Monday, February 27, 2012

Bacteria in the Belly of the Beast! Prokaryote Diversity in Abyssal Sea Cucumbers!

(photo from the USNM Invertebrate Zoology Collection)
This week a follow up to an earlier blog I wrote in October last year about microbes in the guts of deep-sea holothurians!

This new paper is by Teresa Amaro, University of Aveiro in Portugal and her colleagues and has been recently published in Deep-Sea Research I vol. 63: 82-90. (she also wrote the earlier paper that I wrote about above)

This paper focuses on this lovely echinoderm champion-the sea cucumber Molpadia musculus-which occurs throughout the North Atlantic, buried in deep-sea (circa 2000-5000 m depths) mud.
(photo from the USNM Invertebrate Zoology Collection)
Molpadia are infaunal deposit feeders-that is they live buried in the mud, head down with mouth directed into the soft, muddy goo... (the mouth is shown below-this is the part that faces into the mud! Lovely, yah?
(photo from the USNM Invertebrate Zoology Collection)

Their "tails" presumably face upward to permit the feces to vent out on the surface, following ingestion of the mud/sediment...
(photo from the USNM Invertebrate Zoology Collection)

Molpadia can occur in very high biomass and in great abundance on the deep-sea floor with some 220 individuals per square meter!!

Bacteria and Archaea on the Deep Benthic Floor!
So, you've got a big, living dirt-eating vacuum cleaner buried in the mud of the deep-sea floor. What are they doing down there?? What are they interacting with? Are they Eating?
(photo from the USNM Invertebrate Zoology Collection)

For years, it had been noticed that there is actually quite a lot of microbial life present in the oceans. Scientists have been using methods known as DNA fingerprinting to recognize the amount of life that is present on deep-sea bottoms.

The diversity we focus on here, emphasizes two of the major Kingdoms in the overall Tree of Life-The Archaea and the "Bacteria" or the Prokaryotes-those with less developed cells relative to the eurkaryotes. Note in the diagram below.. "Eurkaryota" refers to organisms with full and complete cells, such as algae, protists and all the animals.
(Image from Wikipedia)

The prior blog that I wrote about this showed that there different "kinds" of microbial life present not only on the sea bottom but actually IN the guts of these deep-sea sea cucumbers.

Amaro's newer paper now shows that there is an astonishing diversity of microbes associated with the gut contents in Molpadia musculus! And details the distribution and diversity of the kinds of microbes present.

Amaro and her colleagues surveyed the abundance of different prokaryotes both in the sediment (measured from sediment cores) and at different points along the gut of Molpadia and found this....
(Fig. 2 from Amaro et al., 2012)
First (top-Fig. 2a) , that the actual amount of prokaryotes (this includes both bacteria and archaea) was highest in the top 1 cm of sediment.

Second (bottom-2b) That after survey the abundance along the animal from the gut to the end, the greatest amount of prokaryotes was actually found in the oesophagus (i.e., the front end of the intestine) of the animal.

The latter result likely shows the result of digestion with most of the food (i.e. bacteria) being digested as it proceeds to the midgut and so on...

Both of these results make sense. Prokaryotes are settled out on the surface and the oesophagus (the front end of the intestine) is where all of that enters into digestion.

What kinds of bacterial diversity did they find?
The authors counted the diversity of bacteria in terms of Operational Taxonomic Units (OTU)s-that is a general term that refers to the different types of organisms or species present.

They found 28 to 71 OTUs in the surrounding sediments
but about 33 to 105 in the sea cucumber itself!
(Fig. 4 from Amaro et al, 2012)

The authors further compared the abundance and composition of the bacterial OTUs (i.e., the diversity) between the sea cucumber and the surrounding sediment.

Now, if the surrounding bacterial were food-one would expect the same diversity in the sea cucumber as in the nearby sediment.

BUT, as it turns out, about 40% of the bacterial OTUs were uniquely associated with the gut contents and were ABSENT from the surrounding sediments!

Some Further Dynamics from the paper...

1. Prokaryotes decrease in abundance along the gut. From the above Figure 2 we see the abrupt decrease of abundance of prokaryotes from the oesophagus to the hind parts. This was a 6-fold reduction from the oesophagus to the hind gut.

This suggests that GREATER than 80% of the total were digested by the animals.

2. Archaea vs. Bacteria in the Hindgut. They also found that among the prokaryotes-bacteria accounted for only about 55% of the total number found in the oesophagus but only 35% in the hindgut, BUT archaeans actually increased in the hindgut! Why? The authors suggest that the different kinds of prokaryotes are used differently across the intestine..

3. But do the prokaryotes keep Molpadia fed? Well, in a word: No.

It turns out that these bugs only contribute about 0.5% of the total organic carbon used by individuals in the study. The authors conclude that Molpadia, at least, does not rely in any significant way, on prokaryotes for their food requirements.

4. So, if not food-then what are they for?? As indicated above- the DNA fingerprinting identified the fact that the "bugs" in the surrounding sediment were significantly different from those in the sea cucumber itself.

So the authors conclude that the animal carries the prokaryotes around in its gut as commensals-possibly to facilitate digestion in a manner similar to how termites and some mammals (such as ourselves) carry around a prokaryote fauna to facilitate digestion. (think of it as yogurt for sea cucumbers!)

And so there we have it. Some deep-sea sea cucumbers are just big bags filled with prokaryotes that feed on mud and ooze!

Tuesday, February 21, 2012

What can the Internet do for Biodiversity? Let's study COMMENSALS!! Some biology can't be studied from samples!

Hostess with the Mostest
(photo by MerMate)
The Internet is amazing!

But often one gets the impression that a lot of people haven't quite realized the potential for discovery.
What can something as simple as humble as a photostream or video channel do for science?

Especially for something like exploring biodiversity? For looking at the many different kinds of animals -some that have yet to be discovered?

What makes the Internet so potentially important is YOU. Everyone out there. A nearly infinite amount of eyes, cameras, videos, talent, and interest.

What does that mean? That means that some people have the good (nay excellent!) graces to take pictures (and/or videos) of moments and/or species in places that many scientists just aren't or can't be. I believe the buzzword is "crowd sourcing".

Sources like Flickr and YouTube thus become great treasure troves of potential discoveries.  Moments and relationships caught of the live animals doing their thing!

So, today I thought I would use some videos and images to demonstrate some commensal relationships between sea stars/starfish) that most people don't often see because they are best seen in the wild when the animals are left to their own devices.

........But then, some incredible individual took a picture or video of it!

And in conjunction with a little bit of narrative (on my part) there is another layer of appreciation of these images as more than just aesthetically pleasing-but a representation of something in nature that everyone can enjoy. GO!

1. Fish Living commensally among the oreasterid Protoreaster nodosus

This video was exciting! I'd never heard of fish living in and around asteroids and have yet to discover prior accounts.

Was this unique or does it happen all the time? Are fish juveniles tied to sea stars? Is this important to their life cycle?

Note also the tiny little brittle stars living on the spines! Probably Ophiactis savignyi-a species of ophiuroid that may literally live everywhere!
Cool star 2 (photo by Mermate)

2. The benthic ctenophore Coeloplana living on the surface of Echinaster luzonicus
Benthic ctenophores on Echniaster  luzonicus (Coeloplana astericola)
(photo by Arne Kuilman)

So, what are these?

Ctenophores are usually found swimming in the water column like this (intro to the group in the video)

But some of the really WEIRD ones live on tropical bottoms and look like this.. (note the feeding tentacles emerging out of the two top "lobes")

But some of these benthic ctenophores are these worm-like forms and they actually live ON sea stars, such as this Echinaster luzonicusBenthic combjelly on Luzon seastar  (Coeloplana astericola)
(photo by Arne Kuilman via Flickr)
I don't know if they are necessarily rare..but people don't see them often. They can be difficult to see and who thinks to look for what is basically a bottom-living jellyfish??

On top of all this- the benthic ctenophores themselves almost never preserve well. So scientists have relativelly little data on them. When I learned about these in Invertebrate Zoology way back when, there was only a footnote about these critters.

If we were lucky-we MIGHT see one in our lifetime. Now-everyone can!
Parasitic flatworms Hostess with the Mostest
(photo by "MerMate" on Flickr)
Here's one close up..

Sea Star (Starfish) Rider
(photo by Mark Atwell via Flickr)

3. This looks like a polychaete and/or a flatworm living on another specimen of what looks like Echinaster luzonicus (Taiwan? or the Philippines?)
(photo by Star Tsai via Flickr)

4. And finally,the shrimp Periclimenes that lives in and around various big tropical sea stars.

They're all called P. soror in the pictures but there seem to be so many-I'm not entirely sure its the same species.. But here's a bunch...

This one living on the ophidiasterid Linckia laevigata in Komodo, IndonesiaSoror Shrimp on Blue Starfish (photo by Fiona Ayerst)
this one on the Crown of Thorns-Acanthaster planci..4113 Commensal shrimp on crown-of- thorns

(photo by Diver Ken)
Periclimenes soror on Acanthaster ellisii
(photo by Olin Feuerbacher)
This one looks like a shrimp living in/around the uncommon oreasterid Halityle regularis
Pin Cushion Star and Periclemenes Shrimp
(photo by Shaun-in-Munich)
On/around the mouth of a "cushion star" so..Culcita?Shrimp On Cushion
(photo by pummkin)
In and around Echinaster luzonicus (oreasterids aren't the only ones with shrimp!)Who's the star?

(photo by MerMate)

If you had collected any of these shrimp without the asteroid (or vice versa) it would have been difficult to make the animal-animal association. What function do the shrimp serve? What do they get out of it? Protection?

These images may seem just like holiday snaps-but to some scientist-they may demonstrate some new species/behavior/relationship!

So, if you're in some exotic part of the world and have some weird, neat picture that you've never seen before let a biologist who knows a thing or two-take a look! You never do know...

And uh... for those with more...mercantile motivation, scientists don't do it for the money (and mostly don't have a lot to give away).

Monday, February 13, 2012

Valentine's Day-Feb. 14th The Echinoblog Twitter Feed gets SEXY!

So tomorrow as an Echinoblog EVENT! I will be Tweeting as MANY Weird marine invertebrate (and some vertebrate) SEX videos as I can! Sea stars! Nudibranchs! Slugs! Worms! Hermaphrodites! Pseudocopulation! Penis Fencing! Giant Sperm! Yow!

Check out the new Echinoblog Twitter Updates in the side column
Enjoy these pics of the tropical Archaster typicus caught in the act of PSEUDOCOPULATION!! More on that tomorrow..
Common sea star (Archaster typicus)

Common sea star (Archaster typicus)

Sunday, February 12, 2012

2012 Scientific MEETING Announcements!

If you're a student or researcher and want to meet your other Echinoderm colleagues/fellow echinoderm otaku then the 14th International Echinoderm Conference is for you!!

Held in Brussels, Belgium, August 20-22, 2012 near one of the most active echinoderm research centers in the world! Click here or on the image below to check out details for registration and etc.

Coincidentally, an announcement was also made for the 13th Deep-Sea Biology Symposium held December 3 to 7 in Wellington New Zealand!

Click here or on the graphic to check out registration and other details!

Tuesday, February 7, 2012

Sea Cucumber Defense Pt.2! Evisceration of Cuvierian Tubules!

Sea Cucumber defence 2
Image from Adam Broadbent on Flickr

Last week I wrote up a general overview of evisceration (and regeneration).

Evisceration is a general term that describes the expulsion of how SOME sea cucumber's "viscera"-intestines, respiratory structures, gonads, etc. (varies with time of year and presumably the species) is EXPELLED through the body wall. Here's a nice video that shows what that looks like..

In many cases-this is interpreted as a defense-but as you read last week, there is some evidence that evisceration can also serve to aid in excretion of waste and to aid in other bodily functions. Some have hypothesized that evisceration serves to expel parasites, such as these lovely pearlfish! That live in the cloacas of sea cucumbers! (Read more on that here and re-live the glory of anal teeth!)

But if we get away from the general phenomena of evisceration-we can focus on the defensive ecology!! Specifically in tropical sea cucumbers in the Aspidochirotida (and I believe only in the Holothuriidae) which have special organs ONLY for eviscerating!

Enter: What are Cuvierian Tubules!
These organs are known as Cuvierian Tubules! Cuvierian Tubules (named for their discoverer-the French zoologist Georges Cuvier)

Cuvierian tubules are branching structures that occur on the respiratory tree (seen above in blue) of sea cucumbers.

They branch off the respiratory tree and are expelled through the body wall at oncoming predators, such as fish, crabs, or predatory echinoderms, such as sea stars. But how effective are they? How do they work? How do these affect the sea cucumber's day to day ecology?

Ecology and Defense
Much of the information used in this section is taken from an excellent paper by Jean-Francois Hamel and Annie Mercier in Marine & Freshwater Behaviour & Physiology 33: 115-139 and this: physiology and regeneration oriented papers by Didier Vandenspiegel, Michel Jangoux and Patrick Flammang in Biological Bulletin (2000). and this: Patrick Flammang, Jerome Ribesse and Michel Jangoux in Integrative and Comparative Biology 42: 1107-1115.
Hamel and Mercier studied the efficiency of Cuvierian tubules in 3 species of tropical sea cucumbers (note that idents were taken on face value from labels-but used for educational purposes)

Bohadschia argus
Sea Cucumber - Bohadschia argus - PC092244
Holothuria leucospilota
Long black sea cucumber (Holothuria leucospilota)
and Holothuria marmorata (also called Bohadschia marmorata)
Bohadschia marmorata

Some ecological dynamics...

  • Cuvierian tubules are "shot" from near the anus and so aim is directed at the threatening stimulus.
  • The oral tentacles or mouth seems to be most sensitive to being threatened. Whenever the mouth was stimulated (i.e., threatened) the animal would retract the tentacles and arch the body to orient the anus towards the "stimulated" area. Water was taken in through the anus followed by expulsion of the Cuvierian tubules with expelled water.
  • Interestingly-the slowest reaction by the animal ended to be if it was stimulated or provoked around the anal region. Maybe the rear regenerated more readily??
  • Cuverian tubule "stickyness" was most effective on slower moving predators such as crabs, snails and sea stars (87-100% targeting success). This was generally not as effective against fish (5-35% targeting success)
  • (Fig. 1 from Flammang et al)
  • Lab trials showed that if a potential predator was touched by Cuvierian tubules-about 96% of those predators avoided the sea cucumber for about 3 days.
  • If the sea cucumber LACKED Cuvierian tubules then those individuals were devoured or bitten to death at a higher rate.
  • Tubules that did not ultimately stick to a a surface can be quickly pulled back in or retracted.
  • Even if Cuvierian tubules have been completely exhausted, the other viscera can STILL be used as a defense.
  • Regeneration of Cuvierian Tubules took 15 to 18 days (so about 2 weeks-with complete regeneration in up to 5 weeks)
Flammang and his associates found that tubule "tenacity" or the adhesive strength varied with the surface it was in contact with, temperature and salinity of sea water and the time following expulsion from the body.
Sea Cucumber defence 2
Image from Adam Broadbent on Flickr

Regeneration of Cuvierian Tubules

There's a whole blog that is to be written about all of the various dynamics involved in sea cucumber regeneration.

But what it comes down to is that there are many cells which are "undifferentiated" that is-their use in tissue has not yet been determined by the body's needs.

These "proliferate" or become more numerous and as regeneration begins, these undifferentiated cells decreases and the "specialization" or "differentiation" of cells begins to replace the lost tissues (i.e., the Cuverian Tubules).

Vandenspiegel, Jangoux and Flammang summarized the strategy for Cuverian Tubule defense and regeneration very eloquently and so I repeat it here:
Holothuroid Cuvierian tubules thus constitute a very efficient defensive mechanism. Indeed, in addition to their remarkable structural organization, which accounts for their adhesive and mechanical properties, their large number, sparing use, and particular regeneration dynamics also make them an almost inexhaustible line of defense maintained at limited energy cost.

Thursday, February 2, 2012

Helping my friends at the Field Museum: Crown of Thorns Starfish Outbreaks-not so simple..

So, I had recent cause to have seen this very nice video about the Crown-of-Thorns video (Acanthaster planci). Which touches on some neat anthropological facts..

'Na Bula': Fiji's Crown of Thorns from The Field Museum on Vimeo.

But if I could comment on the reasons for the crown-of-thorns outbreaks?

There are not any published theories that claim that this animal's regenerative abilities was the cause of the huge population outbreak that this species is known for throughout the Indo-Pacific.

Outbreaks are huge "plague-level" spikes of the population of this species. Here's a nice short video that addresses the topic in general

Its a complicated phenomena, and a single reason may not be the cause, but one of the most recent papers by Jon Brodie suggests nutrient enrichment of larval settlement is a likely explanation.. Here is a blog I wrote for Ocean Portal about it.

Historically, several reasons have been offered and the idea regarding nutrient enrichment is the most recent-but NONE have ever speculated that regeneration was a cause.

But don't take my word for it..

I hope that my colleagues in Chicago take this in the best possible way. I love hearing about the cultural side of the animals I study and I stand happy to hear about future reports on their work!