Some of the largest sperm come from the smallest animals. Take the tiny fruit flies that hover over overripe bananas. The male flies hold the world record for longest sperm, at a whopping two inches.
That’s roughly twenty times their body size (and about 1,000 times the length of human sperm, which are 0. 05 millimeters). The physics of this presents a real packing nightmare. It’s like jamming thousands of strands of fishing line into a shoe box.
The risk is that the male sex cells will get completely tangled up and unable to get to an egg. Yet, somehow, this doesn’t happen, and scientists have long wondered why. A new study in Nature Physics offers an answer.
Researchers at the Flatiron Institute in New York took a look at a readily available cousin: Drosophila melanogaster, the laboratory fruit fly that scientists use to study a wide range of biological processes, from genetics to cancer.
Its sperm are about two millimeters long, nearly as long as the fly itself. When Michael Shelley, an applied mathematician, and his team viewed the sperm under a microscope, they found that they were not clumped into a messy ball.
Instead, they were neatly stacked in parallel rows, like spaghetti strands that stay together as they swirl in a pot of water. The sperm were lined up side by side, bending inside the confines of the sperm storage organ.
The whole mass seemed to move together in a smooth, slow wave, while the sperm themselves were moving.
To understand how a sperm’s individual movements corresponded to the whole, the scientists conducted several more experiments using high-resolution visualizing techniques, including dyeing the sperm different glowing colors and tracking them in real time.
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