Data from: Morphology-function relationships and repeatability in the sperm of Passer sparrows

Sperm performance is likely to be an important determinant of male
reproductive success, especially when females copulate with multiple
males. Understanding sperm performance is therefore crucial to fully
understand the evolution of male reproductive strategies. In this study,
we examined the repeatability of sperm morphology and motility measures
over three breeding seasons, and we studied relationships between sperm
morphology and function. We conducted this study in wild-derived captive
house sparrows (Passer domesticus) and Spanish sparrows (P.
hispaniolensis). Results for the two species were similar. As predicted
from results in other passerine species, total sperm length was highly
repeatable across ejaculates, and repeatability for the length of other
components was moderate. The repeatability of sperm swimming speed across
ejaculates was lower, but statistically significant, suggesting that sperm
velocity may be a relatively dynamic trait. Surprisingly, swimming speed
did not correlate with the relative length of the midpiece, and it
correlated negatively with the relative length of the flagellum and with
total sperm length. This pattern is the opposite of what theory predicts
and differs from what has been found in house sparrows before. Also
contrary to previous work, we found no evidence that total sperm length
correlates with sperm longevity. These results therefore highlight the
need for a better understanding of relationships between sperm morphology
and function in passerine birds.