Sperm competition favours intermediate sperm size in a hermaphrodite

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 relatio..., , , # **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.

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\"**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...