414: Love Darts in the Backyard
Koene and Schulenberg found that love darts are indeed part of a grand sexual arms race. Love darts have evolved many times, initially as simple cones but then turning into elaborate harpoons in some lineages. In the same species in which these ornate weapons have evolved, snails have also evolved more powerful tactics for delivering their sperm, including increasingly complex glands where the darts and hormones are produced. These aggressive tactics have evolved, it seems, in response to the evolution of female choice. Species with elaborate love darts also have spermatophore-receving organs that have long, maze-like tunnels through which the sperm have to travel. By forcing sperm to travel further, the snails can cut down the increased survival of the sperm thanks to the dart-delivered hormones.
Evolutionary hypotheses tested, common descent, and neat biology. Nice pictures, too.