Investigating the effects of reduced maternal investment in sea stars

Hello! I am currently researching the effects of reduced maternal investment in large egged sea stars. Right now, I am working with the sea star Henricia. Initially, I had planned to use the grant to purchase a different genus of large-egged sea star, Solaster, but the long winter has not provided optimal conditions for our supplier to collect the sea stars from Maine. However, in his last shipment to Allen lab, the supplier provided a several extra Henricia, which allowed us to begin preliminary work on another large-egged sea star while waiting for the Solaster. Additionally, on Dr. Allen’s last trip to Maine, he collected a few individuals of Henricia, and as a result we had plenty to work with!

Henricia produce extremely large, yolky eggs and they also brood their young all the way through metamorphosis. Most marine invertebrates broadcast spawn their gametes into the water column, leaving their potential offspring to fend for themselves, which contrasts with the brooding behavior of Henricia. Additionally, Henricia eggs are approximately ten times larger than the average size of sea star eggs. Henricia invests a great deal of more energy per offspring than most marine invertebrates. My initial plan was to fertilize the eggs and wait for them to develop into two-cell blastomeres, then ablate one cell. This would artificially halve the available nutrition for the developing embryo, since the extremely yolky egg serves as the sole source of nutrition for these non-feeding embryos.

My advisor Dr. Allen had not worked with this genus before, and so we were not sure of its developmental timeline. He had spawned the sea stars a few weeks ago and found that the spawning time was much longer than in other sea stars he had worked with. The males spawned approximately an hour after injection of 1-methyl adenine, but the females took significantly longer, delaying spawning until three to four hours post-injection. After the females had spawned, we mixed the sperm and eggs and checked the now-fertilized eggs every few hours for signs of cleavage. They took a very long time to cleave into two cells, cleaving between twenty-one and thirty-four hours. Since the embryos’ development took much longer than we had anticipated, we decided to just observe this clutch and see how long it would take them to metamorphose into juveniles. We placed some of the eggs into tea infusers and put those into aquariums. Others we placed into Pyrex bowls filled with water from the same aquarium. We used two methods of containment to see if the glass bowls, which are a more practical option, still produce viable juveniles.

Over the next few weeks, the juveniles in the bowls began to die, while the ones in the tea infusers stayed healthy. Unfortunately some of the tea infusers had holes in the mesh from when they housed hungry urchins, and some of the embryos escaped into the tank, never to be seen again. Once we began water changes for the embryos in the bowls and limited handling of the embryos overall, the death rate began to slow. Since the embryos are so large and yolky, exposure to the surface tension of the water can be enough to lyse the embryos.

Even with love and attention, these most of these embryos did not make it and we decided to spawn them again, to better quantify their development timeline. I hope to confirm that Henricia is a viable study system in the lab for investigating maternal investment!

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