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When it comes to the natural world, I have always found myself drawn to things that are unfamiliar and strange. I think that's why I gravitated towards the marine invertebrates: they are the animals most unlike us in just about every way imaginable. Even so, some of them have bodies at least that are recognizable as being both: (1) alive; and (2) animal-ish. Think, for example, of a lobster and a snail. Each has a head and the familiar bilateral symmetry that we have. Obviously they are animals, right? I, of course, am most fascinated not by these easy-to-understand (not really, but you know what I mean) animals, but to the cnidarians and the echinoderms. And for different reasons. The cnidarians astound me because they combine morphological simplicity with life cycle complexities that boggle the mind. I hope to write about that some day. Today's post is about my other favorite phylum, the Echinodermata.

For years now I've been spawning sea urchins, to study their larval development and demonstrate to students how this type of work is done. I have a pretty good idea of what to expect in urchin larvae and can claim a decent track record of raising them through metamorphosis successfully. Urchins are easy. To contrast, I have much less experience working with sea stars. I have found that some species are easy to work with, while others are much more problematic. Bat stars (Patiria miniata), for instance, are easy to spawn and raise through larval development into post-larval life. Ochre stars (Pisaster ochraceus), on the other hand, go through larval development beautifully, but then all die as juveniles because nobody has figured out what to feed them. I've already chronicled my and Scott's attempts in 2015 to raise juvenile ochre stars in a series of posts starting here.

Sea urchins and sea stars have long been model organisms for the study of embryonic development in animals, for a few reasons. First, many species of both kinds of animals are broadcast spawners, which in nature would simply throw their gametes out into the water. This means that development occurs outside the mother's body, so biologists can raise the larvae in the lab and observe what happens. Second, spawning can be induced by subjecting the parents to nonlethal chemical or environment stresses. Third, the larvae themselves are often quite happy to grow in jars and eat what we feed them. Fourth, the larvae of the planktotrophic species are often beautifully transparent, allowing the observer to see details of internal anatomy. Lucky me, I've been able to do this several times. And it never gets old.

All that said, there are differences between urchins and stars that force the biologist to treat them differently if we want them to spawn. For the species I work with, spawning occurs after I inject a certain magic juice into the animals' central body cavity--urchins get a simple salt solution (KCl, or potassium chloride) and stars get a more complex molecule (1-MA, or 1-methyladenine). The fact that you can't use the same magic juice for urchins and stars reflects a fundamental difference in gametogenesis and spawning in these groups of animals.

Female (left) and male (right) spawning purple sea urchins (Strongylocentrotus purpuratus)
20 January 2015
© Allison J. Gong

Sea urchins will spawn only if they have fully developed gametes. In other words, gametogenesis must be complete before gametes can be released to the outside. You can inject as much KCl into a sea urchin as you want, but if it's the wrong time of year or the urchin doesn't have mature gonads (due to poor food conditions, perhaps), it won't spawn. I've never investigated the mechanism by which KCl induces spawning in ripe urchins, but here's what I think happens.

When students dissect animals in my invertebrate zoology class, we use magnesium chloride (MgCl2) to narcotize the animals first. A 7.5% solution of this simple salt is remarkably effective at putting many animals gently to sleep, especially molluscs and echinoderms. Placing the animals in a bowl of MgCl2 and seawater causes them to relax and gradually become unresponsive. A longer bath in the MgCl2 puts them to sleep for good.

Given the relaxation effects of MgCl2 on urchins, I suspect that injecting a solution of KCl into the body cavity relaxes the sphincter muscles surrounding the gonopores. This relaxation opens the gonopore, and if the gonads are ripe the mature gametes are released to the outside. As I said above, I don't know for certain if this is how it works, but the hypothesis makes sense to me. It also explains why that I can shoot up a dozen urchins and get none of them to spawn: the KCl might be doing what it normally does (i.e., opening the gonopores) but if the gonads aren't ripe there are no gametes to be released.

For completely different reasons, injecting a star with KCl does absolutely nothing at all except probably make the animal a bit uncomfortable. The KCl may very well open gonopores as it does in urchins, but a star will never have mature gametes, especially eggs, to release in response to this muscle relaxant. This is because at least in female stars, meiosis (the process that produces haploid gametes) isn't complete until the eggs have been spawned to the outside. What, then, is the magic juice used to induce spawning in stars, and what exactly does it do?

The magic juice is 1-methyladenine, a molecule related to the nucleobase adenine, most commonly known as one of the four bases that make up DNA. The nomenclature indicates that the difference between the two molecules is the addition of a methyl group (--CH3) to the #1 position on an adenine molecule:

Chemistry aside, what I'm interested in is the action of 1-MA on the eggs of sea stars. Meiosis, the process that produces gametes, has two divisions called Meiosis I and II. Meiosis I starts with a diploid cell (i.e., containing two sets of chromosomes) and produces two diploid daughter cells; these daughter cells may not be genetically identical to each other because of recombination events such as crossing over. It isn't until Meiosis II, the so-called reduction division, that the ploidy number is halved, so each daughter cell is now haploid (i.e., containing a single set of chromosomes) and can take part in a fertilization event. In a nutshell, the end products of meiosis are haploid cells, all of which ultimately result from a single diploid parent cell.

In female sea urchins, the entire meiotic process is completed before the eggs are spawned, which is why the relaxation effects KCl can induce spawning.

In females of many other animal species, meiosis is arrested for some period of time after the Meiosis I division. For example, this happens in humans: baby girls are born with all of the eggs they will ever produce, maintained in a state of suspended animation after Meiosis I. It isn't until puberty that eggs begin to complete meiosis, one egg becoming mature and being ovulated approximately monthly for the rest of the woman's reproductive life. Sea stars are sort of like this, with the notable exception that a female star will ripen and produce thousands of eggs in any spawning event rather than doling them out one at a time.

One of the really cool things about working with sea star embryology is that I get to see the completion of meiosis after the eggs have been spawned. I know that the gonads have to reach a certain level of ripeness before 1-MA will induce spawning. Reviewing my notes from a course I took in comparative invertebrate embryology when I was in graduate school, I came across the mention of 'polar bodies,' tiny blobs that I remember seeing in just-fertilized sea star eggs but which I have never seen in sea urchin embryos. Then I needed to remind myself what polar bodies are all about.

Remember how there are two cell divisions in meiosis? Well, despite what's shown in the diagram above, each of the divisions is asymmetrical. In other words, each division of meiosis produces one big cell and one tiny cell. The tiny cells are the polar bodies. They are too small to either divide or be fertilized, and generally die on their own. Here's a chronology of what happens. First, a cell divides, producing a large cell and a tiny polar body:

I've x'd out the polar body in red because it cannot divide or be fertilized and will soon die. Then the large cell divides to produce the final egg and a second polar body:

It turns out that in sea stars things get even more complicated. 1-MA acts as a maturation-inducing substance in these animals, effectively jump-starting the eggs that have been sitting around in an arrested state after undergoing Meiosis I. This initiates the continued maturation of the eggs to the stage when they can be spawned. Even now, though, meiosis doesn't complete until an egg has been fertilized, at which point the second polar body is produced. The production of that second polar body is the signal that Meiosis II has occurred, and the now-fertilized egg can begin its embryonic development.

Here's a freshly fertilized egg of Pisaster ochraceus, with the two polar bodies smushed into the narrow perivitelline space between the surface of the zygote and the fertilization envelope:

Zygotes of the ochre star Pisaster ochraceus, showing two polar bodies
25 April 2017
© Allison J. Gong

Sea urchins, remember, do not have polar bodies when I spawn them. That's because meiosis is complete by the time the eggs can be spawned, so the polar bodies have already died or been resorbed by the final mature egg. The photo of the P. ochraceus zygotes was taken within a few minutes of fertilization. Let's contrast that with a photo of a brand new urchin zygote:

Egg of purple sea urchin (Strongylocentrotus purpuratus) fertilized by sperm from a red urchin (Mesocentrotus franciscanus)
30 December 2016
© Allison J. Gong

See? No polar bodies!

All of this is to explain why we can't use the same magic juice to spawn both urchins and stars. Kinda cool when the madness in our method has a biological context, isn't it?

2

As with many things in life, catching a swarm of honey bees is all about opportunity and availability. In other words, luck. Bees swarm in the spring, as the nectar flow and lengthening days result in near-exponential population growth within a colony, and the bees run out of space in their hive. Capturing and rehiving a swarm is one of the best ways for a beekeeper to increase the number of hives in her apiary, for a few reasons:

  1. It's cheap! Darn near free, except for the minor cost of whatever modified box or bucket used to contain the swarm. For example, for a few years we used an ordinary cardboard file box (the type you'd buy for about $2 at any office supply store) with mesh-covered windows as our official swarm catching box. Last year my husband bought a 5-gallon bucket with lid from a hardware store, cut some windows in it and taped on some mesh. It works better than the box, which was falling apart anyways and needed to be replaced. Still super cheap, too.
  2. Swarms come from locally adapted colonies. True, the mother colony that threw the swarm may have originated as a package colony bought from a commercial beekeeper from anywhere in the country, but at the very least it survived the winter here, which hints at potential long-term suitability for this particular location.
  3. Every swarm that is captured by a beekeeper and rehomed in a managed apiary is a swarm that will not turn a neighbor's home/garage/fence/etc. into a hive. In terms of responsible beekeeping, this is a Really Good Thing™. It is much simpler to relocate a swarm than to remove an established colony from, say, inside the wall of a house. Most homeowners don't like being told that in order to get rid of the colony of bees that has taken up residence between the studs in a wall, the wall will have to be cut open to make sure that all the bees, wax combs, and honey are removed.
Ye olde swarm-catching bucket

Until this past weekend it had been an unfortunate spring for us as beekeepers. For the first time in our eight years donning the veil we had lost almost all of our hives over the winter; all of the hives at our house had died, and we were down to 1.5 hives at our second apiary. We had also missed out on a couple of swarm calls, which either came in when we couldn't deal with them or another beekeeper got to the swarm first. One swarm flew off before we arrived to pick them up, ironically as we were on our way down the highway so I could give a talk on beekeeping to the Watsonville Wetlands Watch.

Much of that luck changed this past Saturday, when we got a call about two swarms in a backyard apple tree. Given that it was a sunny morning, we decided to capture the swarms before the scout bees found a new home site and persuaded their sisters to move into it. They were both good-sized swarms, one a bit larger than a basketball and the other about the size of a football.

Two swarms in an apple tree
15 April 2017
© Allison J. Gong

Those streaky blurs in the sky aren't UFOs or dust streaks on the camera lens; they're bees in flight.

The swarms were both about 8 feet off the ground, which puts them nicely within reach of an ordinary ladder. We had brought a ladder with us and the homeowner had one as well, so we could catch both of the swarms at the same time. In the spirit of full disclosure: I can't take any credit for catching these swarms, as I was taking pictures instead of being useful.

Swarm of honey bees in an apple tree
15 April 2017
© Allison J. Gong

Swarm catching is pretty simple when the bees are clustered in a tree like this: You place a box (or bucket or whatever) under the swarm and either shake the bees into the box or cut the branch they're clustered on and lower that into the box. Shaking tends to send a lot of bees into the air, but as long as the queen ends up in the box the rest of the bees will eventually find their way to her. When they're all in the box you close it up and take it away.

The "small" swarm captured into a cardboard box
15 April 2017
© Allison J. Gong

The large swarm went into the bucket:

The "large" swarm going into the bucket
15 April 2017
© Allison J. Gong

We brought the swarms to the apiary. The next step was to pour the bees from the box and bucket into their intended hives. And this is where our luck changed. One of the swarms, instead of settling into our Blue hive boxes, took off into the air. This happens sometimes, when for whatever reason the queen flies and all of the workers go with her. If the beekeeper is lucky they land some place accessible and can be recaptured. This swarm gathered very briefly in the poison oak at the top of a dead coffeeberry bush, then flew away across the street. I was unable to see where they were headed.

The good news was that the larger swarm was much more cooperative and remained in the Purple hive where they were dumped. Joining them in this apiary is the Rose hive, which was a split from one of our downtown hives. The weather on Sunday and Monday was cold and rainy, and today was the first day the bees had a chance to get out and fly. Today (Tuesday) we saw them orienting to their new home. We shouldn't have any rain for the next several days, which will give them lots of time to forage. Swarms are usually primed and ready to go into building mode as soon as they reach their new home, so the queen in our Purple hive can start laying immediately (assuming, of course, that she was the old queen from the mother hive that threw the swarm; if she's a virgin she'll have to go on her mating flights first). It'll be three weeks before we see an increase in the number of bees; in the meantime the population will decline as bees die off due to natural attrition. Thus around mid-May we should start seeing some big orientation events. Fingers crossed!

I seem to have a need to keep investigating seastar wasting syndrome (SSWS) and trying to make sense of what I and others see in the field. I think it parallels my morbid fascination with the medieval Black Death. In any case, I've devised a plan to continue experimenting with one aspect of the potential recovery of one species, the ochre star, Pisaster ochraceus.

The first step of this plan was to collect a few more stars, which I did back in early March. For the past year or so the stars had been becoming more abundant at certain sites, leading to hope that the populations were beginning to recover and speculation as to whether these individuals were pre-SSWS survivors or post-SSWS recruits. I think they are survivors, because it seems highly unlikely that a star can grow from teensy (a few millimeters in diameter) to hand-sized on a few years. This is what I want to address experimentally in the lab.

The three stars that I collected seemed to adjust well to life in the lab. They all ate well and were crawling around in their tank. Then, last Friday (31 March 2017, to be exact) I checked on the stars as I usually do and was horrified to see this:

Dismembered bits of an ochre star (Pisaster ochraceus)
31 March 2017
© Allison J. Gong

Knowing from experience how quickly this can happen, I'd guess this star had begun ripping itself into pieces in the previous 24 hours. And meantime, its tankmates had stuck themselves to the underside of the cover of the tank. This is not unusual behavior and once I poked them both to make sure they weren't getting mush I decided not to worry about them for the time being. The important thing was to remove the not-dead-yet pieces of the exploded star and bleach the tank before returning the apparently healthy stars to it.

One of the most horrific aspects of SSWS is that it is both blindingly fast and agonizingly slow. It appears to strike out of the blue, by which I mean that stars can look absolutely fine one afternoon and be torn to bits the next morning. And it's slow because the individual pieces can live for hours or even days before finally dying.

31 March 2017
© Allison J. Gong

This star broke itself into five pieces. The three pieces of arm had started getting mushy but still responded by sticking harder when I picked them up. That larger section with two arms and the madreporite was actually walking around the bowl. The torn-off pieces were all oozing sperm into the water, so at least I know this individual was a male. Small comfort, that, when I had to bag up the pieces and throw them in the trash.

Being confronted with the specter of SSWS, I wondered exactly what it meant. I've never been under the illusion that SSWS goes away entirely. I suspect that it is always present in the wild, possibly at low enough levels that we don't notice it for decades at a time. Seeing one dead star, which presumably was infected in the field before I brought it into the lab. . . does it mean the plague is rearing its ugly head again? Or is this a one-off that I just happened to catch? There's only one way to find out, and that is to see if there are more sick stars in the field. So that's what I did the following two days. I had planned to visit three intertidal sites where I expect Pisaster ochraceus to live, but my concussed brain allowed me to drive to only the two nearest sites.

I went to Natural Bridges on Saturday, where I'd been seeing lots of ochre stars over the past several months. I hadn't seen a sick star there for years, although at the outbreak of the plague in 2013 the ochre stars disappeared suddenly. In the past couple of years I'd been happy to see lots of healthy hand-sized stars there. Last weekend it seemed I saw fewer stars than I had gotten used to seeing, but none of them were sick. Whew!

Pair of healthy Pisaster ochraceus at Natural Bridges
1 April 2017
© Allison J. Gong

The next day I went to Mitchell's Cove, where I'd collected those three stars back in March. I did see lots of great-looking stars, some as small as ~6 cm in diameter and others bigger than my outstretched hand.

Trio of healthy Pisaster ochraceus at Mitchell's Cove
2 April 2017
© Allison J. Gong

But I also saw this:

Arm of a P. ochraceus that was killed by SSWS at Mitchell's Cove
2 April 2017
© Allison J. Gong

This is all that remains of an ochre star that apparently succumbed to SSWS. No other body parts are visible in the vicinity, and this arm bit was barely hanging on to the rock. Given how quickly stars can disintegrate when SSWS hits, this one probably began showing symptoms the previous day, while the tide was in and nobody would have seen it. And who knows how many other stars got sick and died without anybody noticing.

The take-home message is that I need to not let SSWS fall off my mental radar. I hope to god that my six remaining P. ochraceus in the lab remain healthy and that I can spawn them in a couple of weeks. I've obtained from a friend some small dishes seeded with food that tiny juvenile stars may be able to eat. I'm not too worried about getting through the larval development stage, although I probably shouldn't get too cocky about that. In any case, it's the post-larval juvenile survivorship that I'm really interested in. This year I don't have Scott to help me with the husbandry and data collection. I will instead be working with another colleague, Betsy. We have a spawning date at the end of April, when the next phase of my ongoing SSWS investigation will begin.

1

As spring arrives in full force, the algae are starting to come back in the intertidal. The past two mornings I went out on the low tides to look for something very specific (which I did find--more on that later) and noticed the resurrection of the more common red algae. So early in the season the algal thalli are nice and clean, not yet having been fouled or munched. And, like all babies, they're pretty dang cute.

Here's a little clump of Endocladia muricata, a red alga with the common name 'scouring pad alga.' I've also heard it referred to as 'pubic hair alga,' by a former instructor of marine botany who shall remain nameless.

Endocladia muricata growing on the test of the large barnacle Tetraclita rubescens, at Natural Bridges
1 April 2017
© Allison J. Gong

What I tried, and failed, to capture in this photo is that the strands have little thornlike extensions that give them the texture of . . . a scouring pad. Here's a better picture of a larger clump, and if you squint you might be able to see what I'm talking about.

Endocladia muricata
1 April 2017
© Allison J. Gong

And here's another baby red, this gorgeous little piece of Plocamium. When they're young like this the branching structure is easier to see. And isn't that color splendid? Especially with the green of the fresh young surfgrass.

A baby Plocamium, growing among the surfgrass Phyllospadix scouleri
1 April 2017
© Allison J. Gong

What I was really thinking about this morning were the morphological similarities that can make it very difficult to distinguish between different species. For example, there are three species of rockweeds that are common around here: Fucus distichus, Silvetia compressa, and Pelvetiopsis limitata. Rockweeds are brown algae but are usually olive-green in color, and live in the high mid-intertidal above the mussel zone. In some places all three species occur together. Fucus (see below) is easy to recognize because its blades are wider and somewhat straplike, with prominent midribs. When Fucus is reproductive the tips of the blades become swollen and full of a gooey mucilage, which contains the gametes. There are other interesting things about sex in Fucus, and at some point I may address those in a later post.

Fucus distichus, a rockweed, at Franklin Point
17 July 2017
© Allison J. Gong

The other rockweeds, Silvetia and Pelvetiopsis, are a lot more difficult to distinguish. They both have less straplike blades. They share a generalized dichotomous branching pattern, but in neither is it as consistent as it is in Fucus.

Pelvetiopsis limitata at Mitchell's Cove
2 April 2017
© Allison J. Gong
Silvetia compressa at Mitchell's Cove
2 April 2017
© Allison J. Gong

 

 

 

 

 

 

 

 

 

This morning these two specimens were growing side by side. In terms of scale the overall length of Silvetia is about twice that of Pelvetiopsis. Keeping that in mind, what you can't tell from these photos is that Silvetia is also coarser and stiffer, like pasta that is about a minute short of being cooked al dente--not hard, but still more firm that you'd probably like it to be. Pelvetiopsis, on the other hand, is rather soft and much more flexible.

If I were to ask you to contrast these organisms based solely on the photos above, you might say that Silvetia looks somewhat less orderly than Pelvetiopsis. And you would be right! The almost-but-not-quite-dichotomous branching in Silvetia doesn't always occur in the same plane, resulting in a thallus that doesn't lie flat. Look at this:

Silvetia compressa at Mitchell's Cove
2 April 2017
© Allison J. Gong

See how those branches, especially the terminal branches, don't all come off in the same direction? That's what I mean. A cross-section of Silvetia's blades would be somewhere between flat and cylindrical, also contributing to the tendency of this thallus not to lie flat. This means that when you press it it does get a little mashed looking.

Pelvetiopsis, on the other hand, is a much more regular beast. The blades are distinctly linear in cross-section and generally branch in one plane. One other thing to note is that in Pelvetiopsis the terminal branch tips are very short relative to the overall thallus length compared to those of Silvetia.

Blade tips of Pelvetiopsis limitata
2 April 2017
© Allison J. Gong

A fair question to ask is: How can you tell the difference between a baby Silvetia and a full-grown Pelvetiopsis? Absolute size might not be a useful characteristic, but the other morphological traits are. The branching orientations and overall blade shapes are fairly consistent throughout the size range for each species. Consistent enough, at least, to make a good gut-level first ID guess.

I wanted to write about this because I saw the organisms, checked them off in my head, and then backed up a bit. I found myself second-guessing my instincts when it came to identifying these specimens. I mean, I know these organisms. Or, I think I do. It's frustrating to look at the creatures I see regularly in the intertidal, organisms whose names I learned many years ago (even through the inevitable taxonomic name changes), and say to myself, "Wait a minute; is that right?" This led me to seriously consider these two rockweed species and evaluate what I really know about each of them. How do I know that one specimen is Pelvetiopsis, when it looks a hell of a lot like a baby Silvetia? I think this unusual self-doubt has to do with post-concussion syndrome. For the past several months I've known that words fly out of my mind as I'm trying to recall them. Why not names as well? At this stage in my recovery I'm supposed to be slowly challenging my brain as well as continuing to rest it. Finding that balance has been tricky. In a few weeks I will have my early morning low tides back. It will be easier for me to drive to intertidal sites then, and I'm going to use tidepooling as therapy. It has been good for my soul in the past, and I hope that it will also be good for my brain in the near future.

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