How tubeworms reproduce and develop in high pressure vessels

by Philipp Pröts

One topic of this cruise is to investigate the reproduction and embryonal development of Riftia pachyptila. The giant tubeworm lives in warm areas of hydrothermal vents where they build their housing tubes on the deep ocean floor. These animals have separate sexes. Males and females are known to produce more or less continuously many sperm and eggs. In nature, males release bundles of sperm into the seawater through an opening. These sperm travel in the water to find a female and enter through the female opening, crawl inside to the eggs and fertilize them. The female then releases the fertilized eggs into the seawater where further development into a larva happens.

(Top left) Riftia life cycle, (center left) sex differences in Riftia, attribution: Monika Bright (CC-BY-NC-SA 4.0); (center right) male Riftia, (top right) female Riftia, attribution: Philipp Pröts (CC-BY-NC-SA 4.0).

While the grown-up animals live together with their symbiont, a sulfur bacteria called Candidatus Endoriftia persephone, the developmental stages live alone while traveling in the seawater to develop into a larva. The goal is to study the gene expressions in these developmental stages, to get an idea what they do, and then compare them to adult gene expressions when they live together with their symbiont. We will mimic this process in the lab. First, we bring some animals onboard the ship. The animals are highly stressed without about 250 bar pressure they experience at the deep-sea vents. It has been observed often that some males release their sperm and some females release their eggs. These we will collect and mix for fertilization. This way we expect that they develop normally, which will grant us access to different embryonal stages. We will measure their oxygen consumption over time, take nice pictures of the individual cell stages with a light microscope and preserve several #embryos for further molecular and morphological investigations back at the university.

(Left) Riftia gametes brought together. Attribution: André Luiz de Oliveira (CC-BY-NC-SA 4.0). (Right) André Luiz de Oliveira and Philipp Pröts working with the pressure vessel on board Falkor(too) of the Schmidt Ocean Institute. Attribution: Salvador Espada (CC-BY-NC-SA 4.0)