A 100-million-year-old Myanmar amber has housed the world's oldest-ever sample of animal sperm. To add more, the sperms are enormously long as it is several times larger than human sperm. This sperm came from a shrimp-like crustacean that is smaller than a poppyseed.
The study was published in Proceedings of the Royal Society B: Biological Sciences.
Large 100-million-year-old Sperm
The sperm cell approximately measures 0.6 millimeters and belonged to a still-living organism under the class of microcrustacean called ostracods. these organisms are known to house sperms that are up to ten times larger than they are. It seems impossible but when these organisms are twisted and tangled to form a ball, they could travel through the female reproductive more easily.
The researchers used a micro-CT scan to reveal 39 of their ancient crustacean relatives that are all preserved in the same slice of amber. What's more astonishing is that this frozen community has the same reproductive traits that are still seen in ostracods today.
Moreover, these fossilized bodies also contained eggs, sperm pumps, and female receptacles filled with sperm. The authors said that the expanded seminal structures of the female due to being filled with sperm indicate that there was successful copulation that happened before these animals were entrapped in the amber.
Although the authors admit that it is hard to measure individual cells in these tangled masses, they estimate that the sperms measures at least 200 µm long (0.2 mm), which is one-third of the entire body length of the ancient creature.
Ostracod fossils from millions of years ago have already shown hints of giant reproductive organs but this new discovery is by far the largest sperms ever found.
In 2014, sperms of 16-million-year-old ostracods were discovered in Australia that measures 1.2 mm long. But this new specimen from Myanmar is 83 million years older, doubling the oldest unequivocal fossil animal sperm.
Read Also: Scientists Disprove 340-Year-Old Belief on How Sperm Moves: Apparently, They Like to Spin
Sexual Reproduction of Ostracods
Both ancient and modern ostracods most likely use their fifth limb as a hook to grab unto their partners during sexual reproduction. Once they grab hold of the female ostracod, they insert their erectile tissue and pump out immobile sperm and pushes it up two long sperm canals.
The authors think that the sperms begin to move once inside the seminal receptacles and settle into an "organized assemblage" to begin fertilization.
Although it might sound contradictory that some smaller creatures produce the largest sperm, when females copulate to more than one mate, the sperm must compete. Scientists think that larger sperms could be advantageous in fertilizing the egg. But a giant sperm also comes with a high price for both females and males.
An animal has to allocate a large portion of its body to house such large sperm, and some species dedicate one-third of their body volume to reproduction alone.
It is still a mystery today how these animals were able to evolve and carry such traits until today because direct evidence is not available. This new discovery is remarkable in the sense that it shows the similarities of ancient ostracods to their modern counterparts.
According to the authors, the male clasper, sperm pumps, female seminal receptacles, and hemipenes, which are all associated with morphological adaptations, have remained unchanged over millions of years.
Read More: Scientists Create 'Surrogate Sires' to Improve Food Production
Check out more news and information on Cells on Science Times.
