# Variation in Eusperm Length May Reflect Reproductive Barriers and Differences in Sperm Competition Intensity Among Littorina Snails

## TL;DR

Variation in sperm length among snail species and ecotypes may contribute to reproductive barriers and reflect differences in sperm competition.

## Contribution

The study explores how eusperm length variation in Littorina snails relates to reproductive isolation and sperm competition.

## Key findings

- Eusperm length differs between ecotypes, suggesting a role in prezygotic reproductive barriers.
- Species-level differences in eusperm length may reflect varying sperm competition intensities.

## Abstract

Reproductive barriers limit gene flow and drive population divergence. Sperm morphology plays an important role in reproductive barriers, as successful fertilization depends on how well sperm perform in the female environment. Specifically, sperm length must be adapted to fit the female reproductive tract and storage organs. We investigated sperm length in species and ecotypes of Littorina, a genus of promiscuous marine snails with internal fertilization. Various Littorina species have ecotypes adapted to different shoreline environments where reproductive traits like sperm length divergence might play a role in reinforcing these barriers. Due to their promiscuity, sperm competition likely plays a role in Littorina, and sperm length variation can give insights regarding sperm competition intensities. This study examined eusperm length in four species (L. fabalis,
L. littorea
,
L. obtusata
,
L. saxatilis
) and two different ecotypes in both L. fabalis and
L. saxatilis
. The ecotypes of both L. fabalis and
L. saxatilis
differed in eusperm lengths, indicating the potential for this trait to be involved in prezygotic reproductive barriers between ecotypes of these species. Among‐species differences in eusperm length variation were observed and may be a result of different sperm competition intensities.

Reproductive barriers, such as sperm morphology, play a key role in limiting gene flow and driving divergence in internally fertilizing species. We examined eusperm length variation in different Littorina species and ecotypes to assess its role in reproductive isolation and sperm competition. Eusperm length differed between ecotypes, suggesting its involvement in prezygotic barriers, whereas species and ecotype level differences may reflect varying sperm competition intensities.