Hellllloooooo, love-dart. When molluscs mate, the male shoots this little spear into the female depicted here protruding from the female's head:
But why all the she-snail hating. Chase and Blanchard show in this work that the purpose of the dart is for the male snail to convey his man mucus into the female. That is his man mucus, not his royal jelly. The man mucus apparently contains some type of hormone or enzyme that makes the male more likely to successfully sire offspring.
I can't even assimilate this information from this paper. It is so gross yet so cool. Even the abstract makes me shiver.
Many of the seemingly bizarre animal behaviours can be understood only by acknowledging the power of sex to shape evolution. A case in point is the so-called love-dart that some terrestrial molluscs shoot at their prospective sexual partners. Given that the likelihood of copulation is not different after solid hits than after complete misses, why do these suitors act so violently towards their chosen mates? Previously, it was shown that successful dart shooting enhances paternity. We conducted an experiment to determine whether the dart achieves its effect by a purely mechanical action or by transferring a bioactive substance. We found that injections of mucus from a gland associated with the dart more than doubled paternity relative to injections of saline. These results support the hypothesis that the dart transfers a substance capable of reconfiguring the spermatophore-receiving organs. While dart shooting probably evolved as the result of sperm competition, a role for cryptic female choice cannot be excluded. Our results imply that if cryptic female choice is operating in this system, it is likely to be based on the properties of the mucus and not on properties of the dart itself. Since we also found evidence of early-male sperm precedence, we conclude that snails can optimize their reproductive success by mating with virgins and shooting their darts accurately.
Can female choice be involved in selecting the quality of the mucus? Well let me just tell you that I know some females who are pretty picky about their mucus.
Can males optimize their reproductive success by mating with virgins and shooting accurately? The authors have this to say:
We conclude that snails have two ways in which to optimize their reproductive success: by shooting darts accurately and by mating with virgins. It is unknown, however, whether snails are able to either control the accuracy of their dart shots or identify virgin partners.
Ain't that the truth, brother...ain't that the truth.
Hat-tip: Faculty of 1000.
I need to bookmark this for one of the future Friday Weird Sex Blogging editions....