Friday, February 22, 2013

Extra! Solaster feeding caught forever in the museum!

A cool find that a student (Eric T.) fr. American U. found while working on a project.. Solaster endeca with the arm from what looks like Asterias rubens
 Here is the predator alive...
Solaster endeca
and the prey (where the arm comes from)
Asterias forbesi, dorsal

Solaster is one of the few starfish which is known to feed primarily (at least in some species) on OTHER starfish!  Here was something I wrote awhile back on the Pacific Solaster dawsoni...

morning sun star- solaster dawsoni
and here is a nice pic of the North Pacific S. dawsoni feeding on Hippasteria
It is so fearsome that EVEN the sunflower star Pycnopodia RUNS from it!

and here's a nice bit about when starfish are eating and uh... overreach...


Wednesday, February 20, 2013

The Anus as a Second Mouth! A Sea Cucumber that feeds via its butt!

The Beast
Image by Ken-Ichi
This year it will be FIVE years since I began the Echinoblog in 2008. I always used to worry about having new topics to write about-but I'm quite happy to say that I've yet to run out of fantastic images or new discoveries to be shared.

Today is a good case in point. A GREAT new story from the journal Invertebrate Biology (go here) by two of my favorite colleagues, Will Jaeckle at the Illinois Wesleyan University and Richard Strathmann at Friday Harbor Laboratories in Washington.. a NEW paper that MUST be shared!
This week, Echinoblog brings you:
A sea cucumber that feeds not just using its mouth but ALSO via its butt!!

First, Let's look at some basics...
Jaeckle and Strathmann were studying the Pacific Northwest species Parastichopus californicus-the handsome fellow pictured above (and below)!  These occur along the west coast of North America in relatively shallow water...
Cucumber1_6377 copy1a
Image by Bill Pennell
Here is the primary way that sea cucumbers feed-by using the feeding tentacles surrounding their mouth to ingest tiny food particles or sediment.. as such..
As it turns out, sea cucumbers (and many other invertebrates) use their anus as an opening for pumping water in and out of their bodies!
Image by bswift
This whole water pumping into and out of the mouth/anus thing is actually pretty common- a bunch of worms, crustaceans and other echinoderms perform this same thing.

As a generaltiy-sea cucumbers can pump quite a bit of water in and out through their anus-with tropical species measured between 40 to 860 milliliters/hour..that translates to about 3.6 to 4 cups of water per hour! 

Sea cucumbers are essentially a big fleshy tube with a mouth and a butt that pumps water through itself!  Here's the basic anatomy below...
Note those two bluish/white, feathery branches that come off the cloaca and the anus... those are called the respiratory trees.  That is where water enters via the anus and is used to respire or "breathe". The cloaca has muscles that PUMP the water in! 

So, shocking sea cucumber secret # 1!! Sea cucumbers "breathe" through their anus! 

Here's an actual pictures of these below from Jaeckle and Strathmann's paper (Fig. 1)
Note that one branch of these structures
Water enters through the anus and is pumped via the cloaca (and the cloacal muscles) into the respiratory trees (=long tubes with lots of branches), where there is gas exchange or "breathing".

Note the structure labelled rete mirabile, which is a network of blood vessels which interaces with the gut. That will be important later on!

There's a LOT of water that flows through these areas, so conceivably, could these be used for ANOTHER purpose?  Such as.... feeding?

Jaeckle and Strathmann set to find out!  They used biological tracers such as the isotope Carbon-14 which they applied to various algae cells and other nutrients that were added to seawater.

Evidence for the Anus as a Second Mouth!
Folllowing the trail of traced algae through the sea cucumber, Jaeckle and Strathmann tracked the isotopes throughout the body and found out where they were most abundant.

Enter The Rete Mirabile! (this sounds like a great episode of Star Trek doesn't it?) Basically after exposing the sea cucumber to tagged algae they found the tags taken in and were present in highest abundance in the Rete Mirabile which connects the respiratory trees with the gut..

This supports the notion that organic food is drawn in from the respiratory trees and eventually transferred to the gut..
Fig. 3 from Jaeckle & Strathmann
They looked at specific tissue cross-section of the inside of the respiratory trees. Lo and behold the blue bits in the picture reveal that they are inside and being absorbed!
On top of everything else, histology of the INSIDE of the respiratory trees shows internal tissues that you might expect to find in a gut: such as microvilli (tiny finger like doodahs that serve to absorb or secrete. We have these in our intestine) as well as certain kinds of cells in the stomach lining that are recognized in other animals for digesting food.

Note above that they also found tiny ciliates (protozoans) swimming around inside living commensally. ANOTHER feature common to spaces where food is digested.
Image by bswift
It had been suggested before that the respiratory trees were used only for respiration/breathing.

But the evidence above suggests but rather something more akin to digestion or UPTAKE of nutrient-like material

In other words:  They use their anus as a SECOND MOUTH!

This phenomena is what the authors term "Bipolar Feeding"

To be sure, its not likely that this means of feeding is as substantial as its primary feeding mode (taking organic materials from sediment or from the bottoms via the mouth) but it does appear to be significant. Also, obtaining food in this way may be an important way to supplement its main feeding mode.

Perhaps the sea cucumber version of an  ap√©ritif with dinner?

How does this fit into the "Big Picture"??
At first glance, all of this sounds more like just weird butt stuff..
But let's remember that this mode of feeding is probably present in a LOT of sea cucumbers, which are ecologically important. Such as this post about tropical sea cucumbers being important to sea grass ecology.   And bear in mind that nutrient cycling is an important consideration these days. A LOT more nutrients go INTO sea cucumbers than perhaps was realized.

Another indicator of how echinoderms might be the ecological "canaries in the coal mine" perhaps?

Information like this may seem like an unusual natural history factoid but conceivably things like this can ultimately be VERY important to the big picture... 

Saturday, February 16, 2013

Saturday Night: WHAT is this thing?

Working late alone in the lab, going through a dish of marine inverts collected from a random sample in the Pacific Ocean and you find...something.

Sometimes someone is around to share it with, sometimes not. What does THAT feel like? This video isn't mine but it gives me the same feeling of discovery.

I just found this and I don't know what it is.  THAT's saying something..


Tuesday, February 12, 2013

Starfish Mystery! 3 Oceans,2 Hemispheres,but ONE species?!

Today a post about a NEW paper currently available as advance ONLINE at Marine Biology (yes, there's a paywall) authored by myself and Dave Foltz my colleague (with help from Scott Fatland) at Louisiana State University, and five multi-nationalcollaborators whose role will become clear.

This project originally began because we were studying a relationship between two near-Arctic sea star species. One in the sub-Arctic North Pacific (called Hippasteria spinosa) which occurs widely in Alaska/the Aleutians Islands, Washington, etc.

Hippasteria is a cold-water animal and is important as a predator of deep-sea corals and cnidarians. Here was a blog about some prior species I've worked on...
Spiny Red Star -  Hippasteria spinosa
Image by Davidtodd via Flickr
and Hippasteria phrygiana which lives in the North Atlantic near the Arctic Ocean around the United Kingdom, Norway, off the coast of Massacusetts in North America etc.
Often times, when you see two very similar looking species in far Northern parts, separated by the Arctic Ocean
You can test the relationships between these species using genetics to determine if they are closely related.  Sometimes you can even determine if they are literally the SAME species perhaps separated by time and the history of the region.  Ice bergs and glaciers perhaps??

As it turns out, we found something intriguing...

The more we sampled these 2 species, the more we realized that scientists had assumed that Hippasteria was present from North Pacific to Arctic to North Atlantic.. it turns out no one had ever collected any from the Arctic!! (i.e., nothing in between!)

And to add more to the mystery, there were taxonomic accounts which indicated that there were accounts of the Atlantic species, H. phrygiana in unusual places..namely.. New Zealand!!

We looked at the distribution of this and related turned out that H. phrygiana or species which closely resembled it were present all over the world!

A two-year effort on the part of myself and Dave Foltz was launched!

We managed to obtain samples of Hippasteria from all colleagues over the world!  Our coverage spanned 3 oceans across 2 hemispheres!
  • the North Pacific-Aleutian Islands/Alaska
  • the South Pacific-Chile, Solomon Islands and New Zealand
  • the Kerguelen Islands in the South Indian Ocean (sub Antarctic), 
  • the North Atlantic, the North Pacific-Aleutian Islands
We gratefully acknowledge all of the the co-authors and other scientists who helped us obtain the data we used in the paper!
What we found was pretty amazing. It turns out that from all the populations of similar looking Hippasteria around the world?

There was only ONE species.

We extracted tissue and DNA from multiple populations and found that the genetic differences among the many populations found around the world were minute.  SO minute that there was really no reason they should be regarded as separate species..

BUT there was structure. Different populations show SOME natural differences relative to other populations.

The following two diagrams show what's called "haplotype networks" for the two genes that we studied. The size of the circle indicates the sample size, whereas the different colors shows the region and the lines show the connectivity between the regions sampled..
Fig. 2 Network for COI haplotypes

We sampled two genes but I've only shown one network so that you get the idea.  Basically, there ARE population differences between the populations in the North vs. South Pacific vs. the ones in the North Atlantic..

One Species Around the World! 

You can think of this in the same way that human beings show differences (also called heterogeneity) between populations but are all basically considered the same species. In population genetics-its often the amount of difference between isolated populations that mounts up to indicating different species.

There's actually a LOT of animals that belong to only one species that are found all over the world (other than humans that is!)

Usually though, its small species (such as the brittle star Ophiactis) (see here) that get carried everywhere or perhaps things that swim like jellyfish...
Moon Jelly - Aurelia aurita

BUT this is still kind of unusual. One species that lives on the sea bottom?? From a group of animals not known to be quick travellers or even particularly well travelled?  This species' spread is probably via the marine larvae which were carried via ocean currents...

Widely distributed species often wreak havok with people who describe species (i.e. taxonomists).

Do differences between populations mean many species? Or do they mean one species occurring widely?

In this case-its ONE species. This also has a pretty huge impact on taxonomy. In the old days, many species were identified as new because they were found in new places, or far away from where prior species were known. A lot of the technology to test these relationships was not yet available...

But now that we know,  ALL those species names that fall within the range of our study will be suppressed (via international rules) by the oldest name-Hippasteria phrygiana.  So, for example, the North Pacific Hippasteria spinosa (described in the 20th Century) will now be called H. phrygiana (described in the 19th Century) because they've been shown to effectively be the same.

Another spin- HOW FAST did they Spread Out? and from where?
Further dynamics!
  • There was apparently NO gene flow across the Arctic and we couldn't find any records of this species currently present in the Arctic. So, in one sense they took the long way around....
  • Modelling studies of the genes showed that the three populations had been diverging with little or no connection  (i.e. gene flow) for the past 50 to 75,000 years (roughly the late Pleistocene when). 
    • That means that this species spread out over the world's oceans QUICKLY (not even a million years!) and not that long ago! That in itself is pretty surprising...
  • Could the distribution of these animals (originally spread via swimming marine larvae) be affected by glacial (i.e. ice) cover?  
  • Although evidence was not concrete-it seems likely that Hippasteria spread out from the Pacific to the Atlantic. 
  • This was not a case of spread from human transport. We know this because one of the genes we looked at had changed too much to have occurred in a human time frame.
So there you have it!  A story about a species of starfish living in THREE Oceans! Evolved wide and Quickly!  Not invasive and not an animal that floats around the world as an adult! 

Tuesday, February 5, 2013

Brittle Stars Have TEETH! What do they use them for?

Brittle stars are everywhere. They are the most speciose of all the living echinoderms with over 2000 species (probably MUCH more than that!).

At this moment in time, for studying brittle stars we live in a privileged time because we have several new workers who have taken to studying the various and weird lives of brittle stars!

One distinctive feature of brittle stars that researchers that study morphology have always known about are the unusual jaws present on the mouth of brittle stars. These jaws vary between individual groups of  brittle stars. Its one of the fundamental ways that brittle star taxonomists tell them apart.
These jaws are superficially similar to the ones we see in other animals in that some of them have "teeth" (called oral papillae) and other features which distinguish them.

But other than their usefulness in telling them apart, what function do these "teeth" serve?

A recent open access paper by Karin Boos, an author at the 7th European Echinoderm Conference held in 2010 (available here) addresses and discusses how the jaws might function relative to the feeding biology of two European brittle star species.

First off, Boos reviewed the feeding modes of two species with fairly distinct jaws and teeth.

One of the studied organisms, Ophiothrix fragilis is covered with many needle-like and bristling spines...
Images below by Hsacdirk
Brittle stars. Ophiothrix fragilis.

In life, they hold their arms up into the water and are almost always observed in this position in order to obtain food from water currents. Ophiothrix is a filter feeder.

They gather up food on their arms, which is then moved to the mouth via tube feet.
Brittle stars. Ophiothrix fragilis.

The other species studied was Ophiura albida which is more of a generalist. A sort of opportunistic feeder. Sometimes scavenging on dead animals but sometimes feeding on other smaller animals.

Each species has a different life mode and presumably the morphology, i.e., the teeth of each species reflects how each individual species lives.
Ophiura albida
Image by Danielguip
A brittle star from a completely different group (ie. family) and with a very different set of choppers! Here is Boos' Figure 1 which shows the two "teeth" types side by side. Ophiothrix on the left vs. Ophiura on the right.
Figure 1 from Boos 2013
1. Predator? Or generalist? type jaw/teeth in Ophiura.
Boos takes some pretty nice profile images (her Figure 2) of the papillae (=the "teeth") that allow her to infer some function.
top of pic is the oral surface, bottom is top or aboral. Fig. 2d-3
Boos argued that these teeth are in fact "predaceous (=predatory) dental equipment". Note how all of the "teeth" (=the papillae) were pointy. These, Boos argues, are used in gripping or spearing captured prey before ingestion.

It doesn't take much to take this consideration seriously. Here is some classic video from Neptune Canada showing what looks like Ophiura sp. fighting it out with another individual over some food.

and don't forget this blog about "brittlestars of death" as we saw Ophiura sarsii attacking mobile prey! (vertebrates even!)

Other related members also have jaws/teeth that sort of look like this. Maybe more of these are more predatory than we thought?

2. Ophiothrix-Sharp teeth! 
Ophiothrix (and related genera of brittle stars) occur widely in temperate AND especially in tropical waters. They can be quite striking and colorful..
Electric brittle-star (Ophiothrix sp), GBR, Australia
Image by Arthur Anker
Blue lined brittle star (Ophiothrix lineocaerulea)
thanks to Wild Singapore!

Feeding in Ophiothrix is nicely shown in this video. Food caught on the spines, is moved by tube feet along the arm to the mouth, where the food ball, called a bolus is devoured.

Ophiothrix and indeed ALL members of the Ophiothricidae are well-known in the taxonomic literature for having these unusually striking types of teeth.
Here's a close up!  Usually with a very comb-like appearance... MANY papillae (ie teeth) on each "jaw"
From imaging these teeth in profile, Boos notes that the "teeth" are arrowhead shaped and pretty sharp but also pretty wide.

Boos states that this combination of "sharp" and "wide" serves to cut up and crush the bolus of food as it enters the mouth. Boos argues that the teeth would also be effective for devouring diatoms and/or grabbing parts of or complete  invertebrates in addition to big chunks of scavenged flesh.

And onwards? 
There are LOTS more brittle stars where that came from...  As I had indicated earlier, the "jaws" and "teeth" have been used heavily to classify and identify brittle stars but none were really good at understanding function...

Boos's efforts are a start. Interpretation of these structures has been surprisingly unseen in the literature. 

This for example, is an ophiacanthid from the Atlantic..
 Has a jaw similar to that of Ophiothrix....kinda.
And this euryalid ophiuroid (aka a serpent star)

Further data from observations of actual feeding and perhaps even closer observations with x-rays and measurements of brittle star biophysics may give us more insight into how brittle stars feed!