Research reveals: Maternal hormones in birds have little influence!

Research reveals: Maternal hormones in birds have little influence!

A recent meta-analysis sheds light on the previously unclear evolutionary consequences of maternal hormones in bird eggs. Thirty years after their discovery, many questions remain unanswered. The research team Dr. Alfredo Sanchez-Tójar from Bielefeld University examined the effects of maternal hormones on the fitness of offspring and parents. The team analyzed 438 effect sizes from 57 studies on 19 wild bird species.

The aim of the study was to test a connection between higher levels of maternal hormones and fitness benefits. However, the results show a very weak and variable influence on the fitness measures. Neither the type of hormone nor the age of the birds nor methodological differences could adequately explain this variability.

Research approaches and challenges

The heterogeneity of the results could be influenced by phylogenetic differences and variation within studies. Dr. Sánchez-Tójar emphasizes the need for a more holistic approach to research. Future research should also examine context dependencies and alternative mechanisms of maternal effects.

Another important aspect is the active role of the embryos in processing maternal hormones. High variability in effects could be caused by environmental conditions as well as interactions of multiple maternal influences on the egg. To address these questions, robust approaches to standardize and validate hormone extraction methods are required.

The influence of sex hormones

In addition to the influence of maternal hormones in the breeding phase, species-specific seasonal song changes in songbirds are also of interest. These are influenced by sex hormones and differences in gene expression patterns in the song control system, such as forschung.mpg.de describes.

Sex hormones, particularly testosterone, play a crucial role in modifying specific neuronal circuits in the brains of songbirds. This has a direct impact on physiological, morphological and behavioral characteristics that influence reproductive success. Male canaries exhibit seasonally altered song that is regulated by testosterone, while female domesticated canaries do not normally sing but can develop song through testosterone treatments.

Long-term testosterone treatments also cause morphological changes, including volume increases in nuclei of the song control system. In addition, the expression of nerve growth factors such as BDNF, which are important for learning to sing, is hormone dependent.

The multitude of mechanisms and their species-specific differences require in-depth comparative studies of the genetic regulatory mechanisms in order to further deepen the understanding of the evolution of sex-specific behavior.