The discovery of giant 100 million year old sperm cells – the oldest known sperm cells

In another fascinating photograph from the darker times, an international team of paleontologists reported the discovery of specimens of a minuscule crustacean, dating back to Cretaceous (About 100 million years ago), preserved in amber samples from Myanmar. The most spectacular discovery is a single woman, who sets out on close examination to include giant sperm cells in her reproductive tract.

In fact, it is the oldest fossil in which sperm cells have been conclusively identified. In addition, the specimen represents a previously unknown species of crustacean, named Myanmarcapris huii. M. Hui was an ostracode, as indicated by the clearly coupled calcareous valves that formed the carapace, the form of which recalls as a muscular shell.

Ostracodes have been around for 500 million years, and thousands of modern species have been described. They are found in oceans and in freshwater lakes and rivers. The fossil shells of these crustaceans are by no means rare, but specimens preserved in Burmese amber reveal details of their internal organs, including those involved in reproduction.

“We have a very rare opportunity to learn more about the development of these organs,” says Ludwig-Maximilians-Université (LMU) in Munich geologist Ranet Mattek-Karz, who played a major role in the morphological analysis of fossils Played.

During the Cretaceous period, ostracods lived in the coastal and inland waters of Myanmar, which were dominated by forests that produced trees in large quantities of resin. The newly described specimens are one of several organisms that were trapped in oozing blobs of gooey matter.

In recent years, amber found in Kachin province has received a spectacular troop of fossils, including frogs and snakes, as well as part of a potent dinosaur (according to new evidence, this specimen is actually May represent an unusual lizard). Over the past 5 years, hundreds of previously unknown species have been described based on these findings. In fact, many of them have forced evolutionary biologists to rethink traditional astrology, which deals with phytolanetic and ecological relationships.

New ostracod samples were analyzed with the help of computer-assisted 3D X-ray reconstructions. The pictures contained astonishing description of the anatomy of these animals, from their small organs to their reproductive organs. And in a female sample, Matzke-Karz and her colleagues discovered ripe sperm. The cells were discovered in paired sperm receptors in which they were stored after copulation, ready for release when the female’s eggs were cured.

“This woman should have intercourse shortly before engaging in resin,” he told Wang of the Chinese Academy of Sciences in Nanjing. X-ray images also revealed a pair of sperm pumps and pennies that the male ostracods put into the twin gonopores of females.

The discovery of Burmese amber provides unprecedented insight into an unexpectedly ancient and advanced example of evolutionary expertise. Matzke-Karz states, “The complexity of the reproductive system in these samples raises the question of whether investment in giant sperm cells may represent an evolutionarily stable strategy. Males of most animal species (including humans) produce very small numbers of very small sperm. Comparatively some animals, including some fruits – and of course, Ostracode – have opted for a different approach. They make a relatively small number of oversized sperm, whose inspiratory tails are several times longer than in animals.

“To prove that the use of giant sperm is not an extraordinary fad on the part of evolution, but a viable strategy that can provide a lasting advantage that enables the species to live longer, we need to take this mode Must establish breeding appeared first, ”says Matzke-Karz.

Examples of fossilized sperm cells are extremely rare. The oldest known ostracode sperm (before the new discovery) are 17 million years old, and the previous record age, 50 Myr, was assumed by one species of worm. New evidence raises that age by a factor of at least two.

The fact that animals had developed giant sperm 100 million years ago means that this reproductive strategy may actually be successful in the (very) long term, Matzke-Karz explains. “This is a very impressive record for a feature that requires considerable investment from both males and females of the species. From an evolutionary point of view, sexual reproduction with the help of giant sperm should therefore be a completely profitable strategy. ”

References: “Wang, Rente Matke-Karz, David J. Hornay, Jiangdong Zhao, Mizhen Cao, Haichun Zhang and Bo Wang, giant sperm in reproductive organs and giant sperm ostestodes by 16 September 2020”. Proceedings of the Royal Society B.
DOI: 10.1098 / r dioxide.2020.1661