Maternal hormones can have substantial phenotypic effects in the progeny of many vertebrates. It has been proposed that mothers adaptively adjust hormone levels experienced by particular young to optimize their reproductive output. In birds, systematic variation in egg hormone levels has been related to different female reproductive strategies. Because in many bird species prospects of the offspring change seasonally and with brood number, strategic adjustment of yolk @entity342 levels would be expected. To test this idea, we induced pied flycatcher (Ficedula hypoleuca) females to nest twice during the same season by removing their first clutches shortly after clutch completion. We collected eggs of first and replacement clutches to measure yolk concentrations of @entity2671 (A4) and @entity251 (T) and captured the females that laid these clutches for phenotypic measurements. Although average egg @entity342 levels were remarkably consistent within females, hormone patterns differed considerably between first and replacement clutches. Eggs of replacement clutches were heavier with larger yolks compared to first clutches, but they contained on average lower levels of @entity3800 . Within clutches, @entity342 concentration increased over the laying sequence in the first clutch, but decreased or remained more constant over the laying sequence in the replacement clutch. Mean yolk T, but not A4 levels, were negatively associated with laying date for both breeding attempts. Moreover, females in good body condition produced eggs containing lower levels of @entity3800 than females in poor condition. Our results are consistent with the idea that differences in yolk @entity342 levels may be one mechanism underlying seasonal variation in reproductive success and it is possible that changes in egg @entity342 patterns may reflect a change in female reproductive strategy. High within-female consistency also highlights the possibility that there may be some underlying genetic variation in yolk @entity342 levels.

Maternal XXXX in the pied flycatcher: timing of breeding and within-female consistency.

@entity3800 :: ('MESH:D000728', 'Chemical') :: ['androgens'] @entity251 :: ('MESH:D013739', 'Chemical') :: ['testosterone'] @entity2671 :: ('MESH:D000735', 'Chemical') :: ['androstenedione'] @entity342 :: ('CHEBI:50113', 'Chemical') :: ['androgen']
@entity3800 :: (MESH:D000728,Chemical) :: ['androgens']
