Data from: Possible glimpses into early speciation: the effect of ovarian fluid on sperm velocity accords with post-copulatory isolation between two guppy populations

Identifying mechanisms of reproductive isolation is key to understanding
speciation. Among the putative mechanisms underlying reproductive
isolation, sperm-female interactions (postmating-prezygotic barriers) are
arguably the hardest to identify, not least because these are likely to
operate at the cellular or molecular level. Yet sperm-female interactions
offer great potential to prevent the transfer of genetic information
between different populations at the initial stages of speciation. Here we
provide a preliminary test for the presence of a putative
postmating-prezygotic barrier operating between three populations of
Trinidadian guppies (Poecilia reticulata), an internally fertilizing fish
that inhabits streams with different levels of connectivity across
Trinidad. We experimentally evaluate the effect of female ovarian fluid on
sperm velocity (a predictor of competitive fertilization success)
according to whether males and females were from the same (native) or
different (foreign) populations. Our results reveal the potential for
ovarian fluid to act as a postmating-prezygotic barrier between two
populations from different drainages, but also that the strength of this
barrier is different among populations. This result may explain the
previous finding that, in some populations, sperm from native males have
precedence over foreign sperm, which could eventually lead to reproductive
isolation between these populations.