Data from: Evolution and co-evolution of the suck behaviour, a postcopulatory female resistance trait that manipulates received ejaculate

Sexual conflicts over the post-mating fate of received ejaculate can
favour traits in one sex that are costly to the other. Reciprocally mating
hermaphrodites face unique challenges as they mate simultaneously in both
the male and female role, potentially leading to receipt of unwanted
ejaculate. Reciprocal mating can then give rise to postcopulatory female
resistance traits that allow manipulation of received ejaculate. A
putative example is the suck behaviour, observed in the flatworm genus
Macrostomum. It involves the sperm recipient placing its pharynx over its
own female genital opening and appearing to suck, likely removing received
ejaculate after mating. The genus also contains
hypodermically-inseminating species that presumably exhibit unilateral
mating and have not been observed to suck. Here, we examine the evolution
of the suck behaviour in the Macrostomum genus, aiming to document the
mating behaviour in 64 species. First, we provide videographic evidence
that ejaculate is indeed removed during the suck behaviour in a
reciprocally mating species, Macrostomum hamatum. Next, we show positive
evolutionary correlations between the presence, duration and frequency of
reciprocal mating behaviour and the suck behaviour, providing clear
evidence that the suck behaviour co-evolves with reciprocal mating
behaviour. Finally, we show an association between reproductive behaviour
and reproductive morphology, suggesting that reproductive morphology can
be used to infer a species' mating behaviour. Together, our study
demonstrates sexually antagonistic coevolution leading to the evolution of
a postcopulatory behavioural trait that functions as a female
counter-adaptation allowing individuals to gain control over received
ejaculate in a hermaphroditic sexual system.