Russian Scientists Have Studied Marine Worm with Unique Spermatozoa
Russian scientists at A.V. Zhirmunsky National Scientific Centre of Marine Biology, HSE University, and Moscow State University have studied Phoronis embryolabi, a rare species of marine invertebrate found in the waters of the Sea of Japan. This species is notable for its unique reproductive system, which includes the development of larvae within the parent’s body and an unusual sperm structure. The study's findings contribute to our understanding of the evolutionary adaptations of marine organisms to extreme conditions. The study has been published in Zoologischer Anzeiger.
Phoronis embryolabi is a small marine worm that is viviparous, meaning it gives birth to live young, with larvae developing inside the parent’s body. This is an important adaptation for Phoronis embryolabi, which lives as a commensal organism—a type of symbiotic relationship where the commensal benefits while the host remains unaffected—in the holes of burrowing shrimp. It has been discovered that the reproductive process in this species involves the formation of spermatozoa with an unusual structure.
Spermatozoa are filamentous cells capable of moving within the confined spaces of the body. They develop in vasoperitoneal tissue (VPT) that surrounds blood vessels. 'This structure enables spermatozoa to move efficiently through narrow spaces filled with cells and embryos,' according to Elena Temereva, Professor of the Joint Department with RAS Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, HSE Faculty of Biology and Biotechnology.
Unlike other phoronid species, whose spermatozoa are V-shaped, Phoronis embryolabi’s spermatozoa maintain an elongated shape throughout all stages of maturity. The flagellum, essential for movement, is closely aligned with the cell body, which aids in movement through the narrow spaces of the body cavity. This is important, because the numerous embryos and other cells developing inside the body create additional challenges for sperm movement.
Sperm cells in Phoronis embryolabi, known as introsperm, possess unique adaptations typical of species with internal fertilisation. To reach the eggs, they must navigate through dense layers of cells and squeeze in the narrow spaces within the body. The researchers found that these spermatozoa are equipped with a collar around the base of the flagellum, which, along with undulating movements, enables them to move through the densely packed inner spaces of the animal. This movement resembles that of certain single-cell parasites, such as trypanosomes, which use similar mechanisms to move through a viscous medium.
For comparison, in other phoronid species, such as Phoronis pallida and Phoronopsis harmeri, introsperm are V-shaped cells composed of two parts: one part is the flagellum, while the other contains the nucleus and mitochondria. In Phoronis embryolabi, all components of the sperm are closely interconnected, which enhances their ability to move efficiently through narrow spaces. In addition, their spermatozoa are shorter than those of other species, which may also be an adaptation to the habitat conditions.
The study of spermatogenesis and sperm structure in Phoronis embryolabi provides valuable insights into how organisms adapt to extreme conditions. This information helps deepen our understanding of the evolution of reproductive biology in marine invertebrates and the factors that have influenced the development of complex reproductive strategies.
The unique adaptations of spermatozoa in Phoronis embryolabi are a crucial component of this species' survival strategy. The ability to move through narrow spaces and fertilise eggs in a body filled with embryos and other cells is an example of a successful evolutionary adaptation.
The research was carried out with support from the Russian Science Foundation.
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