DOI: 10.5061/dryad.c866t1gdg
title: Sperm competition favours intermediate sperm size in a hermaphrodite

description: Sperm competition is a potent mechanism of post-copulatory sexual
 selection that has been found to shape reproductive morphologies and
 behaviours in promiscuous animals. Especially sperm size has been argued
 to evolve in response to sperm competition through its effect on sperm
 longevity, sperm motility, the ability to displace competing sperm and
 ultimately fertilization success. Additionally, sperm size has been
 observed to co-evolve with female reproductive morphology. Theoretical
 work predicts that sperm competition may select for longer sperm but may
 also favour shorter sperm if sperm size trades off with number. In this
 study, we studied the relationship between sperm size and post-mating
 success in the free-living flatworm, Macrostomum lignano. Specifically, we
 used inbred isolines of M. lignano that varied in sperm size to
 investigate how sperm size translated into the ability of worms to
 transfer and deposit sperm in a mating partner. Our results revealed a
 hump-shaped relationship with individuals producing sperm of intermediate
 size having highest sperm competitiveness. This finding broadens our
 understanding of the evolution of sperm morphology by providing empirical
 support for stabilizing selection on sperm size under sperm competition.
description: # **Sperm competition favours intermediate sperm size in a hermaphrodite**
 [https://doi.org/10.5061/dryad.c866t1gdg](https://doi.org/10.5061/dryad.c866t1gdg) ### Summary In this study, we investigate the relationship between variation in sperm size and sperm transfer success in a simultaneous hermaphrodite, *M. lignano.* Our results suggest stabilizing selection on sperm size under sperm competition.  ### Description of the data and file structure The results in the study were obtained from four separate datasets. Each dataset holds data used to obtain a section of the results presented in the study. \__________________________________________________________________________________________________________________________\_ "**bas1.csv**" has the sperm size measures of BAS1 worms "id" : specifying different individuals  "rep" : replicate sperm from each individual "Total", "Bristle", "Shaft", "Feeler", "Brush" : measurements of respective sperm morphological trait lengths (in 'µm') \___________________________________________________________________________________________________________________________\_ "**lm.csv**" has the sperm size measures of LM line worms "line" : LM line identity "id" :  IDs of individuals blind to LM line identity "ind" : identity of individuals within each LM line "rep" : replicate sperm from each individual "Total", "Body", "Bristle", "Shaft", "Feeler", "Brush" : measurements of respective sperm morphological trait lengths (in 'µm') \____________________________________________________________________________________________________________________________\_ "sts.csv" has sperm transfer success data from the mating experiments. As described in the methods, the sperm size (and PC1&2) values in this sheet are mean values of LM lines. Mean standard deviation (_sd) and coefficients of variation (_cv) are included as well. "id" :  IDs of individuals blind to LM line identity "line" : LM line identity "tot" : Total number of sperm counted in the antrum of all partners "gfp" : Number of GFP+ sperm in the antrum of all partners "prop" : Proportion of GFP+ sperm among the total number of sperm "part" : number of partners from whom the number of sperm were counted "Total", "Body", "Bristle", "Shaft", "Feeler", "Brush": respective mean values of sperm morphological trait lengths in each LM line (in 'µm') "Total_sd", "Body_sd", "Bristle_sd", "Shaft_sd", "Feeler_sd", "Brush_sd" : respective standard deviations of sperm morphological trait lengths in each LM line (in 'µm') "Shape" : IDs used to assign shapes to datapoints in Figure 3 \_____________________________________________________________________________________________________________________________\_ "**rep.csv**" has data from repeated measures of same sperm cell, defined by the ID column. "rep" : replicate measures of each sperm cell "Total", "Bristle", "Shaft", "Feeler", "Brush" : repeated measurements of respective sperm morphological trait lengths (in 'µm') \_______________________________________________________________________________________________________________________________\_ "Datasets_Excel.xlsx" contains all the datasets as separate sheets in an excel file. ### Images and Videos Images 1-5 show sperm cells of *M. lignano* at 1000x magnification used to measure morphological traits. Video 1 shows sperm in female antrum observed under differential interference contrast illumination. Video 2 shows GFP+ sperm in the female antrum observed under epifluorescence illumination. ### Code/Software All analysis were performed in R (V4.2.3) and the R script used is provided here (Filename: R code \_ M. lignano). ### License Information Anyone can share this material, provided it remains unaltered in any way, this is not done for commercial purposes, and the original authors are credited and cited.