Sperm size varies greatly depending on the animal species. But why do sperm sizes fluctuate so much when they share the same job?In a new article published in Nature Ecology and EvolutionResearchers at Stockholm University have shown that animal sperm evolution is overcharged only when sperm swim in females.
Sperm are the most variable cell types known and vary in size from 0.002 millimeters in freshwater rotifers to nearly 6 centimeters in fruit flies.Explanation of reason sperm Very variable Main focus In evolutionary biology over the last 100 years, sperm always have the same function, no matter what they come from. In other words, fertilization. egg..
“Researchers usually try to explain sperm diversity by focusing on how sperm compete to fertilize an egg, or how women choose which sperm fertilize an egg. “Masu,” says Ariel Karl, a researcher at Stockholm University’s Faculty of Zoology.
“But it turns out that there are pieces of the puzzle. Where sperm and eggs meet can also affect sperm size.”
To investigate how the location of fertilization affects sperm evolution, researchers have compiled data on more than 3,200 sperm sizes. Animal speciesFrom corals to mammals, including humans, we have categorized various types based on where sperms and eggs meet.
“In some species of in vitro fertilization, such as mammals, birds and insects, sperm fertilize eggs in the female body, whereas in some species of in vitro fertilization, such as sea urchins and many fish species, sperm and eggs are underwater. Fertilization occurs externally. The female body, ”explains Ariel Karl.
Researchers have found that sperm are on average 6 times longer and change in size more rapidly. animal Those that use internal fertilization compared to the sperm of animals that use in vitro fertilization.
“When sperm are released to the outside, choice keeps the sperm size small so that men can produce large amounts of sperm,” says Ronda Snook, a professor of zoology and author of the paper. “But when sperm are transferred to females with internal fertilizer, males may compete better with larger sperms, and females may prefer to fertilize eggs with larger sperms.”
Researchers also investigated a third form of fertilization found in invertebrates called sperm casting. In this case, the sperm are released to the outside, filtered from the water by the female, and fertilize the egg inside the female.
“Sperm casting represents a mixture of internal and external fertilization, giving us the opportunity to see which parts of the fertilization process influenced sperm evolution,” said Stockholm University’s Zoology. Associate Professor and lead author of the study, John Fitzpatrick, said.
In sperm casters, studies have shown that sperm are as small as external fertilizers but evolve rapidly like internal fertilizers.
“Our results clearly show that the interaction between sperm and female helps to produce the tremendous diversity of sperm size found in animals today. Between sperm and female. The more likely it is to interact, the faster sperm will evolve, “says John Fitzpatrick.
Since humans are internal fertilizers, does this mean that men have super-large sperm? I found that it wasn’t. Human sperm are about the same size as animals that release sperm into the water.
“For animals Big body, Like humans, sperm are diluted in the female reproductive tract. From a sperm point of view, it doesn’t matter if the dilution is done inside the woman or at sea. Dilution keeps sperm small. Sperm become super-large only when they are trapped in a woman’s small space, “explains Ariel Karl.
The idea that the fertilization environment affects sperm size for more than 60 years. However, researchers have not been able to test this idea through the evolution of animals. In this article, researchers at Stockholm University have compiled the largest database of sperm morphology ever collected and show that when sperm function in a woman’s body, sperm size increases and changes rapidly. I am.
Fertilization mode promotes the evolution of sperm length throughout the tree of life of the animal. Nature Ecology and Evolution (2021). DOI: 10.1038 / s41559-021-01488-y , www.nature.com/articles/s41559-021-01488-y
Quote: Https: //phys.org/news/2021-06-females-supercharge-sperm-evolution-animals.html Obtained on June 21, 2021 from Animal Female Supercharged Sperm Evolution (June 2021) 21st)
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