Most plants and many animals are hermaphroditic; whether the same forces are responsible for hermaphroditism in both groups is unclear. The well-established drivers of hermaphroditism in plants (e.g., seed dispersal potential, pollination mode) have analogues in animals (e.g., larval dispersal potential, fertilization mode), allowing us to test the generality of the proposed drivers of hermaphroditism across both groups. Here, we test these theories for 1153 species of marine invertebrates, from 3 phyla. Species with either internal fertilization, restricted offspring dispersal, or small body sizes are more likely to be hermaphroditic than species that are external fertilizers, planktonic developers, or larger. Plants and animals show different biogeographical patterns, however: animals are less likely to be hermaphroditic at higher latitudes – the opposite to the trend in plants. Overall, our results indicate that similar forces, namely competition amongst offspring or gametes, shape the evolution of hermaphroditism across the tree of life.

Data for many of the species in our dataset came from previously published meta-analyses on various marine invertebrate life-history traits (e.g., Marshall et al. 2012, Monro & Marshall 2015), supplemented with additional data on hermaphroditism and body size from the literature. Data were compiled in Microsoft Excel and phylogenetic logistic regressions testing the covariance between hermaphroditism and life-history/latitude were analyzed with the ‘phylolm’ package v. 2.6.2 (Ho and Ané 2014) in RStudio v.4.1717 (R Core Team 2021).

We extracted our phylogenies from the Open Tree of Life (Hinchliff et al. 2015) with the package ‘rotl’ v. 3.0.11 (Michonneau et al. 2016) and constructed phylogenetic trees with the package ‘phytools’ v. 0.7-80 (Revell 2012). Branch lengths for the phylogeny were unknown, so we scaled branch lengths using Grafen’s method (Grafen 1989) in the ‘ape’ package v. 5.6-1 (Paradis and Schliep 2019)

Literature Cited

• Grafen, A. 1989. The phylogenetic regression. Philos. Trans. R. Soc. Lond. B. Biol. Sci. 326:119–157.
• Hinchliff, C., S. Smith, J. Allman, J. G. Burleigh, R. Chaudhary, L. Cognill, K. Crandall, J. Deng, B. Drew, R. Gazis, K. Gude, D. Hibbett, L. Katz, H. D. Laughinghouse IV, E. J. McTavish, P. Midford, C. Owen, R. Ree, J. Rees, D. Soltis, T. Williams, and K. A. Cranston. 2015. Synthesis of phylogeny and taxonomy into a comprehensive tree of life. Proc. Natl. Acad. Sci. 112:12764–12769.
• Ho, L. S. T., and C. Ané. 2014. A linear-time algorithm for gaussian and non-gaussian trait evolution models. Syst. Biol. 63:397–408.
• Marshall, D. J., P. J. Krug, E. K. Kupriyanova, M. Byrne, and R. B. Emlet. 2012. The biogeography of marine invertebrate life histories. Annu. Rev. Ecol. Evol. Syst. 43:97–114.
• Michonneau, F., J. W. Brown, and D. J. Winter. 2016. rotl: an R package to interact with the Open Tree of Life data. Methods Ecol. Evol. 7:1476–1481.
• Monro, K., and D. J. Marshall. 2015. The biogeography of fertilization mode in the sea. Glob. Ecol. Biogeogr. 24:1499–1509.
• Paradis, E., and K. Schliep. 2019. ape 5.0: an environment for modern phylogenetics and evolutionary analyses in R. Bioinformatics 35:526–528.
• R Core Team 2021. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL https://www.R-project.org/.
• Revell, L. J. 2012. phytools: An R package for phylogenetic comparative biology (and other things). Methods Ecol. Evol. 3:217–223.

Programs/software required to open/analyze the data files:

• Microsoft Excel (view raw data and metadata, .csv files for analyses)
• Adobe Reader (view PDF's of phylogenetic trees)
• RStudio (open files, manipulate and analyze data)