DOI: 10.5061/dryad.j3tx95xt4
title: Hermaphrodites have lower metabolic rates than gonochores

description: Hermaphroditism, where an individual can reproduce as both male and
 female, offers some clear reproductive advantages. Simultaneous
 hermaphroditism guarantees that every mature adult can mate with another –
 a particular advantage when opportunities to mate are scarce. Despite this
 potential benefit, hermaphroditism is relatively rare in animals. This
 paradox has long involved an energetics argument: hermaphrodites require
 more energy to fuel two reproductive roles instead of only one, which
 favours the evolution of separate sexes. However, this argument has never
 been tested. Here, we compare resting metabolic rates between
 hermaphrodites and gonochores across 536 species of marine invertebrates,
 spanning 11 phyla. Our analyses, which control for body size,
 environmental temperature, motility, and phylogeny, contradict predictions
 from classic theory: instead of requiring more energy than gonochores,
 hermaphrodites require ~27% less energy on average. These findings
 overturn a 150-year-old argument that hermaphroditism is rarer in animals
 because it is more costly, and highlight the need to reconsider the role
 of energetics in the evolution of sexual systems.
description: Description: Explanation of data files and instructions for analyses from
 'Hermaphrodites have lower metabolic rates than gonochores’ Author:
 George C. Jarvis Date: Friday 17 October 2025 --- 1. General note: These
 data were set up for analyses in R. Specifically, files were organized so
 that readers could download the zip folder
 (‘JarvisMarshall_mr_herm_data_code.zip’), unzip it, open the R project
 folder (‘mr_herm.Rproj’), and reproduce all of the analyses and figures
 from the project folder (‘JarvisMarshall_mr_herm_data_code’) as their
 working directory. The code should run fine on both Mac and PC computers
 (I originally ran this on a PC), but feel free to email me at gjarvis [at]
 uchicago.edu if you have any questions or issues running the script. ---
 1. Notes on subfolders within unzipped folder
 ‘JarvisMarshall_mr_herm_data_code’: 2a) ‘data_and_tree’ – contains the
 files for raw data (mr_herm_data_v10.xlsx) and phylogenetic tree
 (herm_tree_congruified_536_spp.nwk [Newick file]) for analyses and
 figures. 2b) ‘functions’ – contains .R scripts for functions used in the
 analyses. 2c) ‘scripts’ – contains the R notebook file to analyze the data
 and generate the figures in the MS ('herm_code_v4.Rmd'). 2d)
 'figures' - folder where figures from will be exported to. Note
 that for some figures, I uploaded them into Powerpoint, and edited them
 there. --- 1. Notes on files within ‘data_and_tree’ subfolder: 3a) Raw
 data are located in file 'mr_herm_data_v10.xlsx' within the
 sheet 'raw_data'. "NA's" represent missing data
 (e.g., in cases where there is no resolved taxonomic level for
 'order' for a species) or cases that are not applicable (e.g.,
 the type of hermaphroditism for species that have separate sexes:
 'herm_type_sim_seq' = 'NA'). Explanations for column
 headings in the raw data sheet, and the references for raw data are
 located in the 'metadata' and 'reference list' sheets,
 respectively. NOTE: I used the "raw_data" sheet in this .xlsx
 file to run all analyses and generate all figures for the MS. 3b)
 I've also included .csv files for each of the 3 sheets in the .xlsx
 file mentioned above: 'mr_herm_raw_data_v3.csv' (raw phenotypic
 data); 'mr_herm_phylum_comparison_v3.csv' (data comparing
 species distributions between our dataset and that of the World Register
 of Marine Species [WoRMS]); 'mr_herm_metadata_v3.csv' (metadata,
 describing column headings in the 'mr_herm_raw_data_v3.csv' and
 'mr_herm_phylum_comparison_v3.csv' files);
 'mr_herm_raw_data_v3.csv' (raw phenotypic data) and
 'mr_herm_data_references_v3.csv'. These files are in the folder
 'xlsx file as separate csv files', within the
 'data_and_tree' folder. 3b) The phylogenetic tree
 ('herm_tree_congruified_536_spp.nwk') has already been
 time-calibrated with the 'congruify.phylo' function in the
 package 'geiger' v. 2.0.11. For more information on this
 process, see: Eastman JM, Harmon LJ, Tank DC. 2013 Congruification:
 Support for time scaling large phylogenetic trees. Methods Ecol. Evol. 4,
 688–691. ([doi:10.1111/2041-210X.12051](doi:10.1111/2041-210X.12051)) ---
 1. Steps to reproduce analyses and figures: 4a) Open the R project file
 (‘mr_herm.Rproj’) project file within the unzipped
 ‘JarvisMarshall_mr_herm_data_code’ folder. 4b) Within the R project, open
 the .Rmd file, ‘herm_code_v4.Rmd’. The code should run fine from there.
 4c) I included the output figures in the 'figures' folder. ---
 1. General notes on R notebook file: 5a) The names of the files are as
 they appear in the .Rmd file ('herm_code_v4.Rmd'). In other
 words, if you change the name of a file (e.g., raw data, function) you
 will need to correspondingly change the names of the file as they are
 called in the .Rmd file. 5b) There are some packages that I had to
 download manually in the R console (e.g., package
 'ggtreeExtra'). In those cases, I left instructions for how to
 download the packages in the .Rmd file.