Dinner time!

Posted on by Allison J. Gong

The red-tailed hawk parents across the canyon are being kept busy by their hungry chicks. This year they have a trio of youngsters to feed–last year they successfully fledged two chicks–but apparently they’ve not had any trouble finding enough food for all three of them. If I had the luxury of staying home all day to watch hawks I’d probably get to see several feedings throughout the day. As it is, most days this week I’ve been able to watch a late afternoon feeding when I come home.

The chicks are now big enough to thermoregulate on their own, and quite often will be left in the nest alone for extended periods. The other day when I was home for lunch I happened to see the mama hawk fly up the canyon and alight in a pine tree close to my house. A quick check of the nest showed that the chicks were sleeping (I didn’t see any fuzzy lumps above the rim of the nest) so I concentrated on the mom and was able to take this photo:

Female red-tailed hawk (Buteo jamaicensis), taking a break from nest duties. 13 April 2016 © Allison J. Gong
Female red-tailed hawk (Buteo jamaicensis), taking a mid-day break from nest duties.
13 April 2016
© Allison J. Gong

All told she was away from the nest for about 15 minutes. She basked in the sun, did a bit of preening, and spent quite a lot of time looking down (I assume for prey on the ground). A raven and a pair of Anna’s hummingbirds tried to engage her in some extracurricular activity, but she ignored them.

This afternoon I got home at about 17:30 and went out back to check on the nest. Turns out I made it home just in time to view the evening feeding. One of the parents, I couldn’t tell which, was feeding the chicks long bloody strips of some mammal that had gray fur. All three chicks were fed. Here, see for yourself:

The chicks are growing real feathers now and look like awkward pre-adolescents. They’ve lost the cuteness of the fluffy baby stage and haven’t yet attained the badassness of their parents. In fact, right now they’re downright ugly. In the next couple of weeks they’ll start looking like punky teenagers as their feathers continue to come in. They’ll also spend more time walking around the nest.

Oh, and by the way, the nest is attracting flies now. Good thing birds don’t have a keen sense of smell, because it’s gotta be pretty stinky up there, what with all the bird poop and rotting bits of previous meals. Also good (for the humans in the neighborhood) that the nest is about 100 feet above the ground.

What are they up to?

Posted on by Allison J. Gong

These sand dollar (Dendraster excentricus) larvae that I’ve been raising will be 21 days old tomorrow, and they are still on the fast track. They’re developing much more quickly than any of the sea urchin cohorts I have raised. Some of them already have juvenile rudiments with tube feet visible. With the urchins (Strongylocentrotus purpuratus) this is the age when I worry about the cultures crashing for no apparent reason, and so far these sand dollar plutei look great. I hope I didn’t jinx them by writing that. In any case, the sand dollars are known to go through larval development more quickly than their sea urchin cousins, so my larvae appear to be playing by the book, at least as far as timelines go.

Just for kicks I took the largest full-sib cohort I had and split it into two batches. One batch I’m feeding the recommended combination of Rhodomonas sp. (red) and Dunaliella tertiolecta (green), and the other I’m feeding Rhodomonas sp. only. I’ve been able to raise urchin larvae through metamorphosis on a diet of Rhodomonas so I assumed that this food might work for the sand dollars as well. It turns out, however, that the Rhodomonas-fed larvae look a little strange now.

Pluteus larvae of Dendraster excentricus, age 19 days. 11 April 2016 © Allison J. Gong
Pluteus larvae of Dendraster excentricus, age 19 days.
11 April 2016
© Allison J. Gong

Their bodies have become more opaque and compact; they’ve shrunk to a length of 450-500 µm. I wonder if this is the first stage in metamorphosis. I didn’t see a well-defined juvenile rudiment in any of the larvae I examined but that doesn’t mean it isn’t there. And although they look weird and deformed, they don’t necessarily look bad. They just don’t look . . . right.

On the other hand, there may indeed be something wonky going on. I have a jar of siblings of these larvae being fed a red/green diet, and they look totally different.

Pluteus larvae of Dendraster excentricus, age 19 days. 11 April 2016 © Allison J. Gong
Pluteus larva of D. excentricus, age 19 days.
11 April 2016
© Allison J. Gong

This is a beautiful 8-armed pluteus larva. It looks great! The arms are nice and long but none of the arm spines are poking through the ends. They appear to be eating well and have grown to a length of 700-800 µm. This is a ventral view, and that oblong blob on the left side of the pigmented stomach is the juvenile rudiment.

Here’s a close-up view of the rudiment:

Pluteus larvae of Dendraster excentricus, age 19 days. 11 April 2016 © Allison J. Gong
Pluteus larvae of D. excentricus, age 19 days.
11 April 2016
© Allison J. Gong

See how the rudiment is crowding into the stomach? And if you squint you might be able to talk yourself into seeing a couple of round blobs in the rudiment. These would be tube feet, which I can see as I focus the microscope up and down through the animal’s body but which don’t show up very well in a photograph.

The next day that I change the water and have a chance to look at these guys under the microscope is Friday. It’s only three days from now, but given how quickly the larvae are developing, a lot could happen between now and then. I’m a little nervous.

Sexy time for sea anemones

Posted on by Allison J. Gong

This morning I went out on the first morning low tide of the season. I was so excited to have the morning lows back that I got to the site early and had to wait for the sun to come up. Awesome thing #1 about early morning low tides: Having the intertidal to myself.

Dawn over Davenport Landing. 9 April 2016 © Allison J. Gong
Dawn over Davenport Landing.
9 April 2016
© Allison J. Gong

The purpose for the trip was to collect some algae for a talk I’m preparing; I’ll be speaking to the docents at Natural Bridges State Beach at their monthly meeting this coming Wednesday. They invited me to talk to them about algae. I already have a lecture on algae prepared, but last year I set the bar pretty high with this particular audience and want do something a little different. So I’ll talk to them for a bit, show them some of my pressings, and invite them to press a couple of specimens. This morning I collected a few pieces of algae and took a bunch of pictures.

The Anthopleura anemones continue to fascinate me. At Davenport Landing there’s an area where the rock has eroded and forms a sort of channel. In this channel at low tide the water comes about up to my knees. The rock in the channel remains clear of algae but sometimes contains sand. Scattered over the bottom of this channel are several A. artemisia anemones, which can burrow into the sand when it is present. I’ve photographed these animals many times, as they are magnificently photogenic and in deep enough water that I can just stick my camera below the surface and click away.

This morning the first anemone I looked at in this channel had some orange gunk on its oral surface. At first I thought it had latched onto a piece of bleached algae, but then noticed that others had the same thing. My second thought was, “Ooh, eggs!” If I were at the lab I’d have sucked up some of the gunk and examined it under the microscope.

Spawning female Anthopleura artemisia at Davenport Landing. 9 April 2016 © Allison J. Gong
Spawning female Anthopleura artemisia at Davenport Landing.
9 April 2016
© Allison J. Gong

Usually when animals spawn the gametes are quickly dispersed by water currents. But this channel is high enough that at low tide it doesn’t exchange water with the ocean so there are no currents except those generated by the wind. Awesome thing #2 about early morning low tides: No wind. Once I used the camera as a sort of underwater microscope I could see the granular texture of the orange gunk, which told me that these were, indeed, eggs. Cool! Because I was on a hunt for algae I didn’t spend a lot of time censusing these anemones, but I figured that statistically speaking they couldn’t all be females. And sure enough, after a very short search I found some males.

Spawning male A. artemisia at Davenport Landing. 9 April 2016 © Allison J. Gong
Spawning male A. artemisia at Davenport Landing.
9 April 2016
© Allison J. Gong
Spawning male A. artemisia at Davenport Landing. 9 April 2016 © Allison J. Gong
Spawning male A. artemisia at Davenport Landing.
9 April 2016
© Allison J. Gong

So today I learned that April is when the A. artemisia anemones have sex. Makes sense, as spring is the time of year when many organisms (algae and invertebrates) in the intertidal reproduce. Reproduce sexually, that is.

Some animals reproduce clonally as well as sexually, and while sexual reproduction tends to be seasonal, clonal reproduction doesn’t seem to be. Along the coast of central/northern California we have four species of anemones in the genus Anthopleura:

  • A. artemisia, the moonglow anemone (see above)
  • A. elegantissima, the aggregating anemone
  • A. sola, the sunburst anemone
  • A. xanthogrammica, the giant green anemone

Of these four species, only A. elegantissima clones readily. It does this by ripping its body in half in a process called binary fission. The two halves of the animal pull away from each other and the tissue between them gets stretched thinner and thinner until it rips. Then each former-half heals the wound and gets on with life, completely independent of the other. It sounds rather awful but is a very effective way to form clones of genetically identical units that can monopolize large areas in the intertidal.

Anemone (Anthopleura elegantissima) undergoing binary fission, at Davenport Landing. 9 April 2016 © Allison J. Gong
Anemone (Anthopleura elegantissima) undergoing binary fission, at Davenport Landing.
9 April 2016
© Allison J. Gong

It’ll probably take this anemone another day or two to completely tear itself into two pieces. Anemones can continue to clone like this, with each individual splitting into a pair of individuals, for a long time. Eventually this process can form large clones. More about the ecology of these clones in a separate post some time.

Wildflower excursion to southern California

Posted on by Allison J. Gong

Yesterday I joined some friends on an impromptu day trip to southern California to see the spring wildflower bloom. The El Niño rains had brought forth a “superbloom” this year, and while we didn’t have time to go all the way to Death Valley we thought we’d be able to see lots of flowers in closer locations.

Stop #1: Tejon Pass, Tehachapi Mountains

California poppies (Eschscholzia californica) on hillside of Tehachapi Mountains. 2 April 2016
California poppies (Eschscholzia californica) on hillside of Tehachapi Mountains.
2 April 2016
© Allison J. Gong
California poppies (E. californica) on hillside of Tehachapi Mountains.
2 April 2016
© Allison J. Gong

It was interesting to note that we saw poppies only on the south-facing slopes. Wanting to get a closer look we continued on our way.

Stop #2: Cerro Noreste/Hudson Ranch Road above the Maricopa Flats

We stopped briefly in Gorman and got our first close-up look at wildflowers. I got to see my beloved California poppies (Eschscholzia californica), but they were not nearly as abundant as I had hoped.

California poppy (Eschscholzia californica) on roadside hill in Gorman, CA.
2 April 2016
© Allison J. Gong
California poppy (E. californica) on roadside hill in Gorman, CA.
2 April 2016
© Allison J. Gong
California poppies (E. californica) and baby blue eyes (N. menziesii) on roadside hill in Gorman, CA. 2 April 2016 © Allison J. Gong
California poppies (E. californica) and Phacelia ciliata (the purple flowers) on roadside hill in Gorman, CA.
2 April 2016
© Allison J. Gong

The flowers in Gorman weren’t as spectacular as we had hoped, and in the interest of expediency we didn’t take much time to explore a site that didn’t look promising. We crossed I-5 and headed west through Frazier Park and onto the Mil Potrero Highway, which at some point becomes the Cerro Noreste/Hudson Ranch Road. And along this road we saw purple and yellow/orange flowers.

Purple flowers along road in Gorman, CA. 2 April 2016 © Allison J. Gong
Purple flowers along Cerro Noreste Road above the Maricopa Flats, CA.
2 April 2016
© Allison J. Gong
Purple wildflowers along Cerro Noreste Road above the Maricopa Flats, CA. 2 April 2016 © Allison J. Gong
Purple wildflowers along Cerro Noreste/Hudson Ranch Road above the Maricopa Flats, CA.
2 April 2016
© Allison J. Gong

I took some close-up shots of the purple flowers, hoping to be able to identify them when I got home. They’re very pretty! And I was able to determine that they are Phacelia ciliata. They were by far the most abundant blue or purple flowers we saw yesterday.

Baby blue eyes (Nemophila menziesii) in Gorman, CA. 2 April 2016 © Allison J. Gong
Phacelia ciliata along Cerro Noreste/Hudson Ranch Road above the Maricopa Flats, CA
2 April 2016
© Allison J. Gong

Our other orange flower was fiddleneck, Amsinckia menziesii:

Fiddleneck (Amsinckia menziesii) on roadside hill in Gorman, CA. 2 April 2016 © Allison J. Gong
Fiddleneck (Amsinckia menziesii) along the Cerro Noreste/Hudson Ranch Road above the Maricopa Flats, CA
2 April 2016
© Allison J. Gong

Stop #3: Carrizo Plain

Wanting to check out conditions on the Carrizo Plain, we headed northwest on Soda Lake Road. Our first views of wildflowers on the hills looked like they were part of a pastel painting.

Wildflowers on hills of Carrizo Plain. 2 April 2016 © Allison J. Gong
Wildflowers on hills seen from Soda Lake Road, Santa Margarita, CA.
2 April 2016
© Allison J. Gong
Wildflowers on hills of Carrizo Plain. 2 April 2016 © Allison J. Gong
Wildflowers on hills seen from Soda Lake Road, Santa Margarita, CA.
2 April 2016
© Allison J. Gong

On the Carrizo Plain itself, the most abundant flowers were baby blue eyes (N. menziesii) and goldfields (Lasthenia californica). They made large colorful patches on the plain. So pretty!

Fields of goldfields (Amsinckia menziesii) on the Carrizo Plain. 2 April 2016 © Allison J. Gong
Fields of goldfields (L. californica) and Phacelia ciliata on the Carrizo Plain.
2 April 2016
© Allison J. Gong
Fields of goldfields (Amsinckia menziesii) on the Carrizo Plain. 2 April 2016 © Allison J. Gong
Fields of goldfields (L. californica) and Phacelia ciliata on the Carrizo Plain.
2 April 2016
© Allison J. Gong

Goldfields are not called “goldfields” without reason:

Goldfields (L. californica) on the Carrizo Plain. 2 April 2016 © Allison J. Gong
Goldfields (L. californica) on the Carrizo Plain.
2 April 2016
© Allison J. Gong
Goldfields (L. californica) on the Carrizo Plain. 2 April 2016 © Allison J. Gong
Goldfields (L. californica) on the Carrizo Plain.
2 April 2016
© Allison J. Gong
Goldfields (L. californica) on the Carrizo Plain. 2 April 2016 © Allison J. Gong
Goldfields (L. californica) on the Carrizo Plain.
2 April 2016
© Allison J. Gong
Goldfields (L. californica) on the Carrizo Plain. 2 April 2016 © Allison J. Gong
Goldfields (L. californica) on the Carrizo Plain.
2 April 2016
© Allison J. Gong

I had never made a trip specifically to see wildflowers before, and although it was a 16-hour day and my allergies and asthma are horrible today, it was totally worth it. The fleeting spring wildflower bloom is one of the things that makes California special. In a state with a Mediterranean climate, this short period of blatant reproduction before the onset of the dry season is a pretty magnificent thing to witness.

A day in the life

Posted on by Allison J. Gong

Friday 1 April was the last day of my spring break, and tomorrow I go back to teaching. Spring break felt very short this year, and I was busy the entire week. I decided to spend my last day of freedom doing my favorite lab-related things: looking through microscopes at tiny organisms. I had already planned on spending a few hours dealing with my two batches of larvae, and figured I might as well make a day of it and collect a plankton sample on my way in.

It was a beautiful morning out on the bay.

Morning on Monterey Bay. 1 April 2016 © Allison J. Gong
Morning on Monterey Bay.
1 April 2016
© Allison J. Gong

Alas, as gorgeous as the outdoor scenery was, I couldn’t linger long once I’d collected the plankton sample so I headed to the lab. If you’ve ever wondered what a marine biologist’s desk looks like, here’s mine:

My desk at the marine lab. 1 April 2016 © Allison J. Gong
My desk at the marine lab.
1 April 2016
© Allison J. Gong

The dissecting scope on the left belongs to me, as it was a graduation gift I bought for myself when I finished graduate school. The compound scope on the right belongs to the lab, but I’m the person who uses it most frequently. I find that, when looking at something like plankton, it’s easiest to start by looking at a bit of the sample in a small dish under the dissecting scope; then, when I find interesting critters I can pipet them out and put them on a microscope slide for observation under the compound scope. It may seem a little awkward, but this switching back and forth between “forest” and “tree” views works for me. And honestly, any field biologist worth her salt should be able to switch focus from “big picture” to “small detail” fairly easily. How else would she be able to develop a solid understanding of the system(s) she studies?

Now back to the plankton. Right off the bat I could see with the naked eye some big (by plankton standards) crustaceans zooming around. It wasn’t easy chasing them down with the pipet, but after a while I caught one and dumped it on a depression slide. It was a mysid shrimp.

A mysid shrimp collected in a plankton sample. 1 April 2016 © Allison J. Gong
A mysid shrimp collected in a plankton sample.
1 April 2016
© Allison J. Gong

Those big compound eyes are stereotypical of many crustaceans–think crabs, lobsters, large shrimps, etc. Looking carefully at the tail of this particular individual, can you see two small circular structures? Those are statocysts, the organs that give the animal information about its orientation with respect to gravity. The presence of two statocysts in the uropods (the appendages on the most posterior segment of the body) tell me that this animal is a mysid, rather than one of the gazillion other shrimplike crustaceans living in the sea. I saw at least half a dozen mysids in this plankton sample.

Overall, this wasn’t the most interesting plankton sample I’ve ever collected. When my students and I collected and examined a sample a week earlier, we saw much more animal diversity than I saw the other day. We had some strong winds on Monday-Thursday of last week (I’m writing this on Sunday) and the surface water temperature dropped to 12°C; I thought this would be the start of the spring upwelling season. If it was, then the phytoplankers hadn’t responded when I collected this plankton sample on Friday. In any case, it appears that the spring phytoplankton bloom hadn’t yet begun. I expect that in another week or two I’ll find more diatoms in the plankton.

After lunch it was time to tend and observe my larvae. There’s not much to report about the Dermasterias (leather star) larvae. If you remember, I’ve split these larvae into three different food treatments: (1) Dunaliella only; (2) a combination of Dunaliella and Isochrysis; and (3) Isochrysis only. At this point, 38 days into development, there is no discernable difference between treatments 1 and 2. The larvae in treatment 3, however, don’t look so good. They are stunted and appear to be regressing to earlier developmental stages.

On the other hand, the Dendraster (sand dollar) plutei continue to astound and fascinate me. They are stunning!

Pluteus larva of Dendraster excentricus, age 9 days. 1 April 2016 © Allison J. Gong
Pluteus larva of Dendraster excentricus, age 9 days.
1 April 2016
© Allison J. Gong

They are happy and healthy and seem to be doing well. Their posterodorsal arms have grown and their pre-oral arms (the fourth and last pair to form) are poking out. The larvae are eating all the food I’m giving them and are putting it to good use. At this rate I expect to see their rudiments developing soon.

Aren’t plants supposed be green?

Posted on by Allison J. Gong

One of my agenda items for spring break this week was to return to Elkhorn Slough and finish the hike that I started with my students a couple of weeks ago. I got out there only to be forcibly reminded that the visitor center, where the hike originates, is closed on Mondays and Tuesdays. Since I’d driven out there, I figured I might as well poke around the area and see what else would catch my eye. I ended up at Kirby Park, a public access area where kayaks put into the water. The tide was out when I arrived, shortly before noon, and the flats were occupied by foraging birds.

Shorebirds and gulls foraging at Kirby Park. 29 March 2016 © Allison J. Gong
Shorebirds and gulls foraging at Kirby Park.
29 March 2016
© Allison J. Gong

I was able to identify birds that forage in the water (avocets, northern shovelers, cormorants, and grebes) and birds that forage in mud (willets, marbled godwits, yellowlegs, and whimbrels), and there were others that I couldn’t see well enough to ID. I didn’t even really try with the gulls. I do know they weren’t either western or California gulls, but that’s about it. Someday I may be able to tackle the gulls, but with their multiple juvenile plumages they’re a notoriously tough group to figure out.

Many areas of Elkhorn Slough have been invaded by the Japanese mud snail Battilaria attramentaria. This snail was accidentally introduced into the area as tag-alongs on Asian oysters that were imported for mariculture. Battilaria aren’t very big, reaching lengths of about 30 mm, but they can occur in astounding densities. A researcher at the slough has documented how this invasive snail came to be so prevalent, and how it has affected the native California snail Cerithidea californica. From the boardwalk trail at Kirby Park I could look down and see many Batillaria in the exposed mud flat.

The invasive Japanese mud snail, Battilaria attramentaria, on the mud flats at Kirby Park. 29 March 2016 © Allison J. Gong
The invasive Japanese mud snail, Battilaria attramentaria, on the mud flats at Kirby Park.
29 March 2016
© Allison J. Gong

This isn’t a particularly dense group of Battilaria, either. Across the highway towards the ocean there are mud flats that, when the tide is out, appear to be carpeted with wood chips; all the “wood chips” are the shells of living or dead Battilaria.

One of the Slough inhabitants that I find very interesting is the plant Cuscuta pacifica, commonly referred to as marsh dodder. Dodder is a parasitic plant, and at Elkhorn Slough its main host is pickleweed (Salicornia pacifica). Pickleweed is a perennial succulent that dies back in the winter; it is now beginning to regrow into the mounds that will be the predominant plant in the salt marshes of the Slough.

The first time I saw dodder I thought that some clown had vomited a can of orange Silly String over the pickleweed. I still think that’s what it looks like:

Salt marsh dodder (Cuscuta salina) on its host plant pickleweed (Salicornia virginica). 29 March 2016 © Allison J. Gong
Salt marsh dodder (Cuscuta pacifica) on its host plant pickleweed (Salicornia pacifica) at Kirby Park.
29 March 2016
© Allison J. Gong

One of the clues that something interesting is going on with dodder is the orange color. We are used to thinking of plants as being green, or at least green-ish, because they are photosynthetic. Dodder, on the other hand, is a parasite and lives off the tissues of its host; it therefore has no need for chlorophyll, the green molecule that captures light energy used to fix carbon into organic molecules. Looking more closely at the structure of dodder gives you an idea of how it makes a living:

Dodder and pickleweed at Kirby Park. 29 March 2016 © Allison J. Gong
Dodder (C. pacifica) and pickleweed (S. pacifica) at Kirby Park.
29 March 2016
© Allison J. Gong

Dodder consists primarily of orange tendrils that wrap around the host plant. The tendrils penetrate into the vascular tissue of the host and begin withdrawing phloem (the syrupy solution of sugars) from it. Once the dodder has established this internal connection with the host, its own roots die and the dodder becomes entirely dependent on the host. A single plant of dodder can send its tendrils around multiple host plants. From an evolutionary perspective it is impossible to believe that host plants such as pickleweed don’t have defenses against dodder. They may be able to repel the tendrils by producing noxious chemicals, but this is a topic that hasn’t been well studied. Somebody needs to fix that, as inquiring minds want to know.

Dodder (C. pacifica) on pickleweed (S. virginica) at Kirby Park. 29 March 2016 © Allison J. Gong
Dodder (C. pacifica) on pickleweed (S. pacifica) at Kirby Park.
29 March 2016
© Allison J. Gong

Still on the fast track

Posted on by Allison J. Gong

Because I was so surprised at how quickly my sand dollar larvae (Dendraster excentricus) were developing, I checked my notebook from the invertebrate embryology course I took while in grad school to see if what I’m observing now is normal for these animals. It turns out that yes, Dendraster does develop at a much quicker rate than its cousin the sea urchin. And now that I think of it, when I took that 5-week embryology course the sand dollars were the only echinoids that we followed all the way to competence; we spawned and observed urchins as well, but none of them were as far along as the sand dollars by the time the class ended and we “graduated” our larvae off the dock.

Yesterday my Dendraster larvae were five days old. They already had two well-developed pairs of arms and were working on the third pair.

Pluteus larva of the sand dollar Dendraster excentricus, age 5 days. 28 March 2016 © Allison J. Gong
Pluteus larva of the sand dollar Dendraster excentricus, age 5 days.
28 March 2016
© Allison J. Gong

These larvae are big, too–500 µm long. Of course, they started from eggs that were over twice the size of urchin eggs, but they’ve still grown a lot in only five days. The fourth pair of arms will be the preoral arms. At the rate these larvae are developing, I wouldn’t be surprised if these arms show up in the next few days.

As beautiful as those long arms are, they may be a little too long. The larvae swim and gather food using a band of cilia that runs up and down all the arms; the entire body is ciliated, but the ciliated band is the primary locomotory system. I remember the instructor of my embryology course telling us that echinoid plutei will respond to lack of food by growing longer arms, which increases the length of the ciliated band and thus (presumably) the animal’s ability to capture the food that is available. There are two pieces of circumstantial evidence that my larvae may be a little food-deprived: (1) the really long arms; and (2) the lack of visible food cells in the stomachs. In urchin plutei that are feeding well I can see food cells churning away in the stomachs. These Dendraster plutei have beautifully transparent bodies, but I don’t see food in the guts. On they other hand, they are growing, so obviously they are eating. Just in case they are short of food, though, I’ll increase their food ration for the next few days and see how the animals respond.

In the meantime, I continue to be fascinated by the intricacy of the larval skeleton and the complexity of the skeletal rods themselves. Next time I’ll try to take photos of these.

Fast!

Posted on by Allison J. Gong

My sand dollar larvae are developing very quickly! When I checked on them Thursday afternoon about 24 hours post-fertilization, I anticipated seeing them up in the water column because that’s how long it takes urchins to hatch. Remember, sea urchins and sand dollars are in the same taxonomic class (Echinoidea) and share a larval form called the echinopluteus. I’ve watched urchin development often enough that I have a sort of intuitive feel for how it goes, and am subconsciously comparing these sand dollars to the urchins’ time table. I need to stop doing that.

Anyway, on Thursday the sand dollars had indeed hatched. The big surprise was that when I examined them under the microscope I saw that they were much further along than urchin embryos would be at the same age. I expected to see the embryos swimming around as blastulae (hollow balls of ciliated cells); however, these sand dollar embryos had almost completed the process of gastrulation to form their archenteron, or first gut.

Gastrulating embryo of the sand dollar Dendraster excentricus, age 24 hrs. 24 March 2016 © Allison J. Gong
Gastrulating embryo of the sand dollar Dendraster excentricus, age 24 hrs.
24 March 2016
© Allison J. Gong

In echinoids the archenteron develops from an invagination into the blastula. Imagine a balloon. Now imagine poking your finger into the balloon–you’ve just made an invagination. If you continue the invagination across the entire balloon until your fingertip pops out on the other side, you’ve created a tube that penetrates through the balloon. This tube is the archenteron. Interesting tangent: You know that any one-way gut has two openings, right? One is the mouth and the other is the anus. The point in the blastula where gastrulation begins is called the blastopore. The fate of the blastopore is to be either the mouth or the anus of the archenteron. Echinoderms are deuterostomes (“second mouth”), a term that means the blastopore becomes the anus and the mouth is the second opening that forms when the invagination punches through to the other side of the blastula. Yes, sea urchins and sea stars and sand dollars all have an anus before they have a mouth. And guess what? So did you. The chordates, including us, are also deuterostomes.

These sand dollar embryos went from zygote almost to feeding larva in only 24 hours. In fact, some of them may have had mouths when I looked at them on Thursday. I had to start feeding them, so that food would be available as soon as they were able to eat.

Another 24 hours later, on Friday afternoon, I checked on the larvae again and they were bona fide plutei already. They had the cup-shaped body body of the pluteus larva and two pairs of arms, with complete guts. The stomachs in these larvae are huge, occupying almost the entire volume of the main body of the animal. Some of the larvae are also developing red pigment spots.

Early four-armed pluteus larva of Dendraster excentricus, age 2 days. 25 March 2016 © Allison J. Gong
Early four-armed pluteus larva of Dendraster excentricus, age 2 days.
25 March 2016
© Allison J. Gong

See how big and round that tummy is?

And how could I have forgotten that the plutei of Dendraster have fenestrated arm rods??? They are so beautiful! This is the same animal as in the photo above, but I focused in on the skeletal rods in the postoral arms. See the fenestrations in the rods? The larva is about 300 µm long.

Pluteus larva of D. excentricus, age 2 days. 25 March 2016 © Allison J. Gong
Pluteus larva of D. excentricus, age 2 days.
25 March 2016
© Allison J. Gong

For whatever reason, plutei of the local species of sea urchins don’t have fenestrated arm rods. This difference in larval morphology between the two most common echinoid species in the area should make it easy to identify plutei collected in plankton tows. We’re at the beginning of the spring bloom now, and I hope to keep an eye on how the plankton community develops through the spring and summer.

The next day I examine the larvae is Monday. I’ll see if they’re still on the fast track to metamorphosis.

A new obsession

Posted on by Allison J. Gong

This afternoon I met up with Joanna and Amy, who had come to the marine lab with some sand dollars (Dendraster excentricus) to try to spawn. Since sand dollars are in the same taxonomic group (the Echinoidea) as sea urchins, I’d try the same techniques on these animals I’d never spawned before. I did have to modify some things a bit, mostly to account for the difference in body shape between sand dollars and urchins. Urchins are globular, with quite a large internal body volume, while sand dollars are flat. There’s much less space inside a sand dollar for gonads and guts.

Gravid echinoids such as urchins and sand dollars can be pretty easily induced to spawn by injecting their internal body cavity with a solution of KCl. We shot up all eight sand dollars and five of them spawned, two males and three females. One of the males didn’t give enough sperm to be collected, so we didn’t use his gametes. The other male, though, gave us lots of sperm. And they were good sperm, too.

Live sperm of the sand dollar Dendraster excentricus, 400X magnification. 23 March 2016 © Allison J. Gong
Live sperm of the sand dollar Dendraster excentricus, 400X magnification.
23 March 2016
© Allison J. Gong

If you’ve never had a chance to see swimming sperm under a microscope, today is your lucky day!

And the eggs. Wow, sand dollar eggs are freakin’ cool! For one thing, they’re big, ~130 µm in diameter, compared to the 80 µm eggs of the purple urchin Strongylocentrotus purpuratus. Plus, they have a really thick jelly coat that contains red pigment cells; urchin eggs don’t have the pigment cells, either.

Eggs of the sand dollar Dendraster excentricus. 23 March 2016 © Allison J. Gong
Eggs of the sand dollar Dendraster excentricus
23 March 2016
© Allison J. Gong

The eggs themselves were a little lumpy, not as perfectly round as I’m used to seeing with the urchins, but they fertilized just fine. In all three of the crosses, the fertilization rate was 90-95%. Apparently the sperm have no problem digging through the jelly coat to get to the egg surface.

Zygote of D. excentricus. 23 March 2016 © Allison J. Gong
Zygote of Dendraster excentricus
23 March 2016
© Allison J. Gong

In this photo you can see the familiar fertilization envelope raised off the surface of the egg, as well as the red pigment cells in the jelly coat. This may very well be the most beautiful zygote I’ve ever seen. How many people can say things like that?

After an hour and 20 minutes sitting on my desk at room temperature the zygotes started to cleave:

2-cell embryos of Dendraster excentricus 23 March 2016 © Allison J. Gong
2-cell embryos of Dendraster excentricus
23 March 2016
© Allison J. Gong

The blastomeres are still a little wrinkled and lumpy, but I think they’ll be okay. I’ve poured them into 1000-mL beakers and they’re sitting in one of my seawater tables. Tomorrow afternoon I hope to see them swimming up in the water column. Fingers crossed!

Seeing (wannabe) stars

Posted on by Allison J. Gong

So. I have a batch of larvae from a spontaneous spawning of the leather star, Dermasterias imbricata, that occurred four weeks ago tonight. Until now I’ve never had an opportunity to work with this species, even though we have quite a few of them at the marine lab. I had my own for several years, until they became casualties of the plague about a year into the current sea star wasting syndrome event. In any case, this is the first time I’ve been able to spend time with larvae of this species. At the very least I wanted to see how big they would get and how quickly they would develop, compared to the species I’m more familiar with, Patiria miniata (bat star) and Pisaster ochraceus (ochre star).

When the Dermasterias spawned, the first thing I noticed was that the eggs are huge. I measured them at 220 µm in diameter, which is big even compared to what I’ve seen in other stars. Hatch rates were pretty good, and four days later the larvae were already in the 400-430 µm range. Since I have no experience culturing this species, I thought I’d divvy up my larvae and put them into three feeding treatments to see which larval diet resulted in the best overall success. According to the literature, Dermasterias larvae can be raised on a mixture of the unicellular algae Dunaliella tertiolecta (green) and Isochrysis galbana (golden). My three feeding treatments are: Dun only, a Dun/Iso mix, and Iso only.

A week into the experiment there was a clear difference between the larvae eating only the green food, and those eating either a mixture of green and golden or only the golden. Larvae from all food treatments were about the same size, but the ones eating only Dunaliella had noticeably green guts.

Bipinnaria larva of Dermasterias imbricata. 29 February 2016 © Allison J. Gong
Bipinnaria larva of Dermasterias imbricata, fed on Dunaliella tertiolecta, age 7 days.
29 February 2016
© Allison J. Gong
Bipinnaria larva of Dermasterias imbricata, fed on a mixture of D. tertiolecta and I. galbana. 29 February 2016 © Allison J. Gong
Bipinnaria larva of Dermasterias imbricata, fed on a mixture of Dunaliella tertiolecta and Isochrysis galbana, age 7 days.
29 February 2016
© Allison J. Gong
Bipinnaria larva of Dermasterias imbricata, fed on I. galbana. 29 February 2016 © Allison J. Gong
Bipinnaria larva of Dermasterias imbricata, fed on Isochrysis galbana, age 7 days.
29 February 2016
© Allison J. Gong

Fast forward two weeks, and the larvae were 20 days old. By this time they had progressed from the bipinnaria stage to the brachiolaria stage. The interesting thing was the absence of green pigment in any of the guts, even those that were eating only green food. The D. tertiolecta larvae looked good, actually. They were a little smaller than the other larvae but were perfectly formed.

Brachiolaria larva of Dermasterias imbricata, fed D. tertiolecta, age 20 days. 14 March 2016 © Allison J. Gong
Brachiolaria larva of Dermasterias imbricata, fed D. tertiolecta, age 20 days.
14 March 2016
© Allison J. Gong
Brachiolaria larva of Dermasterias imbricata, fed D. tertiolecta and I. galbana, age 20 days. 14 March 2016 © Allison J. Gong
Brachiolaria larva of Dermasterias imbricata, fed D. tertiolecta and I. galbana, age 20 days.
14 March 2016
© Allison J. Gong
Brachiolaria larvae of Dermasterias imbricata, fed I. galbana, age 20 days. 14 March 2016 © Allison J. Gong
Brachiolaria larvae of Dermasterias imbricata, fed I. galbana, age 20 days.
14 March 2016
© Allison J. Gong

Obviously all of the larvae are assimilating enough of their food to grow and develop normally. I looked at them today but didn’t have time to take pictures. Qualitatively there is no difference between the Dun larvae and the Dun/Iso larvae. In the Iso jars, however, there are many larvae at earlier stages; some are still at the “jellybean” stage. I don’t know if this is because these larvae are developing more slowly, or because of some nonrandom distribution of earlier stages into those jars when I was setting up the feeding treatments.

Next week I’ll measure the larvae again, and will have three data points to track growth trajectories.