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

Abstract

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 androgen 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 androstenedione (A4) and testosterone (T) and captured the females that laid these clutches for phenotypic measurements. Although average egg androgen 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 androgens. Within clutches, androgen 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 androgens than females in poor condition. Our results are consistent with the idea that differences in yolk androgen levels may be one mechanism underlying seasonal variation in reproductive success and it is possible that changes in egg androgen 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 androgen levels.

Maternal yolk androgens in European starlings: affected by social environment or individual traits of the mother?

“…Our results show that between-female differences are quite consistent over time and are only to some extent likely to be influenced by environmental challenges. Our repeatability estimates closely resemble the ones found for yolk A4 and T levels in a recent study by Tobler et al (2007) on Pied flycatchers Ficedula hypoleuca. Although their data describe hormone levels of successive clutches, laid within two weeks of each other during a single breeding season, not across two seasons as in our study, they also showed large inter-female variation in yolk androgen levels and a remarkable consistency within individual females.…”

Maternal transfer of androgens in eggs is affected by food supplementation but not by predation risk

“…An alternative prediction is that, if yolk androgen transfer is costly for the females, females receiving food supplementation should be able to transfer higher levels of hormones in the eggs. Th is seems unlikely in our study system, however, since in pied fl ycatchers females naturally in good condition seem to transfer lower levels of androgens in eggs (Tobler et al 2007). 2) We further predicted that the within-clutch hormone transfer pattern would be aff ected by food supplementation: fed females may allocate more androgens to the last egg to counteract hatching asynchrony, thus increasing the survival probability of the later hatched chicks.…”

Genetic differences in yolk testosterone levels influence maternal hormone deposition in the second laying cycle in Japanese quails

“…In particular, altricial birds can produce a distinct pattern of yolk androgen concentrations within a single clutch (Schwabl, 1993;Eising et al, 2001) as well as between successively laid clutches (Schwabl, 1997;Gil et al, 2006;Tobler et al, 2007). This between-clutch pattern of yolk androgen deposition was not investigated in free-living precocial birds yet but a decline of yolk testosterone (T) concentrations was found between the early and the latest stages of the first reproductive cycle in domestic species (Okuliarova et al, 2011a;Guibert et al, 2012).…”