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Female reproductive fluids (FRF) serve key reproductive functions in
sexually reproducing animals, including modifying the way sperm swim and
detect eggs, and influencing sperm lifespan. Despite the central role of
FRF during fertilisation, we know surprisingly little about sperm-FRF
interactions under different environmental conditions. Theory suggests
that, in external fertilisers, FRF may ‘rescue’ sperm from ageing effects
as they search to fertilise eggs. Here, we test the interaction between
these two fundamental properties of the fertilisation environment,
ejaculate age (i.e., time since ejaculation) and FRF, on a range of
functional sperm phenotypes in a broadcast spawning mussel, Mytilus
galloprovincialis. We found that the effects of ejaculate age on
multivariate sperm motility traits and total sperm motility were altered
by FRF, and that longer-lived sperm exhibit stronger, likely more
advantageous, responses to FRF after periods of ageing. We also detected
significant among-male variation in the relationship between sperm
motility traits and ejaculate age; notably, these patterns were only
revealed when sperm encountered FRF. Collectively these findings
underscore the importance of considering female reproductive physiology
when interpreting ageing-related declines in sperm motility, as doing so
may expose important sources of variation in sperm phenotypic plasticity
among males and environments.
109 views reported since publication in 2023.