Data from: Effects of female-specific selection for reproductive investment on male fertility traits

Despite sharing an autosomal genome, the often divergent reproductive
strategies of males and females cause selection to act in a sex-specific
manner. Selection acting on one sex can have negative, positive, or
neutral fitness consequences on the opposite sex. Here we test how
female-limited selection on reproductive investment in Japanese quail
(Coturnix japonica) affects male fertility-related traits. Despite there
being no difference in the size of males’ testes from lines selected for
high female reproductive investment (H-line) or low female reproductive
investment (L-line), in both lines, the left testis had a greater volume
of sperm-producing tissue. Since H-line females have a larger left-side
restricted oviduct, this suggests a positive genetic correlation between
male and female gonad function, and that internal testis structure is a
target of sexual selection. However, despite H-line males having
previously been found to have greater fertilisation success in a
competitive scenario, we found little evidence of a difference between the
lines in sperm number, motility, velocity, length, or the number of sperm
that reached the ova. Pre-copulatory cues and/or the role of seminal fluid
in sperm motility may thus be more likely to contribute to the H-line male
fertilisation advantage in this species.