Sea Urchin Genome Reveals Striking Similarities to Humans

Scientists already knew that the creatures, which resemble underwater hedgehogs, are one of only a few invertebrates (animals without backbones) on the human branch of the evolutionary tree.

Purple sea urchins feast on the remains of
a giant kelp in Carmel Bay, California.

Scientists have completed sequencing the genome of
the California purple urchin—revealing surprising
new information about just how
closely urchins resemble humans and
how vital a role the marine creatures play
in ocean ecosystems.

(credit : Photograph © Science)

But a new sequence of the California purple urchin's genome reveals that the marine creatures and humans bear a striking number of similarities. (See related photo: "Sea Urchin Genome Decoded".)

"Comparing all the genes of the sea urchin, it's actually quite similar to us," said George Weinstock, who led the sequencing project. Weinstock is co-director of the Human Genome Sequencing Center at Baylor College of Medicine in Houston, Texas.

The sea urchin is one of the few marine organisms whose genome has been sequenced. The study therefore also provides insights into the vital role of sea urchins in many marine ecosystems.

"Sea urchins are major grazers in shallow seas of many parts of the world's oceans ... and they are the main prey of many top predators," said John Pearse, a biologist at the University of California, Santa Cruz.

Results from the sequencing project and accompanying articles, including one by Pearse, will appear in tomorrow's issue of the journal Science.

Kelp Forests

Sea urchins, which feed mainly on algae, live in environments that alternate between species-rich kelp forests and sea urchin-dominated "barrens."

"They are known to limit sea grass and kelp production and consequently the diversity and complexity in communities supported by these producers," Pearse said.

He compares sea urchins to rabbits and other grazers found on land.

"Sea urchins are the main prey of many top predators—including crabs, lobsters, fish, and sea otters—that directly limit their abundance, comparable to how coyotes, hawks, and owls limit the abundance of rabbits," Pearse said.

With a diminishing population of sea otters in California's Monterey Bay, for example, the population of sea urchins has multiplied. The sea urchins are reportedly chewing up the kelp forest in the area and upsetting the ecosystem. (Related video: "Killer Whale Mystery at Monterey Bay".) There are other factors that influence sea urchins' ecological role, including interactions among different urchin species.

"Populations of some species tend to explode and devastate the communities they are in, while others rarely do so," Pearse said. "Knowledge of their genome might allow people to better understand the underlying mechanisms that lead to such differences."

Sea urchins can also be used by scientists to detect toxic chemicals.

"One of the things in the genome project has been to come up with a very detailed description of the defense mechanism that sea urchins have to deal with toxic chemicals," Weinstock, of Baylor College of Medicine, said.

"Understanding their sensitivities and resistances could potentially help fine-tune our use of them, in terms of understanding the marine environment."

Humans are also directly affecting sea urchin populations. Sea urchin roe, or ovaries, are a delicacy in Korea and Japan.

The U.S. sea urchin fishery has been in decline in recent years, however, because of reduced demand from Japanese consumers. (Related: "Seafood May Be Gone by 2048, Study Says"

[November 2, 2006].)

Human Cousin?

The urchin's usefulness as a model for developmental biology was another major reason for the sequencing project.

Scientists have long used sea urchins to study fertilization and early development in humans.

"The series of steps that happen after an egg is fertilized by a sperm ... those very early events turn out to be the same in the sea urchin as they are in the human," Weinstock said.

The scientists identified more than 23,000 genes in the 814 million base pairs, or "letters," of DNA code taken from the sea urchin.

The sea urchin represents the first sequenced genome from the echinoderms, which are the closest known relatives of the chordates, the group that includes vertebrates, animals with spinal columns.

The genome includes analogs to many essential human genes that were previously thought to be exclusive to vertebrates.

But missing among the sea urchin genes are some genes found in flies and worms. This, scientists say, shows that sea urchins are closer kin to humans than beetles, flies, crabs, and clams.

"Humans and sea urchins have a common ancestor," Weinstock said.

The eyeless sea urchin also has genes associated with taste, smell, hearing, balance—and surprisingly, even vision.

Source : http://news.nationalgeographic.com

Crustacean mesozooplankton - general information

Copepods

• Systematics & Phylogeny
  • Taxonomic Search via Smithsonian NMNH database
  • Harpacticoid phylogeny following Lang (Oldenberg site)
  • Calanoid phylogeny following Park and Andronov (Lucifer site)
  • 
    
• Biology
  • The Calanus Connection -- an account of Finley's observations on bowhead whales feeding on Calanus in Baffin Bay
  • Freshwater copepods and cladocerans of SW US: general info and lots of photos from Southwest Missouri State Univ.'s Zooplankton Project
  • SIO site: C. Fowler's Virtual Copepod Page: basics, images, animations, links, bibliography
  • Oldenberg site: Brief overview (no citations) of copepod biology
• Collections
  • Smithsonian collection at the National Museum of Natural History (searchable)
  • SIO's Planktonic Invertebrates Collection, including info on the Fleminger Copepod Library with 21,500 sorted specimens
• Links
  • SIO site
  • The World of Copepoda: Smithsonian Institution National Museum of Natural History's on-line data base
  • Links to web sites, maintained by Sean Avent.
  • Links to many web sites treating various aspects of copepod biology, maintained by Thorsten-D. Kunnemann (for parent site, click here).
  • Monoculus Library-- access to a library (real paper! ... not electronic) of copepod literature.
  • Monoculus on-line issues of Monoculus (Copepod newsletter connected to the International Congress on Copepoda)
  • Geoff Boxshall's pages, Natural History Museum, London
  • of Italy
• Research
  • Population-dynamics model of Calanus finmarchicus from Georges Bank region (C.B. Miller et al, 1998, Oregon State Univ.)
  • Calanus and Pseudocalanus distributions from Georges Bank (McGillicuddy & Davis, 1996)
  • Searchable database of copepod researchers via Smithsonian NMNH
• Grant award/report abstracts
  • Lake Michigan costal plumes project abstract (Vanderploeg & Bundy 1998)
  • Abundance, age-structure and ingestion rates (EPA award ending 1996, Roman, PI)
• Pictures
  • Aetideopsis armata (by April Davis)
  • Copilia vitrea (via Smithsonian NMNH's The World of Copepoda)
  • Euchaeta rimana (by Jeannette Yen)
  • Oncea venusta (NMNH)
  • Pleuromamma xiphias SEM done in psychedelic color (by Tina Weatherby [Carvalho])
  • Pontellina plumata (NMNH)
  • Sapphirina auronites (NMNH)
  • unknown sp. (calanoid)(by Uwe Kils)
  • Fresh water copepods of south-central US: photo album maintained by Southwest Missouri State Univ.
• Reference material
  • Bibliography search via Smithsonian NMNH database
  • The Biology of Calanoid Copepods by John Mauchline (Academic Press, 1998)
  • Copepod Family Euchaetidae by Taisoo Park (UC Press, 1995)

Cladocerans

• Links
  • Guelph site: Taxonomy, References, Researchers meetings, links
  • S.W. Missouri State site: General informationon clacoderans and fresh water copepods of south-central US, with lots of photos
  • DMOZ open directory project: links
• Pictures
  • Cladoceran photo album maintained by Southwest Missouri State Univ.

Amphipods

• Links
  • Old Dominion Univ. "The Amphipod Homepage"
  • Tromso Museum literature database by W. Vader
  • Southern Australian amphipods: general information
• Pictures
  • So. Australia photo gallery
  • Uwe Kils ecoscope photo

Ostracods

• Links
  • BMS Ostracod Group: links
  • Univ. of Iowa systematic index
  • USGS ostracode database
  • Bioluminescence and reproduction James Morin (Univ. of Calif., Los Angeles
• Pictures
  • Southern Australian ostracods: photo gallery

Zooplankton

by Prentice K. Stout

Zooplankton (zoon - Greek for animals and plankton, a word derived from Greek meaning wanders) are divided into two types: those that spend their whole lives as small plankton and those that drift as plankton only in their young stages. This second type will mature into various larger life forms.

Some of the permanent members of the zooplankton community are forminiferans, radiolarians, and copepods. The first two are roughly comparable to the diatoms and flagellates of the phytoplankton community. Forminiferans (hole-bearers) are organisms that live within small shells made of calcium carbonate, a substance similar to limestone, marble, and chalk. The protoplasm, a complex chemical "soup" found in living cells of all animals, flows out through the holes in their shells, forming a sticky, food-catching network.

As they outgrow their shells, the old abandoned ones are shed and the animal grows a new one taking the calcium carbonate from the surrounding water. Dead animals and discarded shells sink to the deep ocean bottom, there to be dissolved into calcium and carbon, available for reuse. In shallower waters, where this breakdown cannot take place, their remains built up thick layers called "globigerina ooze," named for the most common forminiferans, the globigerina. Over the 500 million years these animals have been in existence, and have been deposited on the ocean floor, forces have shifted the seabed and the presence of these new and ancient deposits of ooze has enabled scientists to estimate the age of such sedimentary deposits in different, separate parts of the world. This has given us a good fossil record. The chalk beds of Georgia and Mississippi as well as the white cliffs of Dover, England, attest to the vast quantities of these tiny animals.

Radiolarians are similar to their relatives, the forminiferans, both in skeletal shapes and protoplasmic food trapping ability. But their skeletons are made of a more resistant material called silica, a valuable filter and abrasive agent used in such products as toothpaste and for filtering certain liquids. Their bodies litter the ocean floor covering approximately 3 million square miles of tropical oceans. Copepods are so numerous that it is estimated that they compose seven out of every ten zooplankters. Their huge numbers have led some biologists to suggest that there are more of these animals in the world than all the multi-cellular animals combined.

Treading water by beating their limbs (from which they get their Greek name "oar-footed") as many as 600 times a minute, they use a vast amount of energy. this causes them to be ravenous eaters, having to consume their own weight in food each day. All of their food consists of phytoplankton. They are related to crustaceans, among whose members are crabs, lobsters, shrimp, and barnacles. For all their smallness, some large inhabitants of the oceans are dependent on them for food. The 45 foot long Basking Shark and the 60 foot long Whale Shark head the list of those in the oceanic food chain that feed on these copepods.

Dr. A.A. Benson, at the Scripps Institute of Oceanography, has stated that half of the world's photosynthetic product is converted, for a time, into wax by these tiny animals. Their fat is converted into a polyunsaturated liquid wax which is stored for the animal's use, but when the animal is eaten by sardines, herring, and anchovies, their wax is converted back into common fats by these large predators. Thus, we can see the importance of the copepod in the oceanic food chain.

Members of the zooplankton community migrate within the water column vertically each day. The phytoplankton, which do not migrate in this fashion are doomed to be wafted about the seas, by wind and waves. During the daylight hours, depending on the individual species preference, the zooplankters confine themselves to a narrow vertical range. As the fading light announces the onset of evening, the plankton begin a haphazard upward drift until, with night upon them, the entire zooplankton community is on the surface. Here they feed on phytoplankton and are in turn eaten by other larger species. As daylight approaches they drift down to their respective levels in the water column. The causes of this vertical migration have eluded scientists as to the precise answers.

We have mentioned zooplankton in the food chain. We can best illustrate this if we take 10,000 ponds of producers, the phytoplankton. This would support 1,000 pounds of first-order consumers or the zooplankton. IN turn this would support 100 pounds of second order consumers such as herring or anchovies. This would support 10 pounds of third order consumers such as the larger fish species, which would then support 1 pound of the fourth order consumers, for example, a seal. So we can see that for a seal to gain one pound, he would indirectly have to consume 10,000 pound of phytoplankton, the ultimate producers in the sea. Thus anything that interrupts this food chain can have serious consequences to the wellbeing of these consumers up the food chain ladder.

References

Hammer, William M. 1974. "Blue Water Plankton" National Geographic Magazine, October.

Gaskell, T.F. 1964. World Beneath the Oceans, The Story of Oceanography. The Natural History Press, Garden City, New York.