How can nematodes mate without spicules?

Males of roundworms (Nematoda) usually possess cuticular copulatory organs (spicules) that are inserted in the female’s vulva to attach the male to the female and to widen the vulva against the inner body pressure for sperm transfer. Among free-living nematodes, the only exception of this rule is Myolaimus where the males lack spicules. Until now there exist no reports on how mating is achieved in Myolaimus. Here we show that sperm transfer in Myolaimus apparently involves at least six different secretions of the male gonoduct that are pumped into a sack-like cuticular protrusion of the female’s vulva to form a spermatophore-like capsule. The role of gonoduct glands in male nematodes (even in the model organism Caenorhabditis elegans) is poorly understood. Here we present the first study explaining the role of different vas deferens gland products in nematodes and argue that Myolaimus males lost their spicules as a result of sperm competition.