured concentrations of plasma immunoreactive prolactin (ir-prolactin) in female kestrels with ad libitum food availability (control) or food availability that was reduced during the early breeding period. In a second laboratory study, we administered via osmotic mini-pumps ovine prolactin (o-prolactin) to females beginning on the day they laid their first egg of a clutch (egg-day 1) to determine the effects of high prolactin concentrations on yolk-androgen concentrations. In both this study and one on free-living kestrels, we quantified changes in yolk-androgen concentrations with date of clutch initiation. Concentrations of ir-prolactin in nonlaying females rose with date, irrespective of food treatment. Egg-day 1 ir-prolactin concentrations were higher in control females laying late during the breeding phase than in those laying early. This increase was absent in food-reduced females. Yolk-androgen concentrations in eggs 3 and 4 but not eggs 1 and 2 of the clutch were higher in clutches initiated late than in clutches initiated early in the breeding phase in both the field and laboratory. o-prolactin treatment elevated yolk-testosterone but not androstenedione concentrations. These findings suggest that, in American kestrels, seasonal and laying-associated increases in plasma-prolactin concentrations elevate yolk-testosterone concentrations. Food availability and other factors may interact with date to regulate the effects of prolactin on yolk-testosterone deposition.
Sockman
K W
KW
School of Biological Sciences, Center for Reproductive Biology, Washington State University, Pullman, Washington 99164-4236, USA. sockman@jhu.edu
Schwabl
H
H
Sharp
P J
PJ
D000728:Androgens / Q000378:metabolism*; D000818:Animals; D004530:Egg Yolk / Q000378:metabolism*; D005260:Female; D008297:Male; D010058:Oviposition / Q000502:physiology*; D011388:Prolactin / Q000502:physiology*; D020304:Raptors / Q000502:physiology*; D012621:Seasons; D012733:Sex Differentiation / Q000502:physiology*
D000728:Androgens; D011388:Prolactin