Data from: Long sperm fertilize more eggs in a bird

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.