Penis fencing

Mating Pseudobiceros bedfordi

Penis fencing

Penis fencing is a mating behavior observed in certain species of marine flatworms, particularly in the genus Pseudobiceros. This unique reproductive strategy involves the reciprocal insemination between two individuals, where each flatworm attempts to inseminate the other with its penis.

Behavior

During the mating ritual, two flatworms engage in a form of combat known as penis fencing. Each flatworm possesses a sharp, needle-like penis that it uses to inject sperm into its partner. The goal of each individual is to inseminate the other while avoiding being inseminated itself. This behavior is believed to be a result of sexual selection, where the flatworms compete to pass on their genes to the next generation.

Mechanism

The penis of a flatworm is equipped with spines or hooks that help anchor it to the partner's body during insemination. The flatworms engage in a complex dance, attempting to pierce the skin of the other with their penis while avoiding being penetrated themselves. The successful inseminator gains a reproductive advantage by transferring its sperm to the partner.

Evolutionary Significance

Penis fencing is thought to have evolved as a way for flatworms to increase their reproductive success in environments where mates may be scarce. By engaging in this behavior, flatworms can ensure that they have a chance to pass on their genes even in situations where finding a mate is challenging.