In 1993, H. Schwabl published in @PNASNews a seminal paper: “Yolk [as] a source of maternal testosterone for developing birds”
This was the first study proposing a link between maternal egg hormones and fitness.
Our preregistered #systematicreview & #metaanalysis in Ecology Letters synthesises 438 effects from 57 studies on 19 wild 
species to test if & how egg hormones relate to fitness
https://doi.org/10.1111/ele.70100
Data & Code https://github.com/ASanchez-Tojar/meta-analysis_egg_hormones_and_fitness
Pre-registration https://doi.org/10.17605/OSF.IO/KU47W
Our #metaanalysis tested the adaptive significance of egg hormones in birds by combining evidence published since 1993, mostly experiments (76% effects).
In short: regardless of hormone type, we found little evidence for an effect of egg hormones on fitness-related traits, but high heterogeneity.
We tested several biological and methodological hypotheses:
Offspring age Experiments vs Observational Experiments on eggs vs mothers Fitness proxy Etc.
However, they did not explain much heterogeneity.
Importantly, most heterogeneity was associated with phylogeny and within-study variation, with negligible differences among studies
That is, on average, studies didn't differ in what they found: Our results are generalizable (replicable) among studies
In the light of a recent article (https://doi.org/10.1186/s12915-024-02101-x), showing substantial heterogeneity among analysts.
We tested the robustness of our findings to several analytical decisions. Our results were consistent across.
Also, though evidence for small-study & decline effects is widespread (https://doi.org/10.1186/s12915-022-01485-y), we did NOT find clear evidence of #publicationbias in our dataset. Presumably thanks to our efforts to obtain nonreported results directly from authors.
Indeed, something hard to digest was that:
Complete data extraction was only possible for 22/57 included studies
20 additional studies were excluded due to preventable reporting issues
8 authors had lost the data FOREVER 
PLEASE, publish your data! #opendata
(and if you want to help spread the word about the importance of #OpenScience, join @sortee!)
Though we didn't find clear evidence for a relationship between egg hormones and fitness proxies, this does NOT mean hormones are unimportant
The high heterogeneity found suggests context dependency
We need more research and better reporting! 
Thank you to all the authors who replied to our emails 
Also to the Ecology Letters editors & reviewers for the most thoughtful criticism I’ve ever received during peer review. It’s not often that peer review makes a difference.
Thank you all
