Among all animals, Drosophila bifurca or the fruit fly reigns supreme as having the longest sperm. Researchers found that a fruit fly's sperm is 20 times longer than its own body and 1,000 times longer than that of a male human. Talk about David beating Goliath.
Perhaps an ironic extreme, the scientific community has long accepted that the tiniest animals bear the biggest sperms and vice versa. A recent study added a fascinating new extreme to the sperm Olympics. Researchers found that both sperm length and numbers are defined by the size of the animal. A mouse's single sperm measures 124 micrometers long while an elephant's swimmer is just 56 micrometers long. A mouse ejaculates approximately 9.5 million sperms while an elephant releases over 200 billion sperms.
In animal species whose females copulate with multiple partners, the sperms are thrown into a tight competition to fertilize an egg. Researchers found that larger sperms among small animals have the upper hand. But in larger animals, the small sperm released in high volumes seems advantageous.
Animal sperms vary not just in length and volume but also in shapes. As for the "big-time" fruit flies, one tightly coiled sperm measures as astounding 5.8 centimeters (2.3 inches) long, a little longer than your average passport photo. Researchers theorized that the evolutionary trade-off between volume and length size has something to do with the size of the females' reproductive system.
"Since elephants are bigger than mice, it seems that their sperm have a higher risk of being diluted or lost in the bigger female reproductive tract. In other words, sperm number becomes far more important than sperm size," said University of Zurich's Stefan Lüpold who co-wrote the study. Lüpold added that dilution of sperm is not that big an issue in smaller animals.
A male fruit fly's testes make up nearly 11 percent of its entire body weight, enabling it to produce massive sperms in terms of length. What's fascinating is that the fruit fly's ability to grow enormous sexual organ take up most of its energy. In turn, it delays the fruit fly's sexual maturity.
The researchers published their study in the Proceedings of the Royal Society B journal.
