Experimental evidence for antagonistic effects of sperm competition in two sea urchin species

Abstract of the paper "Experimental evidence for antagonistic effects of sperm competition in two sea urchin species": Sperm competition can occur when sperm from two or more males compete for fertilization of a batch of eggs. While it has been extensively studied in internal fertilizers, it remains poorly understood in external fertilizers. To investigate how sperm competition affects fertilization under sperm limitation, we conducted controlled experiments on two sea urchin species: Paracentrotus lividus and Dendraster excentricus. Eggs from a single female were exposed to sperm from three individual males separately (non-competitive treatment) or to a pooled sample from three males (competitive treatment). We measured fertilization success as proportion of eggs fertilized after two hours and assessed sperm motility as percentage of motile sperm and curvilinear velocity. For P. lividus, we estimated the sperm concentrations where fertilization success was 50% of maximum observed fertilization success (F₅₀), and the fertilization efficiency of the sperm (Fₑ), i.e. the likelihood that a sperm - egg encounter results in a fertilizing contact, using the fertilization kinetics model of Styan (1998). For D. excentricus, fertilization success was measured at a sperm concentration expected to produce 50% fertilization success. Sperm competition reduced fertilization success and increased F₅₀ compared to non-competitive treatments, suggesting antagonistic effects that may compromise fertilization under sperm-limited conditions in external fertilizers. Description of files: Code_Analysis: R-Code used for statistical analysis FeF50PL: Data on fertilization efficiency (Fe) and F50 used for analysis fertility_data_cleaned.csv: data on Dendraster excentricus fertilization success means for non-competitive- and sperm competition treatment; used for linear mixed-effects models and basic statistics fertility_data_cleaned.xlsx : see above Fertility_FHL_means.csv: used for plotting and calculate basic statistics Fertility_FHL_means.xlsx : see above fertility_vigo_cleaned.csv: data on Paracentrotus lividus fertilization success means for non-competitive- and sperm competition treatment; used for modelling F50 and Fe after Styan (1998), linear mixed-effects models and basic statistics fertility_vigo_cleaned.xlsx: see above Fertility_Vigo_means.csv: calculate statistics Fertility_Vigo_means.xlsx: see above FHL_FandF2.txt: look at differences between post 2h- and 24h fertilization success in D. excentricus motility_data_cleaned.csv : perm motility data on D. excentricus, used for linear-mixed effects models and basic statistics motility_data_cleaned.xlsx: see above Motility_Fertility_FHL_Means.csv: motility and fertilization data on D. excentricus, used to check if motility parameters affected fertilization success Motility_Fertility_FHL_Means.xlsx: see above Motility_Fertility_Vigo_Means.xlsx: : motility and fertilization data on P. lividus, used to check if motility parameters affected fertilization success Motility_Fertility_Vigo_Means.csv: see above Motility_Urchins.csv: used for plotting motility data in both sea urchin species motility_vigo_cleaned.csv: sperm motility data on P. lividus Size_Correlation_F.csv: test sizes and fertlilization success of both sea urchin species, to check if test size affects fertilzation success Size_Correlation_M.csv: test sizes and fertlilization success of both sea urchin species, to check if test size affects sperm motility Size_Correlation_M.xlsx: see above Code_Analysis.r: R-Code for statistical analysis