Frozen in time

A very proud Cas with his cryo rig.

Friends, I want to tell you about two strategies we tried out this spawning season to freeze our little babies in time. Yes, I mean that literally. 

One of our major questions was whether corals from different genetic lineages can cross-fertilize one another. If they can't, then our lineages might be different species. We're keeping track of the exact time when each individual spawns, because that way we can see if there's any temporal reproductive isolation. If you spawn at different times, your gametes may never meet. But we also want to figure out whether the mixing of eggs and sperm from different lineages can produce viable embryos. It's impossible to monitor every coral on every reef, so we brought about 100 of them into the lab. That's a very small sample of the population. What if individuals from our different lineages just happen to spawn at slightly different times, and we don't have their gametes at the same time? We'd never be able to check if they can fertilize.

Enter cryopreservation. Honestly, when Cas and Sarah (my co-PI) first suggested we try cryopreserving some of our gametes, I thought it was crazy talk. I had visions in my head of a human body farm in a sci-fi horror movie. But it's not actually that complicated. You need a thermally-insulated container, a temperature probe, some 3D-printed parts, and liquid nitrogen. Using the design from a recently-published paper, Cas gathered all the parts we needed and arranged for us to cryopreserve sperm in Palau. 

It worked fantastically. Without giving too much away, I can tell you we were able to cryopreserve sperm, and we were able to thaw the sperm and use it for cross-fertilization assays later. The results will show us whether our lineages are reproductively compatible. It's super exciting stuff!

Nothing to see here, just a microscope 
in a cupboard.

The second way that we froze embryos in time was through time-lapse photography. Matthew wanted to figure out how quickly the cellular divisions take place in Porites lobata embryos. The only viable way to do that is honestly to watch them divide. It's like watching paint dry. Plus, we were super busy on spawning nights putting together all of our crosses, so we didn't have time to monitor dividing embryos like a hawk. As a way around all that, Matthew set up a microscope and wrote a quick program that would click the mouse on his laptop to take a picture every few minutes. He needed a sheltered area with no wind, where the microscope was unlikely to be disturbed and the air was at ambient temperature. After considering the options, it seemed the best place to set up the microscope was the cupboard in his room. He turned off the air conditioning, made some space among his clothes, and set up the microscope and a lighting rig. A cord led out the cracked door to his laptop on the bed. As soon as we had some fertilized embryos, Matthew took a sub-sample in a petri dish up to his room and started the program. 

And you know what, it worked. He got the information we needed. The photos show the first few cellular divisions of our embryos, and we can tell how long each division took based on the time-stamps on the photos. It was super exciting to get those data. 

We're making a lot of progress and collecting great data in Palau!