Tonight at 11: Sea Star Wasting Disease Culprit Caught Red Handed! OR Tune in next week to find out!

Ok, so, unless you've been living under a rock in the marine world for the past 24 h, you'll no doubt have been informed that the mystery of sea star wasting disease (SSWD) has apparently been solved (1). Srsly, it's already in the Wikipedia entry for Sea Star Wasting Disease, get with the program. For those of you who would like a reminder of what SSWD is and why we care: as you wish(2).

This is why we care, because I almost stepped in a gross pile of sea star.
December 3, 2013, Shilshole marina. Evasterias troschelii(?)

Are we all caught up now?

Good because it turns out that it might not be as simple as we would want. This weekend, I spent a few days at a conference, and while in the past I have complained of SCAD, this year, I've really been enjoying the conferences I've been to (more to follow?). I saw a talk this weekend presenting additional data that will soon be published complicating the story. 

But first, let's see where we are: 

The Hewson et al. paper that is receiving so much attention this week appears in an early edition of PNAS, showing a bunch of evidence that this densovirus(3) is associated with the collection of symptoms known as SSWD, e.g., melting, wayward errant arms, complete disintegration of the body within 24 hours of first showing symptoms(4).

Here is some of the evidence the authors are presenting:

1. Researchers took infected individuals, mashed them up, then filtered the diseased mash through a filter with extremely small holes, designed to only allow particles as small as viruses to go through.  Then they took the virus slurry and heated some of it to very high temperatures, which should cause the DNA in the viruses to break apart.  Then they injected some asymptomatic sea stars with the heat-shocked virus slurry (which was subsequently cooled), and some with virus slurry that hadn't been heated. Stars that got the unheated slurry got sick, stars that got the heat-shocked slurry did not. 

• What this means: This shows pretty clearly that a virus, one that is susceptible to heat damage, causes SSWD.

2. Researchers took tissue samples from infected and uninfected stars (total of 28 stars) and looked for whatever virus DNA they could find. Then, after characterizing as many of the viruses as they could, the looked at whether any of the individual viruses was more common in infected stars than uninfected ones. The densovirus they currently attribute to SSWD appeared in 7 of 15 symptomatic stars, but only 2 of 13 asymptomatic ones.

• What this means: A single densovirus was more associated with the symptoms of SSWD in this sample of seastars. 

3. Having a guess about the thing doing the stuff allowed researchers to follow up with a bunch of experiments looking at the amount of the virus (viral load) present in symptomatic versus asymptomatic individuals. They measured viral load in a bunch of  stars collected from the field, and found that, generally, the stars that already look messed up have more of the densovirus in them, BUT asymptomatic stars also contain virus.

• What this means: Having more virus means a star is more likely to be showing symptoms of SSWD. However, the fact that stars that look just fine also have a non-trivial viral load is a bit tricky to interpret. It could be that they are incubating the virus and haven't started to show symptoms, it could be that they are resistant and the virus doesn't cause disease progression in that individual. It could also be that something else causes SSWD that makes stars more vulnerable to this densovirus (5).  

Ok, there's a bunch of other fun data in the paper as well, which makes excellent leisure reading. I suspect no disease of non-commercial marine invertebrates has ever received this much attention. 

Now to the caveat that started this post:

It's a lesson in ecology that as soon as you think you have a story, the next thing you do almost always blows your theory to bits.

Ben Miner gave a talk this weekend at the Western Society of Naturalists Annual Meeting in Tacoma (one of about 40 on SSWD), and showed new data that will soon be published that thicken the plot. Similar to the data shown in the PNAS paper (which he also co-authored), Ben took samples from stars and had them measured for viral load.  However, rather than calling them symptomatic/asymptomatic at the time of sampling, he watched each star for several weeks after the sampling. This way, any infections that were incubating would not be erroneously called "asymptomatic". It turns out when you look at the sea stars this way, the densovirus load is quite a bit LOWER in individuals that ultimately end up with SSWD. 

Well, shoot. Was the previous association of viral load with symptoms just a fluke? Is there another possible explanation? Too soon to tell! 

Science isn't a romance novel that ends all tidily with the one person cozily ensconced (in the PG version) in the other person's arms (trying to avoid being heteronormative here). Science is like one of those radio serial cliffhangers, where you have to "TUNE IN NEXT WEEK to find out how our heroes get themselves out of this jam!" The joy of science is that it is iterative, and this paper represents a substantial advancement of the knowledge on this disease which has been stymying scientists for nearly two years now. We can only wait with baited breath until the next installment!

References and Miscellany:

(1) Actually if you've been living under a rock in the marine world, you might have SSWD, check with your Dr.  (*Editorial Note: J/K, people don't get SSWD, our arms don't walk away like that)

(2) Christmas present to Emily?

(3) This virus is in the Parvoviridae family - which also includes canine parvovirus, to bring it back to something some of us might be able to use as a reference point)

(4) You know, things that generally suck when they happen to you.

(5) But, for the love of God, not radiation from Fukushima-Daichi. If anyone puts this forward as a serious suggestion, I have nothing left to say to you.

Yellow-Bellied Snails OR MORE SNAIL MAIL!!!

Ground Control to Major Emily.

Yeah, Ground Control. Go ahead.

Uhhh, you still doing science out there, Major Emily? 

Sorta, Ground Control. It's complicated.  

...


Well here's some snail mail. New arrivals from Georgia (Fig.1)!

Figure 1. I do declare! Southern snails! We share a love of sitting on the porch drinking mint juleps.

These snails just completed an amazing transcontinental voyage (and, boy, are their arms tired! Just kidding, they don't have arms). Like other molluscan mavens of aviation described on this blog, these guys know how to travel in style - which is to say in a plastic bag, in a cooler, in a box. These are Atlantic Oyster drills from Savannah, Georgia, which are being temporarily re-homed in quarantine in Washington State(1) while they await their opportunity to teach Science amazing things about assessing risk in new situations.

You might recall the Christmas-that-Emily-Ruined Special(2), well it turns out this is the snail I was actually talking about. When I collected this species from the invasive population here in Washington (Fig. 2), those snails stopped eating and hid when they smelled chemical cues from their injured friends - they didn't even need to smell the crab that was eating those friends. They just knew that something was wrong and beat it out of there. It turns out this response is common among invasive snails here, but not seen in native snails(3).

Figure 2. The author, ca. 2009, collecting invasive Urosalpinx cinerea from Long Island, Willapa Bay, WA.

So the question becomes, are these snail species better than our local native snail species at becoming invasive because they listen to their friends when their friends are in danger? That is, do the snails back at home, in Georgia and Massachusetts, also run for their lives when they hear their friends calling for help?  Or, did the pioneer Atlantic Oyster Drills, who left their cozy homes almost 100 years ago on a railroad car headed west to an unknown destiny, in search of a land of endless undespoiled mud to roam, act basically the same as our local native snail species, and natural selection has changed the behavior of the population.  It's possible that the snails that were, quite literally, dumped from the railroad car on arrival, were all basically clueless about the predators in Washington, but some of the snails in that group did run and hide when they heard their friends calling for help when the native predators did attack - and that those snails were the only ones that survived out of the initial emigrees. They were the only ones who could reproduce, and now we have a population where that is the default response.  

Was the invasion caused by snails that listened to their scared friends, or did it result from the invasion that we now have snails that heed the warnings of other snails?

Yellow-Bellied Snails: Invasion Drivers or Survivors?

Since no one back in the early 1900's thought to do the same experiments I have done on the source populations for our invasive snails, and because the logic of time travel makes my head hurt, I'm going to do what is called substituting space for time. If we assume that there has been relatively little change in the Georgian and Massacusettsian (?) snails in the last 100 years(4), we can compare modern east coast snails (in skinny jeans, on their iPhones) to the invasive west coast population. We would predict not only that the Washington population would be more passive-aggressive, but also that they would respond similarly to the east coast snails if running away from cries of help is an invasion driver, or they would respond differently if running away was a trait that was only helpful in the new Washingtonian waters.

Ergo the snails from Georgia, now to keep my fingers crossed that the Masshole snails will make an appearance.  

Fig. 3. Snails from native and non native populations could demonstrate a variety of hypothesized responses that may or may not be related to their native culture and geographic origin.

References and Miscellany:
(1). Don't worry folks, I've got a permit and a lot of bleach and I know how to use 'em.
(2). Specifically Act II, Scene 1.
(3). More on that at some point - it's not really ready for showtime.
(4). This really only applies to the assumption that the selection for response to injured conspecifics hasn't changed, of course there have been other changes. If there have been, for instance, predators that have invaded on the east coast (cough cough, european green crab, I'm looking at you) east coast snails might also have evolved a strong response to injured conspecifics by the same mechanism of the snails that are invasive here. Actually, now that I think about it, that's one good reason to compare snails from both Massachusetts (where the Green Crab has invaded) AND Georgia (where the green crab has not invaded)

Musuem Missive #2 OR A Conchologist's Conch

Is anyone on this earth as behind the times as I am? Seriously! I get a fair amount of ribbing for the fact that I still listen to music that came out when I was in college (but seriously you guys, The Strokes are STILL relevant!). Frankly, this is not news to me. In high school I was also listening to music from the previous decade (The Cure transcends definition by a single era!).  

But I do feel like I should have at least half a clue about things in shells. 

WRONG! 

You guys all probably knew about this, but I was all like whaaaa?

Figure 1. Xenophora, the Conchologist of snails

That's right, do you need me to repeat it?

Figure 2. Xenophora pallidula. Le sigh. P.S. All these pictures are going to be from Hipstagram.
Sorry, I only had my phone and the room only had fluorescent lighting.

If your jaw hit the floor, or your hand hit your forehead - you are correct!

So this is a family of snails(1) called Xenophoridae (= "foreign carrying").  Hoarders, that's what they are. I saw them when I was with the PNWSC touring the Burke Museum's malacology collection (old news).

My fingers are literally doing the equivalent of sputtering on my keyboard - I have so many things in my head, none of them can get out effectively! Ok, ACTIVATE BULLETS!

• Why is this?
• Do individuals have different preferences? Species? Or is everything just collected randomly??
• Why is this?!
• OOOH! You could do a really cool exploration of community change over time for these habitats, just using museum and private collections of these shells and looking at what other species are attached! These are extensively collected species because they are such a curiosity. And I bet the collection records are pretty good!
• WHY is this?!

Ok, a literature search yielded basically nothing - so those of you looking for cool master's projects to do that involve warm water diving - YOU'RE WELCOME!

A little cruising around the internets yields several possibilities, and one certainty.

First, the certainty: Deep Sea News is on top of their business, and posted this a while ago (see the first paragraph).

Now the two possible explanations I've heard of so far for why this is a thing:

1. Behavioral defense
2. Mobility

Behavioral Defense

The defense idea goes like this: Snails make it harder for predators to eat them by increasing their size AND making their shells stronger without wasting energy making a lot of new shell. I buy the size argument more than the strength argument. Lots of aquatic things do this like Daphnia with their rad goth neck wear. This makes sense in many aquatic places where fish are the scariest predators because fish can typically only eat things they can fit their mouth around (gape limitation). But what about crabs? Crabs eat snails (as you are painfully aware of if you have been reading this blog), and probably won't find this shell expansion much of an obstacle(2).

Alternatively, it might be a camouflage in shallower, clearer parts of their habitat. See the video below of Xenophora conchillyophora habitat, and you decide.

To be able to say anything about this, it would be helpful to know what actually preys on this snail in real life (in addition to fascinated humans, of course). If its all fish, then this makes sense to me. Fish are also visual predators, so camouflage would also make sense. So let's just do some cool experiments you guys! Tether out some decorated and minimalist snails and lets see how they do!(3) 

Mobility

It is reported (here), and I admit I cannot personally vouch for this having not experienced it firsthand, that the habitat of these snails is very muddy. By adding easily available shell material in a spiral fashion they increase their shell circumference without having to increase body size. The shell then works like a snowshoe keeping the snail from sinking in the mud. 

I don't have a good intuitive evaluation of this notion (WHAAAT? No arm waving?! Are you feeling OK, Emily?!). OK fine: the logic seems a little shaky to me. Even most large snails are pretty good at navigating through and on top of mud using their foot as a snowshoe. It doesn't seem very necessary to spend so much energy attaching shells to use their shell as a snowshoe, because that means their foot, which is the part that they need to move around, can't get purchase. So how to they get out of a situation like that?

Either, way. SOMEONE DO SOME EXPERIMENTS ALREADY!

Also I bet you're ready for some more pictures by now!

Figure 3. The snail shell you see on the bottom is not the actual snail
featured here under all that debris, but it's just as large! Also check out the bottle cap (left).  

Figure 4. This one looks wave-swept. Actually, I wonder if you can say
anything about the flow environment looking at radial versus directional orientation of their collections?

• Also how? How do they attach it?

Again, no literature, but read this quote from a defunct geocites enthusiast website:

"Characteristically, the shell is covered with other shells, shell fragments, coral pieces, or stones that are attached or cemented with secretions from the animal. The shells are attached dead, although there is one account of a live kitten's paw being attached in an aquarium. All bivalves and bivalve pieces are attached inner side up and gastropods are usually attached with the aperture up. Once an object is selected, it is cleaned (as is the site of intended attachment), and then the object is rotated and fitted to the attachment site. This may take up to 1 1/2 hours. The piece is then held in place with the animal's foot, snout, and tentacle bases and glued into place. The Xenophora may then lay motionless for up to 10 hours, only rocking in place now and then, seemingly a check on the strength of its new attachment." (4)

10 hours?! That's a lot of time spent out of commission to glue a shell or bottlecap into place.  Must be worth it for some reason!

REFERENCES & MISCELLANY:

(1) You will recall from your pneumonic that (F)amily is above "Good Spaghetti"

(2) In fact it might make it easier for them to manipulate by giving them little claw-holds, rounder shells are harder to just out and out crush (Bourdeau 2009 Ecology).

(3) To anyone who actually wants to do this, I am an expert at tethering snails - I have tethered literally hundreds in the last two years. And I have a valid passport and drivers license, just sayin'.

(4) Zymoglyphic took this from a now-defunct (shocking) geocites enthusiast page. 

Museum Missive #1 OR Reports from the bowels of the Burke

The Burke Museum was recently gifted a 100,000 piece shell collection - the Nudelman collection named after the donor. 

One HUNDRED THOUSAND shells.  

I don't have that many of anything, let alone rare natural history artifacts.

So, who better to tour this testament to obsession with natural beauty (slashImeanawesomeshellcollection) with with than people who know a thing or two about shells?!  I had the chance to join the incredibly well-informed folks at the Pacific Northwest Shell Club.  I might know a thing or two about snail behavior and ecology, but dang, these people know their shells!  The word "encyclopedic" comes to mind. 

***Insert soapbox here about how systematists are a dying breed! and how I am a part of the problem***

Ok but even though I knew only vaguely what I was looking at, I felt like a kid in a candy store! Like I was tiptoeing through the tulips.

Here are some pictures. I will apologize in advance that they are all Hipstagram, but I only had my phone with me and the light was terrible in there:

Commence slideshow!

Figure 1. Stellaria solaris. Just ....  there is nothing. 

Figure 2. Onustus exutus (accepted name: WoRMS). 

Figure 3.  This exists.  Did you know that?
I actually forget what it is (why I will never be a good collector)

Figure 4. There were just drawers full of theses things,
 and then boxes that hadn't even been opened yet.

I think 6 years of working with ugly little mud snails really has primed me to just gawk at these things. Really, I could just sit there and sigh all day.

Figures 1, 2, and 4, are species from the family Xenophoridae - which I will feature in a coming post, because, as I've hinted at in FIgure 4, they do cool stuff with calcium.

Today's melodrama: California Sea Hare OR Official Selection for the RRRFF

On my holiday walkabout this year, I happened to end up back at Crystal Cove in Southern California on a reasonable low tide. After availing myself of the local fare (date shake!), we ran some in situ experiments in the natural experimental tanks (tide pools).  

It turns out that local grapsid crabs (Figure 1) do like to eat smashed up mussels, and sea stars (Figure 2) do frighten snails. I'm still a kid messing around with earthworms, really. I think all ecologists are.

Figure 1. Pachygrapsus crassipes. Denizen of the CA tidepool and
comparable in size to a chicken nugget.

Figure 2. Terror of west Coast tidepools (Pisaster ochraceus).
Are you noticing a theme here, yet?

Southern California coasts are pretty different from the PNW, and more diverse, so it's always fun to see new things. The tide was low enough we also saw a handful of sea hares! Sea hares are nudibranchs, which I'm used to thinking of as being quite small. I wasn't fooled into thinking they were red algae, but these were so big (6-8" long) that there was a very brief moment when I thought I was looking at a sea cucumber. 

So, like any good wannabe documentarian, I took shaky video with my phone. Today, because I evidently felt like I had done enough work, I strung together the few clips that didn't have my fingers in them. Feel free to witness the resulting oeuvre, which the critics are calling:

 ...at best, a clumsy demonstration of the flattening powers of Imovie!  ...

 ...so wobbly, I tossed my cookies!...

...more overblown gangrene than my telenovelas...  

and featuring my first efforts at "editing" sound. Sir David better look out for his job!