Why are the sizes of sperm so different?

The sperm size of different animals varies greatly

Sperm is the most variable cell type known, ranging in size from 0.

"Researchers usually try to explain sperm diversity by focusing on how sperm compete to fertilize eggs or how females choose which sperm to fertilize their eggs," said Ariel Kahrl, a researcher in the Department of Zoology at Stockholm University

"But it turns out that there is still one piece missing in this mystery-where the sperm and egg meet will also affect the size of the sperm

To study how the location of fertilization affects sperm evolution, the researchers collected sperm size data from more than 3,200 animals — from corals to mammals, including humans — and classified each species according to where the sperm and egg meet

"In vivo fertilization of species - just like mammals, birds and insects, sperm fertilizes eggs in the female body, and in species and in vitro fertilization - such as sea urchins and many fish - sperm and eggs are released into the water and outside of fertilization.

Researchers found that compared with animals that use external fertilization, the average life span of sperm from internally fertilized animals is 6 times longer and the size changes faster

Rhonda Snook, one of the authors of this paper and a professor of zoology, said: "When sperm are released from the outside, the choice will keep the sperm volume small so that the male can produce a lot of sperm

The researchers also examined the third form of fertilization found in invertebrates, that is, sperm casting.

John Fitzpatrick, associate professor of zoology at Stockholm University and the senior author of the study, said: “Precision casting represents a mixture of internal and external fertilization, which gives us the opportunity to see which part of the fertilization process affects the sperm’s development.

In the sperm manager, studies have found that sperm is as small as an external fertilizer, but evolves quickly like an internal fertilizer

"Our results clearly show that the interaction between sperm and female helps to produce the huge diversity of sperm sizes we see in animals today

Since humans are fertilizers in the body, does this mean that men have super-large sperm? But this is not the case; the size of human sperm is similar to the size of sperm released by animals in water

"In larger animals, such as humans, sperm is diluted in the female reproductive tract

More information about this research

The idea that the fertilization environment affects sperm size has existed for more than 60 years

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 "Fertilization mode drives sperm length evolution across the animal tree of life" in Nature Ecology and Evolution : Link DOI number https:/ / doi.