Over the weekend, our infected sea stars survived, as did all our Alaskan stars. So far so good! Today we made the decision to proceed with the challenge trials – this is where we take viruses out of the Seattle Aquarium stars and then inject them into the Alaskan animals to see how they respond. Finally, some actual experiments!
The first step was to adjust the experimental tanks to the same salinity and nutrient concentrations, before transferring our Alaskan Evasterias. Vital data on animal size and weight were taken, along with samples to determine their ambient micro biome, coelomocyte concentration, and samples for molecular work (transcriptomics, SSaDV prevalence, bacterial abundance, virioplankton abundance, etc). We’ve learned from experience that the coelomocytes (kind of like blood cells) behave somewhat differently from surface tissues, so we collected some tube feet as well. We’ve also noted in previous work that the virus appears in the water column (i.e. is shed) well before any symptoms develop, so monitoring free viral abundance in the aquarium water will also help us to understand its dynamics in nature.
Elliot and Ian prepared a viral size fraction from one of the Seattle Aquarium sea stars, which had been wild caught a few weeks prior in the Puget Sound, and which had a fairly high SSaDV load. The animal itself wasn’t displaying any disease signs yet, but had done so a few weeks prior. Elliot had the rather grusome task to removing tube feet and epidermis from the animal, which we then homogenized and filtered to remove bacteria (and larger) sized particles.
Elliot prepares the viral inoculum – which after multiple filtration steps looks clear.
We then heat treated half of the viral inoculum and injected it directly into each of the sea star’s arms. We also took some of the inoculum for later molecular work and to check for the load of SSaDV we were adding. Fingers crossed it actually does have the virus in this inoculum!
Over the next few weeks we’ll be monitoring the health status and microbiology of these test stars, in the hope that those treated with the viruses show signs or symptoms. Previous work has shown that they should do so in 6 – 7 days. We’ll keep our fingers (and arms) crossed!
Ru looks unimpressed after being injected with heat-treated viruses.