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Preserved in amber from Myanmar, an international team of paleontologists discovered giant sperm from a tiny 100-million-year-old crustacean, Ludwig Maximilians University (LMU) reported in Munich on Wednesday. The finding thus provides clear indications of how the animals reproduced.
According to the university, the oldest evidence of sperm belongs to a previously unknown species of crustacean, which the researchers named Myanmarcypris hui. A female mussel crab was found, apparently mating shortly before being trapped by tree sap. The sperm detected are huge, that is, many times longer than the animals themselves.
The newly discovered species is one of the so-called ostracods, the LMU explained. Fossil shells of ostracods, which have existed for 500 million years, are frequently found. In the Myanmar specimen, the researchers even discovered fossilized “soft tissues”, including internal organs and reproductive organs. “It was an extremely rare opportunity to learn something about the evolution of these organs,” explained Munich geobiologist Renate Matzke-Karasz, who participated in the analysis.
With the help of X-ray microscopy, a 3D reconstruction of the ostracode was created. The reproductive organs and the hundred million year old sperm were also visible. The reconstructions would also have shown the characteristic muscular sperm pumps and two penises with which male mussel crabs mate with females. Never before has such an ancient and sophisticated evolutionary mechanism been documented in such detail.
According to the scientists, the finding raises the question of whether reproduction with giant sperm can be an evolutionarily stable path. Males of most animals, including humans, usually produce tiny sperm in large numbers. Only a few animals, including some fruit flies in addition to ostracods, produced a relatively small number of sperm that are many times longer than the animals themselves.
“To show that the use of giant sperm in reproduction is not an evolutionary quirk, but can be a permanent benefit to the survival of a species, we need to know when they first appeared,” Matzke-Karas explained. Evidence of giant sperm that have been successful for more than a hundred million years shows the success of this strategy. “Sexual reproduction with giant spermatozoa must therefore be advantageous in evolutionary terms”, explained the scientist.
The so-called Kachin amber from Myanmar has brought back excellent finds in recent years, including frogs, snakes, and a feathered dinosaur tail. Hundreds of new species have been described in the last five years. This has led many evolutionary biologists to rethink common hypotheses about how certain lineages and ecological relationships developed.
