Sperm of more colorful males are better adapted to ovarian fluids in
lake char (Salmonidae)
Abstract
Fish often spawn eggs with ovarian fluids that have been hypothesized to
support sperm of some males over others (cryptic female choice).
Alternatively, sperm reactions to ovarian fluids could reveal male
strategies. We used wild-caught lake char (Salvelinus umbla) to
experimentally test whether sperm react differently to the presence of
ovarian fluid, depending on male breeding coloration, male inbreeding
coefficients (based of 4,150 SNPs), or the kinship coefficients between
males and females. Male coloration was positively linked to body size
and current health (based on lymphocytosis and thrombocytosis) but was a
poor predictor of inbreeding or kinship coefficients. We found that
sperm of more colorful males were faster in diluted ovarian fluids than
in water only, while sperm of paler males were faster in water than in
ovarian fluids. We then let equal numbers of sperm compete for
fertilizations in the presence or absence of ovarian fluids and
genetically assigned 1,464 embryos (from 70 experimental trials) to
their fathers. The presence of ovarian fluids significantly increased
the success of the more colorful competitors. Sperm of less inbred
competitors were more successful when tested in water only than in
diluted ovarian fluids. The kinship coefficients had no significant
effects on sperm traits or fertilization success in the presence of
ovarian fluids, although parallel stress tests on embryos had revealed
that females would profit more from mating with least related males
rather than most colored ones. We conclude that sperm of more colorful
males are best adapted to ovarian fluids, and that the observed reaction
norms suggest male strategies rather than cryptic female choice.