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A team of paleontologists has discovered what they believe is the world’s oldest animal sperm, frozen in tree resin 100 million years ago inside a tiny crustacean in Myanmar.
The oldest known examples of fossilized animal sperm were previously only 17 million years old, according to the expert team led by Wang He of the Chinese Academy of Sciences in Nanjing.
The sperm were found inside an ostracod, a type of crustacean that has been around for 500 million years and can be found in many oceans today, they said in an article published Wednesday in the journal Proceedings of the Royal Society.
They were found in the body of a female specimen, indicating that it must have been fertilized shortly before it was trapped in amber, experts said.
Individual sperm were described as “giant”, measuring up to 4.6 times the size of the male’s body.
“This equates to about 7.30 meters (24 feet) in a 1.70 meter human being, so it takes a lot of energy to produce it,” Renate Matzke-Karasz from Ludwig Maximilian University Munich, co-author of the study, he told AFP.
The ostracod was also a new species that scientists have named “Myanmarcypris hui”.
Fossilized ostracod shells are common, but finding a specimen with “soft parts” is rare, experts said.
During the Cretaceous period, about 145 to 66 million years ago, the ostracods in question probably lived in the coastal waters of present-day Myanmar, where they were trapped in a stain of tree resin.
The specimen was given to researchers by a Chinese collector in 2017.
The tiny creatures are less than a millimeter long, but scientists made 3-D reconstructions of them to get a closer look, leading to what Wang described as “one of those special Eureka moments in the life of a investigator”.
In addition to sperm, the reconstructions also showed the distinctive muscular sperm pumps and penises (two of each) that male ostracods use to inseminate females.
“This specimen allowed us to confirm our hypothesis that these giant sperm cells existed 100 million years ago,” Matzke-Karasz said.
Until now, this theory had been based on the discovery in 2009 of large genitalia in crustaceans, suggesting the existence of correspondingly large sperm.
Most males in the animal world, including humans, produce tens of millions of tiny sperm, but ostracods are different; for them, quality is more important than quantity.
There are several contradictory theories about the evolutionary value of these giant sperm.
“For example, experiments have shown that in one group, a high degree of competition between males can lead to a longer sperm life, while in another group, a low degree of competition also led to a longer sperm life. sperm, “Matzke-Karasz said.
The researcher believes that giant sperm are a sign of good health on the part of males, a characteristic “favored” by females, whose genitalia evolved to accommodate an example of “coevolution.”
“Since many ostracods can reproduce parthenogenetically, without the need for males, sexual reproduction with giant sperm should have a distinct advantage over asexual reproduction,” Matzke-Karasz said.
“To show that the use of giant sperm in reproduction is not an evolutionary extravaganza doomed to extinction, but a serious long-term advantage to the survival of a species, we need to know when they first appeared.”
Scientists have been researching amber from Myanmar for decades, finding all manner of frozen treasures, including frogs, snakes, and a feathered dinosaur tail.
dac-fec / dlc / jxb
