Thursday, November 14, 2013

Snail Porno - How Slipper Snails Do IT




As a side project in the lab we have been making snail porn (here for full YouTube video).  Trying to get photos or videos of our snails in the act, doing the deed, getting it on... or as we say in lab, copulating or mating.

The last post described how to tell the sex of slipper snails.  Just like lots of animals males have a penis and females have an opening that receives the penis and the sperm.  But, something we would like to know is how exactly does this transfer happen?

The snails are shy and seeing what's going on is easier said than done.  


You can see the penis from the malCrepidula fornicata extending under the shell of the female he is stacked on.




The common idea that slipper snails have to be stacked one on top of the other to mate is not always true.This small Crepidula onyx is extending his penis across the substrate to the female. 


From observations of snails in cups like these we know that mating can last for hours.  Snails are slow, but what is going on under there for all that time?  Recently Matt Starr, a student in the lab, was lucky enough to get this footage of mating in a pair of snails that had been detached from the substrate.
Here the male is just exploring, prior to copulation.

To most people it probably seems that as long as mating happens and successfully produces offspring it's not really important exactly how.  But the details of copulation can shed light on some important questions in evolutionary biology and behavioral research.  For example:  Can females control who they mate with? Why do females mate more often than necessary to fertilize their eggs?
If they mate with more than one male, can females manipulate whose sperm they use to fertilize their eggs? 

Copulation!

We already knew, from anatomy that sperm is passed to the female in an open groove that runs to the end of the penis.  Unfortunately we can't see the sperm moving in the videos.

But we can see that there is a lot of activity on the part of both the male and female.  We can see is that the long thin papilla at the end of the penis inserts into the female genital papilla.  That's not so surprising, but makes us wonder what happens in the many species that lack both the female genital papilla as well as thin extension of the penis.

So far Crepidula incurva is the only species for which we've obtained video.  We hope to find out how copulation differs across species with different penis morphologies and why mating takes so long.  In some animals the male uses his penis to displace sperm that were deposited by previous males, could this be what's taking so long when Crepidula mate?



Wednesday, August 7, 2013

How to Tell the Sex of a Slipper Snail .... And Why You'd Want to....

Quite a few people who ask about our research are surprised that snails can be males or females. They have probably never thought about invertebrates having genders. Some snails, like garden snails, are simultaneous hermaphrodites --- both males and females at the same time.  What's even more surprising to people is that some snails change sex.  In fact quite a lot of the research in our lab is focused on understanding when and why slipper snails change sex.

To conduct experiments on sex change, we need to know how to tell the difference between males and females, and how to identify individuals that are transitioning.

So, how can you tell the difference between a male and a female?  First of all... Not this way:
Mis-information about snail sex abounds on the internet!


Male snails have a penis
Like many males across the animal kingdom, male snails have a penis.  That is, most snails where reproduction occurs via copulation (as opposed to free spawning).  The penis is on the head - located behind the right tentacle.  In small slipper snails the penis can be as long as the male's body length. Imagine having something that size projecting from your head.

Here's a sketch from a publication from the 1940s by W.R. Coe, one of the first researchers to work on sex change in slipper snails.  In this picture the shell has been removed and you are looking at the dorsal view of the snail, with the guts positioned above the foot.



The sketch is not an exaggeration.  This photo from our lab shows a small male mating with a larger female.



In live snails, if you flip them onto their backs you can easily see the penis behind the tentacle as they move their heads around.  The penis is not retractable but they often curl it back behind the head, pointed into the mantle cavity. Flipping the snails onto their backs works well to tell the sex of other marine caenogastropod snails as well.  

Here's what it looks like in Crepidula incurva.



The blue arrow points to the penis.  You can see the eye spot at the base of the tentacle and the large white blob is the foot, with the propodium curling towards the head, looking for some substrate to grab onto.  It's hard to see that the penis is distinct from the neck in this photo. It is a lot easier to see when the animal is moving around in front of you.

Female snails have...
                                    .... lots of ducts and glands.  These structures are integrated into the mantle, on the anterior right side near the head.  The capsule gland and albumin gland play an important role in the packaging of eggs into capsules.  In Crepidula species the reproductive system ends in a female genital papilla (fgp) which extends into the mantle cavity.  This is the tube through which the eggs are extruded.  In Crucibulum and Calyptraea there is not fgp and it's more difficult to tell the sex of live snails.  


Here you can see the fgp of a Crepidula incurva. It is attached to the mantle cavity and extends into the mantle cavity.  




If you take female slipper shells out of the shell you will see something like this. The red arrows point to the capsule and albumin glands. In "B." the mantle is reflected and the gill is sticking out to the right.  In this case the animal does not have an fgp but if it did, it would be projecting out near the arrow on the right.

Transitioning
In slipper snails sex change happens gradually.  The snails always start life as males and change later to become females.  During the transition the males slowly lose the penis and the female glands and ducts slowly develop.  It is possible to find sexual intermediates that have both a penis and an fgp, and to find intermediates that lack both of these structures.  

You can read about some of our experiments with sex change in these publications:



Collin, R.,  M. McLellan, K. Gruber, and C. Bailey-Jourdain.  2005.  Effects of conspecific associations on size at sex change in three species of calyptraeid gastropods.  Marine Ecology Progress Series 293:89-97 [reprint]

Mérot, C. and R. Collin.  2012.  Effects of food availability on sex change in two species of Crepidula (Gastropoda: Calyptraeidae).  Marine Ecology Progress Series.  449:   173-181.   [abstract] 

Mérot, C. and R. Collin.  2012.  Effects of stress on sex change in Crepidula cf. marginalis (Gastropoda: Calyptraeidae).  Journal of Experimental Marine Biology and Ecology.   416-417:  68-71. [abstract]



Thursday, August 1, 2013

Something Crazy Washed Up

We go frequently to the intertidal near the town of Veracruz, just outside Panama City. We see lots of things washed up along the drift line.  Mostly garbage like flip-flops, diapers and plastic bags.  Sometimes shells and fish bones.  But once in a while there is something a little more interesting.

Here's something crazy Matt Starr and I saw in the intertidal a little while ago.





It looks like its defenses backfired on this pufferfish. It must have puffed up and got stuck in the predator's mouth.  

When they are not puffed up (lacquered and hanging from the ceiling of tacky bars), puffers look chunky, but not balloon-like.   Here is a happy one I photographed in Coiba.



It seems that this is not the only time a puffer's defenses didn't work out very well.  I've seen a dead puffer lying in a cemetery (how appropriate) more than a mile from the sea.  I imagine that it was dropped by a seabird, unfortunately for the puffer, not over the ocean.

Friday, July 26, 2013

Scoping Out Larval Diversity in Bocas del Toro

Does spending two weeks in a tropical paradise in the lab with your eyes glued to the microscope sound like fun to you?


Two weeks looking through the microscope - exactly what the participants of the "Larval Invertebrates: Diversity, Form and Function" workshop did in July.  In fact students and instructors came from around the world for this chance to develop eye-strain and miss out on getting a tan.  

Well, it does to larval biologists - scientists who study the beautiful and diverse developmental stages of marine invertebrates and fishes.  In July we held a workshop at STRI's Bocas del Toro Research Station, focused on the diversity of invertebrate larval forms. Here's a little bit about what we did.

We started the day with a short (30 minutes, or maybe an hour) trip to the field to collect samples, using plankton tows.  Nets with a tiny mesh size of 0.125 mm catch the larvae and many other small organisms.  We let the boat drift slowly while we tow to stop the delicate organisms getting mashed against the sides of the net.  
Marco carrying samples up to the
laboratory.


The group setting off from the dock.


Bringing the net into the boat.













After the short field trip, we spent 6-8 hours looking through the microscope picking through all of the other planktonic organisms -- various microalgae, like diatoms and dinoflagellates, as well as gelatinous zooplankton like jellyfish and ctenophores -- to find the precious larvae.  The plankton in Bocas is so rich that 15 people can spend 6 hours each just to sort through the contents of 2 buckets.  It sounds tedious but it's like a treasure hunt -- you don't want to stop looking just in case something really exciting is in the next slurp of plankton.

Like caterpillars and butterflies, the larval stages of marine invertebrates usually look nothing like the adults.   In this case, however, the larvae are beautiful. Lovely. Delicate. They often turn into fairly mundane adults when they grow up. Usually worms you wouldn't look at twice, which give no hint of their ethereal appearance earlier in life.


Some of the larvae collected in Bocas del Toro.  Photos by Karen Chang and Michael Boyle.

For years, before scientists could match the larvae with the adult animals, the larval forms were given their own names.  Now we know that actinotrochs (top center) are larvae of phoronid worms, or mitraria (not shown) are larvae of owiniid worms (it all sounds like Greek - or Latin- doesn't it?).  The morphology can tell us it's a phoronid or a owiniid, but not what species or even what genus it belongs to.

We are trying to use DNA barcoding to match the larvae to the adults.  In collaboration with the LAB in the Natural History Museum, we will sequence the COI gene from 100s of larvae that the workshop participants picked from the plankton and photo-documented.  The results, when we get them later in the year, will be compared with published COI DNA sequences from adult animals.  This will tell us if larvae that look the same all actually belong to the same species.  For some groups we will be able to match larvae to adults for the first time, documenting the kind of development for many of these poorly studied tropical species.  Most exciting of all, we expect to find species where the adults have not yet been discovered or reported in Panama.  

To learn more about invertebrate larvae check out the fantastic blog from Svetlana Maslakova's lab at the Oregon Institute of Marine Biology.