The effects of maternal testosterone on offspring traits and competitiveness in birds are widely studied. However, the fate of maternal testosterone during early embryonic development and its impact on offspring remain unclear. Wang et al. aimed to investigate two possibilities: either the rapid metabolism of maternal testosterone prevents it from reaching the embryos, leading to a potential conflict between the mother and offspring, or the metabolites facilitate the uptake of lipophilic testosterone from the yolk into the embryonic circulation, where they may function directly or convert back to testosterone.

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Rock pigeons. Credit shutterstock.

To test their hypotheses, isotope-labelled testosterone (T-[D5]) was injected into freshly laid rock pigeon eggs. Analysis of the concentration and distribution of T-[D5] and its labelled metabolites in egg fractions at days 2, 5 and 10 of incubation was performed using liquid chromatography combined with tandem mass spectrometry.

Despite the use of a supraphysiological dosage of testosterone injection, a rapid decrease in yolk testosterone was observed within two days. It was metabolised into androstenedione, conjugated testosterone, etiocholanolone and components which were unidentified (due to methodological limitations). Interestingly, these findings demonstrate that testosterone, androstenedione and conjugated testosterone, but not etiocholanolone, reached the embryo, including its brain. Additionally, they found no sex-specific metabolism, which helps explain why maternal testosterone does not affect sexual differentiation.

Overall, this study provides novel evidence supporting both stated hypotheses. Maternal testosterone undergoes rapid conversion by the embryo, with several metabolites reaching the developing offspring. This research sheds light on the intricate dynamics of maternal–offspring interactions and the potential mechanisms underlying the effects of maternal testosterone on offspring traits.

Read the full article in Journal of Endocrinology 258 e220299