Sperm competition, in which the ejaculates of multiple males compete to fertilize a female's ova, results in strong selection on sperm traits. Although sperm size and swimming velocity are known to independently affect fertilization success in certain species, exploring the relationship between sperm length, swimming velocity and fertilization success still remains a challenge. Here, we use the zebra finch (Taeniopygia guttata), where sperm size influences sperm swimming velocity, to determine the effect of sperm total length on fertilization success. Sperm competition experiments, in which pairs of males whose sperm differed only in length and swimming speed, revealed that males producing long sperm were more successful in terms of (i) the number of sperm reaching the ova and (ii) fertilizing those ova. Our results reveal that although sperm length is the main factor determining the outcome of sperm competition, complex interactions between male and female reproductive traits may also be important. The mechanisms underlying these interactions are poorly understood, but we suggest that differences in sperm storage and utilization by females may contribute to the outcome of sperm competition.
Sperm competition experimental data
The file contains the data collected during a sperm competition experiment conducted on captive bred zebra finches. Using a mate switching experimental design, we investigated whether sperm length (either long or short) influenced the number of sperm from each competing male that reached the ovum, and the number of embryos sired by each male.
Summary paternity
The file contains the summary paternity data for each individual trio of birds (one female and one pair of males) used in the sperm competition experiment. This file was required to calculate summary statistics for the manuscript.
Sperm length and competitive success
This R script contains the code that was used to carry out the statistical tests and summary data in the manuscript and for table S5 in the electronic supplementary material
Sperm quality comparison sperm competiton males
This data file contains the results of the sperm quality analyses carried out on all male zebra finches that were used in the sperm competition experiments. Data are arranged side by side for each pair of competing males, and analysed by comparing the sperm quality long and short sperm males, using a paired design.
sperm quality comparison sperm competiton males.txt
Testes mass sperm competition males
This file contains the left testes mass data from the males used in sperm competition experiment
Seminal glomera mass
This file contains the left and right seminal glomera mass data from a small number of male zebra finches producing either long or short sperm. These males were not used in the sperm competition experiments.
Copulation rate
This file contains the data from a study investigating whether male zebra finches with different sperm lengths (long or short) copulated with females at the same rate. These males were not used in the sperm competition experiments.
Sperm quality comparisons
This R script contains the code to investigate whether sperm quality varies with sperm length (long or short), and whether left testes mass is related to sperm length. Code is also provided for additional studies investigating whether sperm length is related to seminal glomera mass and copulation rate (not that these final two studies did not use the males from the sperm competition experiments. The results of all statistical tests were used to make tables S1 - S4 in electronic supplementary material 2.
Relatedness scores
This file contains the relatedness scores for all males and females used in the sperm competition experiments. Data were obtained from the detailed zebra finch pedigree and estimated using the R package Pedantics.
Relatedness scores_male x female_ male x male
The data file contains relatedness scores for the males and females arranged so the male x female and male x male mean scores can be calculated
Relatedness scores
This R script contains code to calculate the mean relatedness scores between pairs of males and females, and between the pairs of competing males.
relatedness scores.R