At the same time, increasing evidence indicates that the embryo may not simply be a passive recipient of maternal signals 14, 15. So far, extensive studies have accumulated that enable us to understand the role of the mother and the effects of her hormones on the offspring in the post-natal stage. Such variation would boost the development of later-laid eggs at the cost of earlier-laid eggs under good food conditions, yet reduce the early survival of the later-laid eggs under poor food conditions which leads to brood size reduction 12, 13. A classic example, in birds, is the maternal transfer of androgens that vary (often increase) with the egg laying sequence in the same reproductive attempt 7. Over the past decades it has become increasingly clear that such effects occur already prenatally by exposing embryos or provisioning eggs differentially with both resources and signals such as nutrients, and hormones (e.g. Such transfer can depend on the maternal environment which provides the mother with a tool to adjust the developmental trajectory and final phenotype of their offspring to environmental fluctuations, contributing to fitness by so called adaptive anticipatory maternal effects 1. Mothers can affect the development of their offspring not only by transferring information via their genes, but also by transferring non-genetic signals such as nutrients, immune factors, and hormones. Our findings indicate that embryos have certain plasticity in response to maternal androgen levels depending on maternal signals.

We found that eggs with increased androgens show a different degree of androgen metabolism depending either on the egg laying sequence or initial androgen levels or both. We experimentally elevated androstenedione and testosterone levels in first eggs to that present in second eggs and measured the change in androgen levels and its main metabolites (etiocholanolone and conjugated testosterone) after 3.5 days of incubation. We used Rock pigeons ( Columba livia), that lay two egg clutches where maternal androgen levels in second laid eggs at oviposition are higher than in first laid eggs, and investigated the plasticity of embryonic metabolism of maternal androgens. However, whether embryos from different positions can be plastic in their response to the maternal signals, potentially leading to a mother–offspring conflict, is yet unclear. Mothers can differentially deposit their resources in the same reproductive attempt in relation to the offspring position in the sibling hierarchy. Mothers can influence offspring phenotypes by transferring non-genetic information to the young, which provides them with a flexible tool to adjust the developmental trajectory of the young in fluctuating environments.

Cabinet incubator