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.