Hermaphrodites have lower metabolic rates than gonochores

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-..., , 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

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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.

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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_cong...,