- Department of Ecology, SLU, Uppsala, Sweden
- Behaviour & Ethology, Demography, Evolutionary ecology, Life history, Maternal effects, Phenotypic plasticity, Population ecology, Statistical ecology
Preregistration - The effect of dominance rank on female reproductive success in social mammals
Why are dominant females not always showing higher reproductive success? A preregistration of a meta-analysis on social mammals
In social species conflicts among group members typically lead to the formation of dominance hierarchies with dominant individuals outcompeting other groups members and, in some extreme cases, suppressing reproduction of subordinates. It has therefore been typically assumed that dominant individuals have a higher breeding success than subordinates. However, previous work on mammals (mostly primates) revealed high variation, with some populations showing no evidence for a link between female dominance reproductive success, and a meta-analysis on primates suggests that the strength of this relationship is stronger for species with a longer lifespan . Therefore, there is now a need to understand 1) whether dominance and reproductive success are generally associated across social mammals (and beyond) and 2) which factors explains the variation in the strength (and possibly direction) of this relationship.
In their preregistration, Shivani et al.  plan to perform a meta-analysis on 86 social mammal species to address these two points. More specifically, they will investigate whether the relationship between female dominance and reproductive success vary according to life history traits (e.g. stronger for species with large litter size), ecological conditions (e.g. stronger when resources are limited) and the social environment (e.g. stronger for cooperative breeders than for plural breeders).
The two reviewers and I were particularly positive and enthusiastic about this preregistration and only had minor comments that were nicely addressed by the authors. We found the background well-grounded in the existing literature and that the predictions were therefore clear and well-motivated. The methods were particularly transparent with a nicely annotated R script and the authors even simulated a dataset with the same structure as the actual data in order to make sure that the coding of the data handling and statistical analyses were appropriate (without being tempted to look at model outputs from the true dataset).
Perhaps one limitation to keep in mind once we will have the chance to look at the outcome of this study if that the dataset may not be fully representative of social species with dominance hierarchies. For example, the current dataset contains only one aquatic mammal (Mirounga angustirostris) as far as I can see, which is likely due to a lack of knowledge on such systems. Furthermore, not only mammals exhibit dominance hierarchies and it will be interesting to see if the results of the proposed study hold for other social taxa (and if not, what may explain their differences).
That being said, the proposed study will already offer a much broader overview of the relationship between dominance and reproductive success in animal societies and a better understanding for its variation. The reviewers and I believe it will make an important contribution to the fields of socio-ecology and evolutionary ecology. I therefore strongly recommend this preregistration and we are particularly looking forward to seeing the outcome of this exciting study.
 Majolo, B., Lehmann, J., de Bortoli Vizioli, A., & Schino, G. (2012). Fitness‐related benefits of dominance in primates. American journal of physical anthropology, 147(4), 652-660. doi: 10.1002/ajpa.22031
 Shivani, Huchard, E., Lukas, D. (2020). Preregistration - The effect of dominance rank on female reproductive success in social mammals In principle acceptance by PCI Ecology of the version 1.2 on 07 July 2020. https://github.com/dieterlukas/FemaleDominanceReproductionMetaAnalysis/blob/trunk/PreregistrationMetaAnalysis_RankSuccess.Rmd
Investigating the rare behavior of male parental care in great-tailed grackles
Studying a rare behavior in a polygamous bird: male parental care in great-tailed grackles
The Great-tailed grackle (Quiscalus mexicanus) is a polygamous bird species that is originating from Central America and rapidly expanding its geographic range toward the North, and in which females were long thought to be the sole nest builders and caretakers of the young. In their pre-registration , Folsom and collaborators report repeated occurrences of male parental care and develop hypotheses aiming at better understanding the occurrence and the fitness consequences of this very rarely observed male behavior. They propose to assess if male parental care correlates with the circulating levels of several relevant hormones, increases offspring survival, is a local adaptation, and is a mating strategy, in surveying three populations located in Arizona (middle of the geographic range expansion), California (northern edge of the geographic range), and in Central America (core of the range). This study is part of a 5-year bigger project.
Both reviewers and I strongly value Folsom and collaborators’ commitment to program a study, in natural field conditions, of a rare, yet likely evolutionary-important behavior, namely parental care by males of the great-tailed grackle. Yet, we all also recognized that it is a risky endeavor, and as a consequence, we wondered about the authors’ ability to reach a sufficient sample size to statistically test (all) hypotheses and predictions with enough confidence (e.g. risk of type I errors, also known as false positives).
Folsom and collaborators acknowledged these limitations in their pre-registration. (i) They made the exploratory nature of their research work clear to readers. (ii) They adapted their analysis plan in running prior power analyses and in focusing on effect sizes (estimates and confidence intervals). (iii) Last and not least, Folsom and collaborators clearly exposed a priori hypotheses, their associated predictions and alternatives, and ranked the latter based on their plausibility according to knowledge in the current and other study systems. Developing theory about male parental care behavior more generally with regard to a polygamous species that is rapidly expanding its geographic range and that is considered not to provide male parental care is without any doubt an added value to this study.
In summary, while this study will likely be insufficient to fully understand male parental care behavior of great-tailed grackles, it is much needed because it will definitely allow rejecting some predictions (e.g., if this behavior is present in all the studied populations, it would be common across range against expectation; finding only one male providing care to an unrelated offspring would lead to reject the prediction that males only care for their own offspring) and thus it will help laying the foundation of future research directions.
I strongly support the pre-registration system and thank all the contributors for producing a fruitful discussion throughout the review process, which in fine improved the clarity and logic of this pre-registration. Given the positive and encouraging reviews, the detailed and thorough answers to all comments by Folsom and collaborators, and their satisfactory and interesting revisions, I am happy to recommend this pre-registration and I look forward to seeing its outcomes.
 Folsom MA, MacPherson M, Lukas D, McCune KB, Bergeron L, Bond A, Blackwell A, Rowney C, Logan CJ. 2020. Investigating the rare behavior of male parental care in great-tailed grackles. corinalogan.com/Preregistrations/gmalecare.html In principle acceptance by PCI Ecology of the version on 15 June 2020 corinalogan/grackles/blob/master/Files/Preregistrations/gmalecare.Rmd.