Variation in eusperm length may reflect reproductive barriers and differences in sperm competition intensity among <i>Littorina</i> snails

<b>Abstract of the journal article "</b><b>Variation in eusperm length may reflect reproductive barriers and differences in sperm competition intensity among </b><b><i>Littorina</i></b><b> snails"</b>Reproductive barriers limit gene flow and drive population divergence. For internal fertilizers, 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. In species where sperm competition occurs, i.e. where multiple males compete to fertilize a female’s eggs, selection pressure can favor an optimal sperm length, reducing variation over time. Additionally, variation in sperm length may result in different optima in locally adapted populations or ecotypes that may facilitate further divergence. We investigated sperm length in species and ecotypes of <i>Littorina</i>, a genus ofpromiscuous marine snails with internal fertilization. Various <i>Littorina</i> species mate inter-specifically, where sperm length differences might prevent hybridization across species borders. Additionally, several <i>Littorina</i> species have ecotypes adapted to different shoreline environments where reproductive barriers like sperm length divergence might play a role inreinforcing these barriers. Due to their promiscuity, sperm competition probably plays a role in <i>Littorina</i>, and sperm length variation can give insights in sperm competition intensities. <i>Littorina</i> snails have two types of sperm, eusperm which is the fertilizing sperm, and parasperm. This study examined eusperm length in four species (<i>L. fabalis</i>, <i>L. littorea</i>, <i>L. obtusata</i>, <i>L. saxatilis</i>), and two different ecotypes in both <i>L. fabalis</i> and <i>L. saxatilis</i>. The ecotypes of both <i>L. fabalis</i> and <i>L. saxatilis</i> differed in eusperm lengths, suggesting that this trait may 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.<b>Description of attached data:</b>Code_Analysis.r: R-Code for the data analysis for the paper "Variation in eusperm length may reflect reproductive barriers and differences in sperm competition intensity among<i> </i><i>Littorina</i> snails". It enables the used to analyse eusperm length differences between groups and plot the eusperm length of the different groups. It also enables the user to analyse and plot the relationship between eusperm length and aperture perimeter in snails. The code can be used to analyse repeatability of the data, i.e. estimate the measurement error. It also can be used to calculate summary statistics on eusperm length and aperture perimeter in snails. Also, it can be used to conduct assumptions checks for further statistical analysis. Those analysis are also provided.Correlation_Eusperm_Aperture_LF.xlsx: mean eusperm length and aperture perimeter in<i> </i><i>Littorina fabalis</i> (dwarf and large ecotype) and<i> </i><i>Littorina obtusata. </i>The mean was calculated based on all eusperm length and aperture perimeter measurements taken in the mentioned species and ecotypes. Data on sampling location, time, and individual code are also included. Correlation_Eusperm_Aperture_LL.xlsx: mean eusperm length and aperture perimeter in<i> </i><i>Littorina </i><i>l</i><i>ittorea. </i>The mean was calculated based on all eusperm length and aperture perimeter measurements taken in the mentioned species and ecotypes. Data on sampling location, time, and individual code are also included. Correlation_Eusperm_Aperture_LS.xlsx: mean eusperm length and aperture perimeter in<i> </i><i>Littorina </i><i>saxatilis</i> (wave and crab ecotype). The mean was calculated based on all eusperm length and aperture perimeter measurements taken in the mentioned species and ecotypes. Data on sampling location, time, and individual code are also included. Individual_Eusperm_Lenghts.xlsx: individual eusperm length per individuum measured in<i> </i><i>Littorina fabalis</i> (dwarf and large ecotype)<i>, Littorina littorea, Littorina obtusata, Littorina saxatilis</i> (wave and crab ecotype). Data on sampling location, time, and individual code are also included. Repeatability.xls: eusperm length measured in triplicate in five males per species and ecotype; this is to calculate the measurement error, i.e. how much variation is due to biological vs. measurement variation<br>MANIFEST.txt contains the name and size of the attached files and README.txt the metadata.<b>Abbreviations:</b>LSC (<i>Littorina saxatilis</i> crab), LSW (<i>Littorina saxatilis</i> wave), LFD (<i>Littorina fabalis</i> dwarf), LFL (<i>Littorina fabalis</i> large), LO (<i>Littorina obtusata</i>), LL (<i>Littorina littorea</i>)