Sea Squirt Sperm Races

Botrylloides and Botryllus, originally uploaded by top.down.

Miriam at the Oysters Garter has an hilarious and informative post up about a quite serious subject, sperm size and reproductive success in broadcast spawners. Yes, size does matter! So does speed and quantity and...

The image above is from a researcher where I work study showing Botrylloides and Botryllus species of Urochordata. While neither Botrylloides nor Botryllus are endangered, (the topic of this weeks Life Photo Meme) these invasive colonial tunicates are endangering other benthic organisms. Of course the urochordata sexual habits have been discussed here before...

Classification for Botryllus schlosseri

Kingdom

Animalia

Phylum

Chordata

Subphylum

Urochordata

Class

Ascidiacea

Order

Pleurogona

Family

Botryllidae

Genus

Botryllus

Species

Botryllus schlosseri

Life Photo Meme

A Protocol for Sea Squirt Dissections

Our biology department has been having a lot problems keeping sea urchins alive here in landlocked central PA. Probably mostly from poor keeping, but they seem to be very sensitive to our wide temperature fluctuations (i.e. purple California sea urchins hate PA winters). As a back up we would like to use another organism when our urchins die off, possibly a Ciona species. Does any sea squirt biologists (Jarrett, Miriam?) have a protocol for dissecting gonad our of sea squirts? It is for a development lab. Please leave or a comment or email me (address in top right sidebar).

Sea Squirts, SLOSS and of Course Porn

Castilla et al. (2007) are reporting in a recent PNAS article an interesting property of sea squirt pornography and local oceanography. I know, I'm a frequent purveyor of tunicate smut, but this utter filth may have consequences in the debates surrounding marine reserve design. These authors studied the spawning behavior of intertidal tunicates (Pyura praeputialis, an invasive) from chilean coasts. What they found will make all decent folk turn their insides out. These filthy denizens of the seas let it all out together in a mass orgy. Oh the indecency. Are you sure the children are asleep and not watching over your shoulder? You may want to tuck them in before continuing on.

Sea squirts have mobile "tadpole"-like larvae whose role is typically dispersal since they do not feed. The also don't stay in the water column for too long, preferring to stick their heads to a rock somewhere (figure below shows larval metamorphosis).

Diagram from Cornell University's introductory biology autotutorial on chordates.

So what happens when tunicate sperm and egg meet seawater? An explosion of bio-foam! This foam is created by surfactants in Pyura's gametes (see figure below). This reduces the surface tension of the seawater. So basically, sea squirts spawn en masse, the high amount of gametes in tidal channels releases a high amount of surfactants which react with the seawater and its associated protein debris creating foam, the surface tension is reduced so larvae are not carried out to sea, thus larvae are retained in the tidal channel! As simple as that. Castilla et al. (2007) document the effects this foam might have on larval dispersal ability by monitoring ping pong balls in the channels. When there is no foam present, they all head out the channels to sea. When foam is present, 50-60% of the ping pong balls were retained in the tidal channel (depending on ebb or flood tidal conditions).

A) Mass splooging of P. praeputialis. B) Sperm (SS) and egg (ES) suspensions left dripping in the intertidal. C) 2 meters of foamy splooge. D) Chilean researcher knee-high in sea "squirt" if you know what I mean... Fig. 1 from Castilla et al. (2007).

So what is the end result of this filthy, spineless mass bukkake? (That ought to bring in the hits!) Larvae are retained in the tidal channels resulting in massive colonies over several generations. They are not trapped here though since theoretically, as shown with the ping pong ball experiment, nearly half of the larvae escape out to sea where they can start new colonies in other tidal channels perhaps. But this suggests that other larval forms are also retained during foamy times. Hence this bio-foam acts as resistor to the current of larvae out of a particular channel.

This has some interesting connotations for the ever debatable Single Large Or Several Small (SLOSS) dilemma facing marine reserve designers. If rare or endangered species occur in such tidal channels, for instance, you would want to grant protection to that channel. It is acting as quasi-reservoir for recruitments. Populations would appear to build up in these channels (excluding all other ecological forces that determine population size like competition, resource availability, etc.) and proportionally send out more larvae with each generation. This research suggests that protecting individually foamy channels (those with gametes secreting surfactants, or channels with high protein debris content) would more sufficiently protect the potential source of larvae for a particular species of interest. You just need to find the right areas, the foamy ones.

Of course this opens up a lot of questions. As someone interested in communities and diversity. I would like to understand how surface tension reduction affects the structure and composition of communities in foamy channels and compare that to non-foamy channels. Or, how planktonic communities respond to this potential stress? Does the composition of the seston track the cyclic patterns of the foam production and tides? Is diversity higher in non-foamy channels because foamy ones tend to have a higher dominance (and lower evenness) of a few species like Pyura praeputialis. Does the foam and reduced surface tension, act a barrier to immigration for new species and recruits? Its a pretty interesting system and though I don't know the foam literature well, I get a sense that this isn't well-studied. I will be looking for a postdoc very soon.... (hint hint).
____________________________________________________________________
Castilla JC, Manriquez PH, Delgado AP, Gargallo L, Leiva A, Radic D (2007) Bio-foam enhances larval retention in a free-spawning marine tunicate. Proceedings of the National Academy of Sciences 104:18120-18122. doi:10.1073/pnas.0708233104

Spineless Song of the Week - Sea Squirts Just Want To Have Fun

Photo of Clavelina dellavallei from Mer et Littoral - La Flore et la Fauna Marine l'Atlantique et de la Méditerranée

Inspired by recent research by Johnson & Yund that I posted on here, I transformed a classic Cyndi Lauper song into a Urochordata masterpiece. Well, thats for you to decide. If you don't know the song this is sung to, step out of the cave... Liquid courage brought to you this week by Dale's Pale Ale from the Oskar Blues Brewing Company.

Sea Squirts Just Want To Have Fun

I’m attached to rock in the moonlight
My colony says 'when you gonna live your life right?'
Oh but females aren’t the fortunate ones
And sea squirts, they want to have fun
Oh sea squirts just want to have fun

One sperm come in the middle of the night
My colony yells 'what you gonna do with your life?'
Oh ascidians, I can’t have only one,
But sea squirts, they want to have fun,
Oh sea squirts just want to have

(Chorus)
That's all they really want...
some fun...
When the filter-feeding day is done
Oh sea squirts they want to have fun
Oh sea squirts just want to have fun

Many males enter my siphonal canal
I don’t care how many, I’ve got eggs for them all
Some may say I’m too promiscuous
But sea squirts just want to have fun
Oh sea squirts just want to have

repeat chorus

Sea Squirt Chics Have No Inhibitions

Photo of Botryllus schlosseri from the Swalla Lab website
Yeah thats right they get it on with any male gamete that passes there way. They just give a [rhymes with duck]. Boom chaka-laka-boom. These loose lizzies are all about increasing genetic diversity if you know what I mean. OH, I know you know what I mean!

In the latest Molecular Ecology, Johnson & Yund, explore the promiscuity of tunicates (In order to preserve my somewhat kid-friendly stature, I won't even go into all the possibilities with sea squirts...but feel to in comments!). I like this study, not only for its obvious connotations, but because multiple paternity in a sessile critter is an interesting and fundamental research question. Most studies of promiscuity have focused on mobile fauna. But the uncanny Urochordata, Botryllus schlosseri, has another interesting facet, it alternates between being male and female, with no storage of sperm. Yeah, thats right. Being male is just a phase that Tunicates go through. But this does pose an interesting question.

Johnson & Yund used molecular tools, such as DNA microsatellites and sperm haplotyping to investigate the role of multiple paternity using three measures
1) minimum number of fathers, based on paternal allele frequency from embryos
2) number of sperm haplotypes
3) effective paternity, based on the number of unique sperm haplotypes

They found 15 sperm haplotypes and no effect of local or population level density on any of their measures. I find this interesting because common sense would appear to dictate that colonies would show skewing of sperm haplotypes towards males that are closest to the embryos of the females being sampled as opposed to sperm that has had to travel farther, hence becoming more diluted or fertilizing females closer by, etc. But this doesn't appear to be the case with Botryllus schlosseri from Maine's Damariscotta River estuary.

"The left side of a zooid of Botryllus schlosseri. The center of the system is to the right. Redrawn from van Name (1945). The North and South American ascidians. Bull. American Mus. Nat. Hist. 84:1-476, 31 pls." Taken from Invertebrate Anatomy Online.

So the punchline is that a whopping 90% of broods (using the most conservative measure) have multiple fathers. In fact, the smallest effective paternity from any one population was 2.4, meaning that there at least more than 2 fathers for each brood. Conversely, the highest effective paternity was 14.2! Woowee! Thats a virtual Orgychordata if you ask me! Keep in mind they only genotyped 15-20 embryos out of a potential pool of over 4,000 embryos in a broo.d. So I would definitely say that B. schlosseri is the slut of the invertebrates. But that is not without its potential advantages as outlined in the conclusion by the authors:

"Polyandry to increase genetic diversity is predicted to be favoured only (i) as a mechanism of inbreeding avoidance (ii) under situations of completely unpredictable environmental fluctuation (iii) when there is intense sibling competition, or (iv) when there is some cooperative or compensatory interaction among half-sibs."-Johnson & Yund 2007