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

Abstract

SummarySocial competition among female birds has been shown to positively affect yolk androgen levels, perhaps providing a mechanism to communicate environmental conditions to offspring. Whether this relationship is due to social density or to differences among mothers that breed in different social situations is unclear. We manipulated breeding density to test these alternative explanations. Yolk androgens were measured in clutches of European starlings, Sturnus vulgaris, breeding in consecutive years in outdoor aviaries of different sizes and with varying numbers of breeding pairs. Testosterone (T) levels increased significantly with increasing density. Dihydrotestosterone (DHT) levels increased with the number of nest boxes available. The number of nest boxes monopolized by a breeding male negatively affected androstenedione (A4) levels, positively affected DHT levels and did not affect T levels. Other factors related to social interactions or competition among females (including polygyny) did not influence yolk hormone levels. Within-female yolk androgen levels were highly consistent over two consecutive years even though females were breeding in opposite breeding densities during each year, suggesting that individual characteristics are important determinants of variation in maternal androgen allocation in addition to potential effects of environmental conditions. This within-female consistency of yolk androgen levels across years has important implications.

Prenatal environmental effects match offspring begging to parental provisioning

“…Highly demanding offspring are the progeny of parents that experienced ready access to high-quality resources during this critical period, whereas more weakly begging young are produced by parents that were more food-deprived. Depending on their particular environmental circumstances, the same pair might therefore produce offspring of different behavioural types, although the extent to which the environment induces plasticity might vary among individuals (Eising et al 2008). Our measure of parental provisioning combines maternal and paternal care, so it is not possible for us to infer whether the correlation between parental behaviour and offspring begging differs between parents (as in the great tit: see Kö lliker et al 2000).…”

Evolutionary implications of interspecific variation in a maternal effect: a meta-analysis of yolk testosterone response to competition

“…The majority of studies examining intraspecific variation in avian maternal hormone allocation focus on the effects of competitive social interactions [7]. Most of these studies find a positive relationship between testosterone allocated to egg yolks and transient increases in competition, such as increased breeding density [12][13][14][15][16][17][18] or conspecific aggression [19][20][21][22][23]. Exposure to increased yolk testosterone typically increases nestling development (e.g.…”

Selection on personality in a songbird affects maternal hormone levels tuned to its effect on timing of reproduction

“…Although theory would also predict systematical and heritable variations within species, this has been overlooked. One study on starlings (Eising et al 2008) showed that androgen levels are characteristic of individual females, while another found an effect of selection on behavioural traits on yolk androgens (Gil & Faure 2007), suggesting such heritable variation.…”