Yolk androgens reduce offspring survival

Keith W Sockman; Hubert Schwabl

doi:10.1098/rspb.2000.1163

Females may favour some offspring over others by differential deposition of yolk hormones. In American kestrels (Falco sparverius), we found that yolks of eggs laid late in the sequence of a clutch had more testosterone (T) and androstenedione (A4) than yolks of firstlaid eggs. To investigate the effects of these yolk androgens on nestling fitness, we injected both T and A4 into the yolks of firstlaid eggs and compared their hatching time, nestling growth and nestling survival with those of firstlaid eggs in which we injected vehicle as a control. Compared to controls, injection of T and A4 at a dose intended to increase their levels to those of laterlaid eggs delayed hatching and reduced nestling growth and survival rates. Yolk androgen treatment of egg 1 had no effect on survival of siblings hatching from subsequently laid eggs. The adverse actions of yolk androgen treatment in the kestrel are in contrast to the favourable actions of yolk T treatment found previously in canaries (Serinus canaria). Additional studies are necessary in order to determine whether the deposition of yolk androgens is an adaptive form of parental favouritism or an adverse byproduct of endocrine processes during egg formation. Despite its adaptive significance, such transgenerational effects of steroid hormones may have helped to evolutionarily shape the hormonal mechanisms regulating reproduction. Females may favour some offspring over others by differential deposition of yolk hormones. In American kestrels ( Falco sparverius ), we found that yolks of eggs laid late in the sequence of a clutch had more testosterone (T) and androstenedione (A 4 ) than yolks of firstlaid eggs. To investigate the effects of these yolk androgens on nestling fitness, we injected both T and A 4 into the yolks of firstlaid eggs and compared their hatching time, nestling growth and nestling survival with those of firstlaid eggs in which we injected vehicle as a control. Compared to controls, injection of T and A 4 at a dose intended to increase their levels to those of laterlaid eggs delayed hatching and reduced nestling growth and survival rates. Yolk androgen treatment of egg 1 had no effect on survival of siblings hatching from subsequently laid eggs. The adverse actions of yolk androgen treatment in the kestrel are in contrast to the favourable actions of yolk T treatment found previously in canaries ( Serinus canaria ). Additional studies are necessary in order to determine whether the deposition of yolk androgens is an adaptive form of parental favouritism or an adverse byproduct of endocrine processes during egg formation. Despite its adaptive significance, such transgenerational effects of steroid hormones may have helped to evolutionarily shape the hormonal mechanisms regulating reproduction.

Yolk androgens reduce offspring survival

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