Although barnacles are firmly attached to rocks, they use their long penises to locate and fertilize distant mates. However, researchers from the University of Alberta think that barnacles also release sperm into the ocean to fertilize distant mates; a behavior known as spermcast mating.
“Barnacles are a highly studied animal,” says Richard Palmer, a marine biologist at the University of Alberta, according to Nature. “It’s exciting to us to find something so totally new in a group that is so extensively studied.”
Barnacles typically live alone, which leaves them with with no potential mates close enough to have sex with. However, Palmer and his team found that barnacles are capable of spermcasting, an ability that gives them an entirely different way to procreate.
According to National Geographic, spermcast mating is exactly like what it sounds: A male barnacle ejaculates into the ocean, and female barnacles use the sperm to fertilize their eggs. Spermcasting is not a unique behavior in the animal world, as sponges, jellyfish and sea anenomes are also known to participate in this sexual behavior.
To determine whether barnacles self-fertilize or participate in spermcast mating, researchers gathered isolated individuals bearing egg masses, as well as isolated pairs where at least one parent carried egg masses. Using 16 single nucleotide polymorphism markers, they confirmed that a high percentage of eggs were fertilized with sperm taken from the water. In fact, sperm capture took place in 100 percent of isolated individuals and in 24 percent of individuals that had an adjacent partner. These results suggest that spermcast mating may be a common alternative to self-fertilization, according to researchers.
Barnacles are already famous for having extremely long penises for their size.
“Most free-living barnacles are hermaphroditic, and eggs are presumed to be fertilized either by pseudo-copulation or self-fertilization. Although the common northeast Pacific intertidal gooseneck barnacle, Pollicipes polymerus, is believed only to cross-fertilize, some isolated individuals well outside penis range nonetheless bear fertilized eggs. They must therefore either self-fertilize or—contrary to all prior expectations about barnacle mating—obtain sperm from the water,” write the researchers in the journal Proceedings of the Royal Society,
Barnacles have evolved the longest penises for their size – up to 8 times their body length – so they can locate and fertilize distant mates. In 2008, Palmer discovered that barnacles can change the size and shape of their penises to closely match local wave conditions. According to the researcher, when wave action is light, a longer penis can fertilize more mates, but when wave action is higher, a shorter penis can reach more mates.
Researchers note that several questions have yet to be answered, including: How widespread is spermcast mating compared with pseudo-copulation under normal conditions? How are sperm released and captured? Is behavior, limb form, sperm form or ejaculate form changed to increase the success of sperm capture?
Researchers are also puzzled as to how females get fertilized by sperm in water currents.
Additional research is needed to answer these questions, according to researchers.