DOI: 10.5061/dryad.3r2280gt8
title: Sex-role-reversal and the Bateman gradient in coucals – females benefit from mating with multiple partners

description: Conventional sex roles imply that males compete more vigorously with each
 other for fertilizations, whereas females are more selective in choosing a
 mate. As a consequence, mating and reproductive success is typically more
 variable in males (Bateman’s principles). However, Charles Darwin already
 mused that some species may defy these principles, resulting in stronger
 sexual selection in females than males, but empirical evidence has been
 mixed. We studied the potential for sexual selection in two sympatric
 coucals – a bird family with high sex-role-variability. In
 sex-role-reversed black coucals, females compete for territories while
 males provide parental care. In white-browed coucals, sex roles are
 flexible. Females of both species had steeper Bateman gradients than
 males, suggesting females benefit from multiple mating. Male black coucals
 benefitted from sneaking copulations with their social mate while she
 prepared clutches for other mates – a male strategy not conceptually
 included in Bateman’s principles that focuses on the number of mating
 partners, but not on increasing reproductive success by repeatedly mating
 with the same partner. Our findings support reversed Bateman’s principles,
 with females having a higher potential for sexual selection than males.
 Sex-role-flexibility allows females to secure additional mates and
 emancipate themselves from parental care, and it allows males to invest in
 parental care and emancipate themselves from pre-copulatory competition.
description: # Sex-role-reversal and the Bateman gradient in coucals – females benefit
 from mating with multiple partners For correspondence regarding the code
 and statistical analyses, please contact: Guadalupe
 ([lopez-nava.guadalupe@bi.mpg.de](mailto:lopez-nava.guadalupe@bi.mpg.de))
 For correspondence regarding the data collection, statistical analyses,
 and study systems, please contact: Wolfgang
 ([wgoymann@bi.mpg.de](mailto:wgoymann@bi.mpg.de)) In this repository, you
 can find all the data and code needed to reproduce our study on Bateman
 Gradients in Black coucals (*Centropus grillii*) and White-browed coucals
 (*Centropus superciliosus*) inhabiting the Usangu wetlands of Tanzania.
 Our study is based on data collected over **15 breeding seasons** for
 Black coucals and **13 breeding seasons** for White-browed coucals. ####
 Github Repository Contents *
 [`BatemangradientsCoucals.Rproj`](https://github.com/lguadal/Batemangradients_coucals/blob/main/BatemangradientsCoucals.Rproj) RStudio project to run and reproduce results. *Notes*: 1. All analyses in Rmarkdown scripts are referenced according to their number in the manuscript. 2. Tables were created using the R package [gt v.0.2.2](https://cran.r-project.org/web/packages/gt/index.html). 3. Figures were created using the R package [ggplot2 v.3.3.3](https://cran.r-project.org/web/packages/ggplot2/index.html). #### Dryad Repository Contents ##### Black coucals * `GradientsBC.Rmd` R Markdown script containing the statistical analyses. Outputs of estimates of 1) Bateman gradients, 2) differences between sex classes, 3) selection opportunities, and 4) path selection analyses for age. * `PathsSelection_BC.Rmd` R Markdown script containing the path selection analyses of morphological traits. ##### White-browed coucals * `GradientsWB.Rmd` R Markdown script containing the statistical analyses. Outputs of estimates of 1) Bateman gradients, 2) differences between sex classes, and 3) selection opportunities. * `PathSelection_WB.Rmd` R Markdown script containing the path selection analyses of morphological traits. ### Datasets description: * For each provided data set, we include details on the variables presented. Each row contains the associated information of an individual bird. * Standardized values of mating and reproductive success are generated directly through the analysis in the Rmarkdown scripts. #### `blackcoucal_gradients.csv` | Column name | Type | Units / Scale | Description | | --------------- | ------- | ------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------- | | `ring_no_lab` | factor | categorical (299 levels) | An anonymized identifier for each individual bird obtained from sibship analyses. | | `year` | factor | categorical (2001–2019) | Year when the bird was sampled. | | `ring_no` | factor | categorical (167 levels) | Ring number identifying each bird. | | `sex` | factor | categorical (`female`, `male`) | Sex of the individual. | | `age` | factor | categorical (1, 2, 3) | Age class of the individual (in years) | | `totaloff` | numeric | count | Total number of genetic offspring sired by the individual during a breeding season. | | `totalmates` | numeric | count | Total number of genetic mates of an individual during a breeding season. | | `epy` | factor | categorical (0, 1) | Extra-pair offspring indicator (1 = extra-pair offspring present, 0 = none). | | `category` | factor | categorical ("1females", "2males"", "3malesENO"") | Classification category of the individual (2males == males without extra nest offspring (ENO); 3malesENO == males with ENO). | | `totalnest_sum` | numeric | count | Total number of nests where an individual sired genetic offspring. | #### `data_morpho_BC.csv` | Column name | Type | Units / Scale | Description | | ------------------- | ------- | ------------------------------------ | ---------------------------------------------------------------------------------------------------------------------------- | | `ring_no` | factor | categorical (163 levels) | Ring number identifying each bird. | | `sex` | factor | categorical (`female`, `male`) | Sex of the individual. | | `year` | factor | categorical (2001–2014) | Year when the bird was sampled. | | `parent` | factor | categorical (163 levels) | An anonymized identifier for each individual bird obtained from sibship analyses. | | `totaloff` | numeric | count | Total number of genetic offspring produced by the individual during a breeding season. | | `totalmates` | numeric | count | Total number of genetic mates of an individual during a breeding season. | | `epy` | factor | category (0/1) | Presence of an extra-pair young in the total of genetic offspring sired by an individual. | | `category` | factor | categorical (1females, 2males, etc.) | Classification category of the individual (2males == males without extra nest offspring (ENO); 3malesENO == males with ENO). | | `species` | factor | categorical (1 level: black coucal) | Species of the bird. | | `body_mass` | numeric | g | Body mass of the individual. Some entries missing. | | `right_tarsus` | numeric | mm | Length of the right tarsus. | | `tarsus_mean_SMI` | numeric | mm | Mean tarsus length used for scaled mass index calculations. | | `scaled_mass_index` | numeric | - | Scaled mass index for body condition. | | `tail_body` | numeric | mm | Tail-to-body length measurement. | #### `whitebrowedcoucal_gradients.csv` | Column name | Type | Units / Scale | Description | | ----------- | ------- | ------------------------------ | ----------------------------------------------------------------------------------- | | `lab_id` | factor | categorical (162 levels) | Laboratory ID for each individual bird. | | `year` | factor | categorical (2005–2019) | Year when the bird was sampled. | | `no_off` | numeric | count | Total number of genetic offspring sired by the individual during a breeding season. | | `no_mates` | numeric | count | Total number of genetic mates of an individual during a breeding season. | | `sex` | factor | categorical (`female`, `male`) | Sex of the individual. | | `ring_no` | factor | categorical (100 levels) | Ring number identifying each bird. | #### `data_morpho_WB.csv` | Column name | Type | Units / Scale | Description | | ------------------- | ------- | ------------------------------------------ | -------------------------------------------------------------------------------------- | | `ring_no` | factor | categorical (96 levels) | Ring number identifying each individual bird. | | `sex` | factor | categorical (`female`, `male`) | Sex of the individual. | | `year` | factor | categorical (2005–2017) | Year when the bird was sampled. | | `lab_id` | factor | categorical (96 levels) | An anonymized identifier for each individual bird obtained from sibship analyses. | | `no_off` | numeric | count | Total number of genetic offspring produced by the individual during a breeding season. | | `no_mates` | numeric | count | Total number of genetic mates of an individual during a breeding season. | | `species` | factor | categorical (1 level: white-browed coucal) | Species of the bird. | | `body_mass` | integer | g | Body mass of the individual. | | `right_tarsus` | numeric | mm | Length of the right tarsus. | | `tarsus_mean_SMI` | numeric | mm | Mean tarsus length used for scaled mass index calculations. | | `scaled_mass_index` | numeric | - | Scaled mass index for body condition. | | `tail_body` | numeric | mm | Tail-to-body length measurement. | Coded by Guadalupe Lopez-Nava (2025)