Invertebrates in the news #3 - A new tree of life for the Arthropods

You may not have heard of the word "arthropod" but you are certainly familiar with at least some members of this group: the insects. While insects make arthropods the most diverse phylum, arthropods also contains many other groups. Arthropods can be tiny (fleas) or fairly large (lobsters). They live in a variety of habitats: from the polar waters (krill) to the top of the trees (beetles) through arid deserts (scorpions).

On top of this diversity, arthropods are also economically important. For instance, mosquitoes carry the parasite which causes malaria, bees pollinate many of the fruits we eat, and the fruit fly is a model organism for genetic and medical research. Understanding how different groups of arthropods are related helps understand their evolution.

Scientists have been trying for a long time to understand how the different groups of arthropods are related to each other using morphological characters. This is not an easy task because arthropods are an ancient group. They appeared some 550 million years ago and all the extant groups were formed at least 200 million years ago. This is plenty of time to accumulate morphological differences which may mask the true relationships among extant groups.

This week, the journal Nature published a study that used an unprecedented amount of information found in DNA to understand how the major groups of arthropods are related. The results elucidate some long-debated issues about the relationships among various groups of arthropods. I highlight here two main findings.

Simplified Arthropod phylogeny based on Regier et al (2010)

First, the authors confirm the results of previous DNA-based studies showing that the myriapods (the group which includes the centipedes and the millipedes) are not directly related to insects, and thus, that these two groups invaded land independently. It has been proposed that myriapods and insects were closely related because they both used special organs to breathe air. Furthermore, the myriapods are not directly related to the Chelicerata (spiders, scorpions, horseshoe crabs, mites, ticks) but belong to the Mandibulata (all the other arthropods).

A pycnogonid from Lizard Island, Australia

Second, the closest relatives to the insects are a group of rare arthropods that the authors grouped under the new name of Xenocarida ("strange shrimps"). This new group unites two classes of arthropods that have only been recently described. In particular, the Remipedia were described in the 1980's and are only known from a few places (the Bahamas, the Canary Islands, Mexico and Cuba) where they live in caves. This illustrates the issue of what is called "taxon sampling" when scientists try to infer the relationships among organisms. If the authors didn't include these groups, the conclusions of their study would have been different, and some other arthropod group would have been mistaken for being the closest relatives of insects. Furthermore, it also illustrates the importance of habitat conservation and field work to preserve and discover species that can help unraveling the tree of life.

Link to the study:

• Regier et al, 2010. Arthropod relationships revealed by phylogenomic analysis of nuclear protein-coding sequences. Nature.

More blog articles about the study:

• The most ambitious arthropod phylogeny yet -- by Alex Wild at Myrmecos blog
• Blind Cousins to the Arthropod superstars -- by Carl Zimmer at The Loom

New Arrivals

After the grant report was due, we all heaved a sigh of relief but didn't stop to rest on our laurels. Instead we hit the ground running. Sarah and Jenna pitched in to help me take care of some of the stuff on and around my desk, mostly the ever-growing piles of re-IDs. Thanks goodness for their help...

Am I laughing or crying behind subsample mountian? It could go either way. Oh the humanity! But we finished the grant right? Why is my pile of re-IDs still growing? Pictured below is why.

Art has abandoned the Nart consortium and joined the Shrimp Mafia. He has recruited Sammy DeGrave and Ivan Marin to work with him on shrimp identifying. They will be visiting us for several weeks.

Remember that little trip to Heron Island that Rob, Sea, and François went on? Well those specimens (seven buckets worth) arrived from Australia to make the week more interesting. Since it was so long in transit without ethanol it needed our immediate attention. Jenna did the lion's share of the unpacking and rehousing.

But I (along with Sarah, not pictured--don't worry, I make up for it later) totally helped.

There was so much material that we had to make multiple trips to the offsite ethanol storage facility (hereafter known as the Ethanarium) to refill our supply back at the range. Here is Sarah multitasking by refilling our ethanol carboy and getting a tricep workout.

Sarah has also been doing some work in the lab with Jodi, a grad student in Entomology/Nemotology who is doing some land snail work with John. Even though we send much of our DNA work to the Smithsonian, for our more immediate and smaller-scale needs we can still do extractions here. Sarah has been showing her our procedures.

Plus, we also rested on our laurels. In the picture below you can see the celebratory feast we prepared and a portion of the celebrants (from right to left): John, Nat, Gustav, Sarah, Sea, Mika. But what's that poking out from behind the tree?

Puppies! It was also Mookie's birthday on Feb 1st. End of grant and puppy birthday, what better reason to feast! Gustav, Sarah, and I all brought our pups: Puka, Motu, and Mookie.

Now back to work!

:) Mandy

Invertebrates in the news #2 - David Liittschwager's images in National Geographic

For this second edition of invertebrates in the news, I chose to follow up on a previous post. In early December, Seabird reported on David Liittschwager's visit in Moorea. As announced at the time, the pictures he took during his visit are published in the February issue of National Geographic.

The photographs illustrate a feature article written by E. O. Wilson that emphasizes how important -- and yet little known -- are the small organisms that live in the soil, in the sea, around us. To unravel some of this diversity, David Liitschwager went to six different ecosystems around the globe, and carried with him a green metal-frame cube. At each location, he observed and took pictures of all the organisms he found in his one cubic foot cube. For each location, there is also a video showing how he proceeded.

If so many forms of life can fit into one cubic foot, it means that in order to fully appreciate the diversity of life one must also look closely for the smaller organisms.

Grant-ed

We (meaning Gustav) had a grant report due on January 31st so we have spent the past few weeks making sure that we had dotted and crossed our i's and t's respectively. A grant report is often required at the end the term of a grant, and it is our opportunity to show the funding agency how the money was spent and how we kept all the promises that we outlined in the original grant application. In our case this called for some last minute plating just to make extra sure that we would have as many as we promised. Lots of people got in on the act. Jenna is a veteran plater, and you've already seen her mad skills immortalized in digital format. Less accustomed to plating, but still lending much-needed manpower to the task, is the Nat/Art consortium which we have named Nart. Nart tag-teamed several arthropod plates.

Because mollusc shells are sometimes broken (either accidentally or by necessity) to get a subsample of the animal's tissue, we photograph the specimen before sampling so we have a photo voucher of the intact animal. Sarah is the speediest photographer in the west so she often manned the photo station.

While some of us spent countless hours plating, it wasn't the only activity in the range. It's a new semester so Gustav put out the call, "CUKE TEAM! ASSEMBLLLLLLLE!" is what I'm sure the email said. And assemble they did. Here they are meeting to discuss strategy. I'm pretty sure that the strategy involves a lot of ossicle slide preparation on the part of Julie, Laura, and JD.

Several members of our lab also went to the Florida Union of Malacologists meeting in Sanibel this past weekend. John, Gustav, Fred, Jim, and Chelsey all presented talks. They are also featured in the group photo, along with several people whom you might recognize from their visits to the museum.

In the face of the plating challenge, I have been neglecting my desk for the past week. Emails with work requests have piled up as well as boxes of vials and supsample tubes to be cataloged or renamed in the database. This is what faced me on February 1st.

To those who would be tempted to suggest that my desk always looks like this I would argue that flinging accusations around doesn't empty my desk any faster, and if you're not part of the solution then you're probably part of the problem. Even though February has just begun, we have quite a month lined up. Stay tuned.

:) Mandy