Discovery in 100-million-year-old amber reveals sexual intercourse of ostracods

The small bivalved crustacean ostracodes are the most abundant fossilized arthropods after the Ordovician and play an important role in paleoenvironmental reconstruction and evolutionary biology.

Most of the fossilized ostracods are represented by calcified shells, and their soft parts, which can provide invaluable information about the ancient ostracode auto talk ology l g, are extremely rare.

Recently, Dr. Wang He and Prof. Wang Bo of the Nanjing Institute of Geology and Paleontology at the Nanjing Institute of the Chinese Academy of Sciences (NIGPAS), and their collaborators performed exceptionally well-preserved ostracodes with soft to moderate parts (appendages and reproductive organs). -Critius Myanmar Amber (million 100 million years old), who revealed the sexual intercourse of Ostracodes.

The study was published in Proceedings of the Royal Society b 15 Sept.

The Ostracode Assembly in Amber is made up of 39 individuals in an amber piece and includes men, women and teenagers.

X-ray micro-computed tomography was used to obtain high-resolution three-dimensional images of their soft parts. MicrocT reconstruction has provided direct evidence of female semi-eclipse on male spleen, sperm pumps (zenker organs), hemipans, eggs and female sperm.

This is the first time that a large Ostracode sperm has been found in a Cretaceous Ostracode fossil; Its length was at least one-third of the length of Ostrakode’s body. This discovery is also an ancient animal sperm record, and is about 500 million years older than the previous ancient fossil record of animal sperm.

Analysis of fossilized and surviving ostracodes shows that during sexual reproduction, the male uses his sexual demorphic fifth organ, which contains hook-like endopods, while introducing his hemipens into his sexual vagina. The male pair transfers exceptionally long but stable sperm to the female through the male hemisphere after the zenker organs.

The Zenker organ is easily identified in the existing cypridoid strocodes as a large, prickly, sclerotized portion of the various spermatic tubes. The muscle fibers along the limb connect numerous spines, often arranged in a vortex that is characteristic of classification at the familial level.

Once in the female, the semen is pushed over two long sperm canals, each ending in a final ejaculation like a bag for sperm collection; There, they eventually become dynamic, aligning themselves in a more organized assembly and fertilizing the egg during the process of oviposition.

Research has shown that the repository of reproductive behavior in ostracodes, which is associated with significant morphological adaptation, has remained the same for at least 100 million years – the highest example of the stability of evolution.

The appearance of a complex reproductive mechanism and the late Mesozoic explosive radiation at the end of the superfamily Cypridoidia may have been important contributors to the success of improved mating in large sperm, including most nonmarine ostracode species today.