Tiny Starfish hermaphrodites with live cannibal babies!

Image by Nuytsia@Tas

Data for this post was derived from Maria Byrne's 1996 paper in Marine Biology: "Viviparity and intragonadal cannibalism in the diminutive sea stars Patiriella vivipara and P. parvivipara (family Asterinidae) vol. 125: 551-567 which is a pretty neat piece of work that set the groundwork for their paper in Biology Letters which was just published today! Today's post has been reported in the news (here) .

Our story begins with an overview of two unusual and quite tiny starfish! Some details:

• Occur in Tasmania (Southern Australia) 
• Two species, Parvulastra vivipara and P. parvivipara occur on rocks and surrounding areas.
• One of those starfish, P. parvivipara is among the world's smallest adult sea stars. 

Indeed! Look how cute and tiny they are!

Image by Nuytsia@Tas

But the  truth is that these tiny little starfish have all kinds of shocking sex secrets!

1. Both Species of Parvulastra are self-fertilizing hermaphrodites. 
I have written about similar species in the same genus (Parvulastra) here. 
Yes, that's pretty much self explanatory. Individuals are simultaneously both male and female AND if need be they can fertilize themselves. 

They typically have between 6 to 8 female gonads and 1 predominantly male gonad. However the amount of sperm present would not be expected in those species which are exclusively self-fertilizers-so SOME outcrossing (ie sex with other individuals) does occur.

Image by Nuytsia@Tas

2. Parvulastra broods juvenile starfish in a brood chamber (aka "live birth" aka viviparity)
Several species of starfish are known to possess "brooding" behavior (I've written about them here). That, is the adult "carries" either internally or externally several tiny juvenile starfish with it until they are ready to move off on their own as full adults.

Each adult Parvulastra carried multiple juveniles across a range of sizes. Here was one example of a clutch containing 30 individuals from ONE large individual. Number varies with size..

scale bar= 1.0 mm, From Byrne 1996, Fig. 4e

These further images from Byrne's paper give you an idea of where they are located. Essentially throughout the body cavity between gonads. This differs from other species which can have them living around the mouth or in other locations.

From Byrne 1996, Fig. 4a

So, eventually, those little baby starfishes have to leave the comfort of the mother's body cavity. This happens when they reach about 25-30% of the parent's body diameter.

The downside of having brooded juveniles is that they tend not to go very far from the adult. In other species, the larvae would be dispersed over wide distances but here, they are retained or crawl away, staying near the parent.. 

Eventually, they exit via openings in the abactinal body wall called GONOPORES. 

But what motivates the exit? 

3. Those juvenile starfish are cannibals! (aka intragonadal cannibalism)

Life is harsh and these starfish know it better than anyone. The gonads in these animals are pretty small which implies that food for the juveniles isn't really enough to keep them sustained on their own..

So, as soon as the brooded juveniles develop a mouth they begin feeding on their siblings in the body cavity! In the specimens examined several of the larger brood individuals, which contained traces of the smaller ones in their gut contents in addition to other observations..

Several possible reasons may motivate the departure of the smaller juveniles from the brood space. Temperature or any number of factors.

Byrne speculated on one reason that juveniles may vacate in order to avoid being fed upon by their larger siblings.. Here is a cartoon supplied by the Echinoblog Art Dept. which illustrates this notion (which to be honest was mentioned as only one sentence by Byrne in her paper).

Thus starfish join the illustrious ranks of those animals which have active, intrachamber type young which feed on one another including sharks, fishes and salamanders and insects-although there's a bunch more..

4. Exit to the Outside World! 

Ultimately, then we see various brooded juveniles vacating the brood space via the gonopores (which flex and open) with the tiny juveniles emerging on the surface and eventually moving away...

Fr. Byrne 1996, Fig. 8b

Thanks to the intragonadal cannibalism however, sometimes you get a REALLY big one which continues to grow INSIDE the parent.  Ultimately reaching a size at which it cannot physically escape on its own..  

Yikes! Talk about living in your parent's basement! 

From Byrne 1996, Fig. 4h

5. Reproductive Impact on Populations

As indicated above, a recent paper by Carson Keever and others has found some significant drawbacks that this unusual reproductive behavior will have on populations of Parvulastra.

• Self-fertilization by hermaphroditic adults and brooding behavior causes strong inbreeding and "genetic poverty"
• There was nearly a complete loss of genetic diversity among all populations of Parvulastra and given the very restricted geographic range of these species+ the very limited way they can disperse their juveniles across wide distances there's little potential for populations to expand.
• Thus, these live-brooding species with little to no gene flow display a high risk of extinction

So, there is serious concern about these species to withstand any kind of temperature or climate shift. The populations of these live-bearing starfish species is pretty small and pretty restricted. Potentially any kind of abrupt habitat change could wipe out these starfish with these unusual life modes..

Starfish with Babies! Brooding Behavior & Pseudocopulation Revealed!

Today: BROODING Juveniles!  Wait, What?  No, NOT like this

Seriously! This is one of the top images that comes up in a Google search for "brooding"

I meant Brooding juveniles like THIS!

from the Smithsonian NMNH USARP

In other words, these are "baby" starfish that are cared for by the mother until they are ready to head off ont their own. Parental investment resulting in a succesful offspring. 

Sometimes starfish (and indeed most echinoderms) can appear kind of alien. No head. Mouth on the bottom. 5 part radial symmetry. Strange adaptations. All kind of weird sometimes.

So, I suppose its appropriate that the WEIRDEST of ALL echinoderm (and starfish) behavior is that starfish have this almost mammal-like (or at least, vertebrate like) behavior!!   Some starfish species will actually brood and carry little starfish just like the cutest little furry thing you can think of!

Now, most starfish have a fairly straightforward reproductive cycle.

Eggs and sperm are ejected from the males and females-they fertilize and go on to form larvae which swim in the water developing through different stages, eventually eventually settling down onto the bottoms and growing up to become proper "adult" starfish.

But many starfish species stray from that typical cycle, and somewhere between the time the sperm fertilize the eggs and the settled "babies" are established the whole life cycle CHANGES to give you this:

Yes. Tiny baby or small juvenile starfish which are held by the mother around the mouth! (this varies as we'll see). Why do some starfish do this?  And not the more 'typical' behavior?

Scientists have known about brooding behavior in several species of starfish since the 19th Century but only recently has there been the extensive observation and insight to finally piece together the complete story!

The Story of Leptasterias polaris
Information herein is based on a paper by Jean-Francois Hamel and Annie Mercier at Memorial University in Newfoundland. which you can find (here) in Biological Bulletin from 1995 (vol. 188: 32-45)

They studied the large, Arctic/subArctic 6-rayed starfish Leptasterias polaris which occurs in the North Atlantic, Arctic and North Pacific Oceans.

Image by Claude Nozeres  from the Canadian Registry of Marine Species

Hamel and Mercier's paper exhaustively studies L. polaris' complete reproductive cycle, which pretty thoroughly documents the reproductive behavior in this species.  Bear in mind, that this starfish has been known since 1842 and yet our knowledge of its reproduction has only come to us recently (published in 1995)!

Information on brooding remains of interest-but the behavior and its evolution is poorly understood.

1. PSEUDOCOPULATION

Figure 1 from Hamel & Mercier 1995

 As a prelude to the actual spawning there are massive aggregations of these animals. They're involved in an unusual behavior known as pseudocopulation. There's no penetration or combination of sexual organs, nor is there any actual spawning. The animals all just get together into a big pile. Sort of preparation for the main event.

Bear in mind, OTHER than during mating season (November to February), these animals all typically ignore or even avoid one another.

Many echinoderm species practice pseudocopulation which I've written about here. Its not always clear why different species pseudocopulate. But one thing seems clear: It helps the chances of their sperm and eggs get together.

2. Spawning! There were no pics of actual Leptasterias spawning, so here instead is a closely related Asterias. I have discussed this spawning on armtips position here. It is observed widely across cold water and tropical species.

Image by Tom Ashton

Spawning in Leptasterias polaris males begins as the water gets cold, about 2 degrees C. 

Sperm (male cells) are negatively buoyant, or in other words, they sink to the bottom and form sort of a film. The sperm then go dormant until they come into contact with the female's eggs..

3. The Female Pinwheel formation. Stimulated by the males, and following the deposition of sperm on the bottoms, the females proceed to eject the eggs onto the sperm so that fertilization can proceed.

The deposition of the eggs onto the sperm re-activates the sperm allowing them to combine and fertilize.

During this phase, the females adopt this "pinwheel" formation

From Mercier's L. polaris site

Here (from Figure 5 in Mercier & Hamel) we see a close up of eggs UNDER the female in C. Which then grow up into the cute as the dickens starfish in D.  Growth was after about 5 and half months.

4. After fertilization, development proceeds. Here's a summary panel of the different stages. The top row is the developing embryo. It continues through different stages until it reaches "J." 

At that point the animal is practically ready to move off on its own..

Figure 9 showing development from embryos to small starfish 

Interestingly, Hamel & Mercer found that the development proceeded on its own if the embryos were unbrooded.  They suggest that brooding is behavior which protects the embryos/juvenile starfish from debris and other materials. Animals observed in the field were clear of excess materials.

Protection was also a likely consideration since unprotected embryos/juvenile starfish were rapidly devoured by sea urchins or other grazing animals if they were not protected by the adult. 

 The whole cycle is sumarized in this convenient cartoon!

Figure 4 from Hamel & Mercier 1995

There were MANY more details! If the topic of brooding interests you I urge you to check it out!

BUT That's NOT the end of it!  

5. Brooding is diverse.  SEVERAL different species of sea stars brood. Almost all of them are either cold-water species, living in the deep-sea or at the poles. Sometimes brooding is in temperate water species.. But typically not in the tropics.

Brooding also takes different forms. The oral 'mouth' or gastric brooding mode is but one kind. Here is Diplasterias from the Antarctic!  MANY starfish in the Antarctic brood juvenile starfish!

from the Smithsonian NMNH USARP

For example, in the suspension feeding brisingids, the Antarctic species Odinella nutrix, broods babies  in special chambers made from the arm spines present between each of the arms.

There is the strange Japanese/Russian/North Paciic Trophodiscus (go here to see more) Juveniles are brooding on the TOP of the animal among the spines (called paxillae) that compose the surface of the disk.

Here is a living specimen. Image by colleague Yoichi Kogure!

Close up

And then there's Tosia neossia, recently discovered in Australia. This species broods but without actually keeping the babies physically on the body. They are kept spread out near the animal... See the orange dots in the picture below?  That's the juveniles...  I wrote about this species here.

Here's the tiny Tosia crawling larvae!

And in the deep-sea, there is the weird "sea daisy" Xyloplax!

And that's not to mention brooding in sea urchins, ophiuroids, crinoids and sea cucumbers! and MANY other invertebrates!  Starfish brooding is just the tip of the iceberg!

The Hidden Treasure of Trophodiscus!

Today, we take another look at some of the exploration and discovery that goes on Behind-The Scenes in the museum I work in.

I previously blogged about this subject. The short version: a huge collection of starfish returned to us with great historical value but which had been hidden away in storage for some 30+ years.
Some interesting stuff...but also, some TREASURE.

MANY scores of specimens among MANY boxes:
So, the SUMMER has finally arrived! And with the summer?

INTERNS & STUDENTS (courtesy of the US Antarctic Research Program)! Bless their little hearts!

They got right to work on unpacking, curating and cataloging the big-boxes-o-starfishes & such!
When you go through a 30+ year old collection like this, you find many...unusual items (but also TREASURE!-as we'll see!).

So, what have we got?

1. Funky Antique biscuit boxes!
2. Unfilled University of Wellington Zoology Program Application!
...but best of all...THIS weird little starfish: Behold: TROPHODISCUS!!!!
Trophodiscus (Family Astropectinidae) does something pretty cool-it BROODS babies.

Now, lots of starfish brood (like this one) but THIS species does so, in a unique way.

On the top surface of these animals are structures known as paxillae. Tall columns that are covered by spines. These are common to the order Paxillosida, which a group of sea stars that live in unconsolidated sediments-mud and sand.

The paxillae are thought to act as kind of a tent. The gills (papulae) are found at the bases of each paxillae and not only protect the papulae from being clogged-but there's fine cilia that cover the surface that push microcurrents so they can respire!
Trophodiscus keeps those small starfish babies on the body surface among the paxillae!!

Look at the little star-shaped babies (in the red circle) living between the arms:
and close up....
Where do these funky things live? A review of this species was recently performed by my colleague Yoichi Kogure . See this paper here.

Kogure even gave it a Japanese name: Komochi-momiji !! (I will have to find out what that means!)

They occur in the Sea of Okhotsk and the Japan Sea in relatively deep water in 150-300 m and that's all. They're pretty rarely encountered.

So, when we pulled one out of a box that had been in storage for 30+ years??

Yow.

Buried treasure, baby.

Fun Leptasterias Facts!

What? So, you wanna know more about Leptasterias?

ha! Well, ask an ye shall receive!!!

These are a follow up to the last post and are taken from various papers by Bingham et al. (2004), Foltz et al. (2008) and Pearse & Beauchamp (1986). The best known Leptasterias spp. are the Leptasterias "hexactis" forms from the west coast of North America and Leptasterias polaris in the Arctic/North Atlantic..

(image from Ibarra & Bingham's L. hexactis page)

Leptasterias broods! From the big Arctic L. polaris to the tiny subArctic L. "hexactis" forms...

• The California forms brood from Jan-Feb-March-April and take 6-8 weeks to develop.
• Larger adults produce larger embryos- a doubling of arm radius in brooding females resulted in a 3 to 4 fold increase in egg production.
• Larger females produce more eggs but have a harder time carrying them completely through the brooding season.
• If "quality" and success is related to overall egg volume, then its possible that egg volume an size is possibly a predictor of survival to the juveniles.

Leptasterias brooding posture varies....
The Leptasterias "hexactis" posture......

(from Chia, 1966)

The Leptasterias polaris posture....

(from this website..)

What does Leptasterias eat? Mostly mollusks, barnacles and such...
How long has Leptasterias been around?
Based on some recent work by Dave Foltz and colleagues (including myself) we used several gene markers to estimate how recently the various sister species of Leptasterias diverged!

So, all basically, all of the 'species complex' stuff I wrote about earlier? When did that happen?

That usually suggests a relatively recent speciation time frame. They diversified/speciated/or whatever you want to call it, ONLY about 0.5 to 1.2 Millions of Years Ago (Mya)!

Geologically, that's quite young..but put this into context for people reading this? This starfish likely speciated in the Pleistocene. What else happened in the Pleistocene?

There were glaciers. A LOT of them. Some 30% of Earth was covered by ice.

• Image by Jeff Huffman

What else was alive in the Pleistocene? (Images from Wikipedia)

This little, tiny starfish?? is prolly kinda sorta AS OLD or OLDER THEN HUMANITY (and its pretty young for a starfish!)
....and THAT is the rest of the story!