The cabbage white butterfly might look sweet and innocent, but their sex life is a bizarre business of hard-cased jizz parcels, male dominance, and teeth-like chewing devices in the female’s reproductive tract. As if this odd reproductive system could not get any weirder, researchers believe it could be used to deepen our understanding of human infertility.
The study in the Proceedings of the National Academy of Sciences explores the reproduction of the cabbage white (Pieris rapae) butterflies, one of the world’s most common butterflies, native to Europe, North Africa, and Asia. It can also be seen in North America, Australia, and New Zealand after it was accidentally introduced during the 19th century.
The male’s ejaculate is made of “spermatophores”, a tough envelope containing sperm, proteins, carbohydrates, lipids, and other nutrients used to help females build eggs. The study worked out that females who mate just two or three times can build 40 percent of her eggs using these nutrients. Their sperm pouch is hard-shelled, so the female has to get into it using a toolbag of mechanical and biochemical methods. This is where it gets really weird.
"We discovered a surprising mechanical chewing device inside the female reproductive tract lined with a spectacular array of tooth-like structures [image below] that can gnaw through the hard outer shell in a matter of hours," biologist Nathan Morehouse from the University of Cincinnati said in a statement. "Without this mechanism we affectionately call the 'vagina dentata,' it would likely take a week or more to dissolve the hard protective shell with just her enzymes alone."
The scientists believe the males make it hard for the female to get to the sperm through this hard case as it helps maintain male dominance. The female can’t mate again until it is gone, which ensures more of his sperm fertilize her eggs.
The whole story is about complex interactions between male seminal fluids and female enzymes, oddly not too dissimilar to human conception. The idea goes, if scientists can understand the fine balance of these biochemical processes in butterflies, it could be used to understand human fertility too.
"Reproduction is a very interesting social interface where males and females have a conversation," explained Morehouse. "That conversation often begins with courtship, but doesn't stop after mating happens. It becomes a negotiation between the molecules of both sexes for the shared goal of producing offspring."
"There is magic all around us and the lovely thing about science is that sometimes clues that might actually help with health issues like human infertility can come from a butterfly in your own backyard."