It’s a blob. It’s an animal. It’s Trichoplax

The irresistibly attractive Trichoplax. Oliver Voigt, courtesy of Wikimedia Commons

Timeline, 2008: One of the greatest quests in animal biology is the search for the “ur-animal,” the proto-creature that lies at the base of the animal family tree. For many years, the sponge held the low spot as most primitive animal, a relatively simple cousin of ours consisting of a few tissues and a tube that filters water for nutrients.

An animal, simple and alone

Research now suggests, however, that there’s an even older cousin at the base of the tree, an animal-like organism with three cell layers and four cell types that moves by undulating and exists alone in its own taxon. This organism, with the species name Trichoplax adhaerens, is the sole living representative of the Placozoa, or “flat animals.” It has been a bit of a mystery creature ever since the amoeba-like things were first noted a century ago in a German aquarium. Today, new techniques in systematics, the study of how living things are related, have helped pinpoint its place on the tree of life. These techniques have, however, left us with a few complex questions about this “simple” animal.

The animal kingdom family tree gets complex fast, with an early division in the trunk. Whatever lies at its base—and we’re still not sure what the organism was—that ancestor yielded two basic animal lineages. One led to sponges (Porifera) and branched to Cnidarians—corals, hydras, and organisms like jellies that have primitive nervous systems. The other lineage is the Bilateria, which includes everything from flatworms to bugs to beluga whales to us. Obviously, this lineage also has developed a nervous system, in many cases one that is quite complex.

Why a sponge will never be nervous

Earlier thinking was that the sponges, in lacking a nervous system, represented some earliest ancestor from which the two lineages sprang. But recent molecular analysis of the sponge and placozoan genomes has left a few systematists scratching their heads. The big headline was that the sea sponge was no longer the most primitive or oldest taxon. That honor may now belong to the placozoan, although some analyses place it as having evolved after Porifera.

An ur-animal? Or just another ur-cousin?

It may go a ways back, but it’s not so far that scientists can say that T. adharens is the “ur-animal,” or “mother of all animals.” In fact, it appears to share a few things in common with Bilateria, such as special protein junctions for holding tissues together, but computer analysis places it squarely in the Cnidaria branch of the animal family tree. Thus, this “weird, wee beastie,” while possibly older than the sponge, is still not the proto-ancestral animal condition. Rather than being the “ur-animal” from which all other animals sprang, it’s more like an “ur-cousin” of Bilateria.

Nervous system genes but no nervous system?

T. adhaerens also represents another conundrum for evolutionary biologists and systematists. It and the sponge both carry coding in their genomes for neural proteins, yet neither have nervous systems. The Cnidarian nervous system itself may have evolved parallel to that of the Bilateria, an evolutionary phenomenon known as “convergent evolution.” When evolutionary processes occur in parallel, unrelated species may share adaptations—such as a nervous system—because of similar selection pressures. The results are what we call “analogous structures,” which have similar functions and may even seem quite similar. But they are shared because of similar evolutionary pressures, not because of a common ancestry.

Lost traits make evolutionary biologists tear out their hair

The primitive placozoan does not have a nervous system, although organisms that arose later in the Cnidarian lineage, such as jellies, do. Yet those neural genes in its genome leave an open question and a continuing debate: Is the placozoan an example of another common evolutionary phenomenon in which a trait arises, but then is lost? Some scientists have suggested that there may have been an even older version of a nervous system, predating the Cnidarian/Bilateria split. This trait then vanished, leaving behind only these traces in the primitive placozoan and sponge genomes. With this scenario, the two nervous systems would have a shared ancestry: instead of being analogous traits resulting from convergent evolution, they would represent homologous traits, shared because of a common neural ancestry.


How Bumpy the Jelly eats without tentacles

Robot explores the deep sea

The deep dark layers of the sea—where sunlight doesn’t penetrate and oxygen levels drop as precipitously as the ocean shelves—may be home to some of the last great mysteries of our planet. New discoveries lie hidden in the depths, but it takes a robot to assist us in uncovering them.

The Monterey Bay Aquarium Research Institute in California has such a robot, Ventana, a deep-diving submarine robot that can roam the dark parts of the ocean where humans cannot go. In 1990, Ventana came across an unusual jelly(fish) in the mesopelagic zone, between 500 and 1800 feet down, where sunlight does not penetrate, but oxygen levels remain relatively high. This jelly was weird among its brethren. It had four fleshy arms that trailed behind its softball-sized gelatinous body (or bell), but no tentacles. Wart-like bumps covered its arms and bell, and as it moved through the water trailing its arms, it looked like a slow-moving meteor or translucent blue shooting star.

An elusive, warty marine invertebrate

Marine scientists at the aquarium were intrigued, but they felt they needed to find out more before introducing the jelly to the world. Over the next 13 years, they had only seven sightings of the animal, five in Monterey Bay, and two sightings 3000 miles away in the Gulf of California. It was the latter two, in 1993, that surprised them, because it demonstrated that the new jelly was not just a local creature endemic to Monterey Bay, but might have a wider distribution.

They captured at least one of the jellies, anxious to find out more about its habits. They placed their captive in a tank with small shrimp and pieces of squid and watched. The bits of squid and hapless shrimp collided with the bumps on the jelly’s bell and stuck there. Over time, the prey moved slowly down the bell, was transferred to one of the “arms,” and then slowly moved up the arm and into the mouth. The “arms” appeared to serve as lip-like extensions for prey, much as pseudopodia serve as prey-capturing extensions for some cells, like macrophages.

The jelly’s feeding mechanism was unusual, as were its choices in prey size. The animal probably dines on some of the many other jellies that inhabit its zone, and it appears to favor prey a little larger—at ¾ to two inches—than the average jelly prefers.

It’s a triple! A brand new subfamily, genus, and species!

Given these unusual characteristics, the scientists who made the discovery designated this jelly—which they had heretofore called “Bumpy” in honor of its appearance—a new subfamily, genus, and species. They assigned it the subfamily, Stellamedusidae, and gave it the species name Stellamedusa ventana. “Stella” derives from “star” because of the jelly’s shooting-star-like appearance as it moves through the water; “medusa” is a common name for jellies; and “ventana” comes from the robot submarine without which the researchers would never have made their discovery. This additional subfamily brings the total number of jelly subfamilies to eight and is quite a find; lions and housecats belong to the same family, but are in different subfamilies, so S. ventana is as distantly related to other jellies as the “king of the jungle” is to Kitty.

Patience: They waited 13 years to report this

Although the jelly is unusual among other jellies in lacking tentacles, the researchers who identified it and published a paper on their discovery in the Journal of the Marine Biological Association of the United Kingdom, say that several deep-sea species have evolved in a similar way, using “arms” instead of tentacles. The researchers waited 13 years to report their find because they wanted to uncover more information about S. ventana, but the creature still remains an enigma. In spite of its potentially wide distribution, it apparently has never turned up in fishermen’s nets and, with only seven sightings in 13 years, remains elusive.

The evolution of language

Language has families, too

We think of English as being a language distinct from, say, Hindi, but they both belong to the Indo-European family of languages. Family members include French, Spanish, German, and Walloon, spoken in a tiny area of France and by descendents of settlers in Green Bay, Wisc. Language, like genes, is passed on from generation to generation, and through time undergoes changes and additions, just as genomes do.

In the 1950s, a linguist named Morris Swadesh developed a field known as lexicostatistics, which studies linguistic family trees through quantitative analysis of a core group of words. These 100 to 200 words, known as Swadesh lists, identify the commonalities in any language, and according to Swadesh’s ideas, were thus less likely to change over time. To trace language lineages, Swadesh compared these groups for similarities and words—cognates—that appeared to have a common ancestor. The more cognates two languages shared, the more closely related they were presumed to be.

A fun word to learn: Glottochronology

In a study published in Nature, authors Russell Gray and Quentin Atkinson take the Swadesh approach into the realm of glottochronology, a way of determining the timing of divergence of languages. Based on their computations, they determined that the root of the Indo-European family tree traces back almost 9000 years ago to an area of what is now Turkey, where farmers grew crops and spoke Hittite. As they migrated, they took their languages with them. Gray and Atkinson’s findings counter another proposed origin of the Indo-European family tree, which posited that invading horsemen from the steppes of Asia brought their language with them as they prosecuted their warlike endeavors 6000 years ago.

What does this have to do with biology?

It is both inspired by and inspiring to biological evolutionary study. Swadesh developed his ideas at about the time that Watson and Crick were making their startling elucidation of DNA structure and copying mechanism. In their analyses, Gray and Atkinson used tools very similar to those biologists use to develop phylogenies to explore how species are related. Instead of gene or amino acid sequences, the authors used a series of letters that formed words; instead of identifying mutations, they identified changes in letters or syllables; and instead of orthologues—genes derived from a common ancestor—they identified cognates to elucidate relationships.

But Swadesh preceded biologists in one sense, in that he proposed using his analyses of Swadesh lists to determine time lapses as language developed and diverged; in other words, to use any divergences in cognates as a sort of clock to measure the time over which changes occur. One of the basic assumptions of this approach is that the changes will occur at a relatively constant rate when averaged out over time, giving a reasonably accurate assessment of how far back a relationship can be traced. This idea was only later taken up in biology as the idea of the “molecular clock,” in which biologists use the presumption of a constant rate of change in some gene or amino acid sequences to infer the timing of genetic divergence.

Problems with either approach

There are, of course, problems with either approach, and again, the problems are remarkably similar, whether the field is biology or linguistics. One common problem in building phylogenies is determining which changes occur because of environmental similarities (convergence), instead of relatedness; convergence is also an issue in the linguistic analysis, where words may appear to be cognates when they really are not. Another question that arises in biology is whether or not the genes being examined are suitable markers of evolutionary change; again, the same problem arise in linguistics—are words in the Swadesh lists, for example, suitable choices for comparison among languages? In spite of these inherent problems, Gray and Atkinson’s work has opened up fresh avenues of discovery and debate and brings biology and language closer to one another than ever.

Awww. Baby red panda

It was love at first sight for Shama and Tate, the red pandas at the Smithsonian’s National Zoo, and now, nearly 1½ years after they were introduced, the pair has a cub as evidence of their strong bond. On Wednesday, June 16, Shama gave birth to a single cub—the first for both of the Zoo’s red pandas (Ailurus fulgens) and the first red panda cub born at the National Zoo in Washington, D.C., in 15 years.

Red pandas have a baby. It’s very cute.

The National Zoo is celebrating its first birth of a red panda in 15 years. The history of the red panda–at least, of its classification–is complicated. More on that in a mo. What’s significant here is its current situation. Thanks to habitat loss, the species has declined in the wild to fewer than 2500 individuals, and it is endangered. So a birth–especially between an apparently happy couple with a strong mutual attraction–is a success for the zoo and for red panda conservation, too.

The proud mother was born at the Smithsonian Conservation Biology Institute in Front Royal, Va., and more than 100 surviving cubs have been born at both this research facility and the Washington, D.C., campuses since 1962.

Panda or raccoon?

Taxonomists–the folks who classify organisms by relatedness–have had a conundrum on their hands with the red panda. You’d think that the name says it all: it’s a panda, right?

Well, no. Nothing’s ever that easy in taxonomy. For some time, arguments that it was a relative of the raccoon held weight. But the animal has some strong panda-like traits, including an affinity for bamboo and similar habitats to the giant panda. But they differ in their far more diverse diet and greater habitat distribution.

The panda’s thumb

The giant panda has a faux thumb that’s really just a bone extension of the wrist bones. It’s not an opposable thumb like the one primates have, but the giant panda uses it in a thumb-like way. The red panda happens to share this odd trait. They also share many similarities in their DNA, which ended in the red panda briefly joining the bear family.

So, is it a panda or a raccoon?

The species also has some commonalities with the raccoon, including the ringed tail and more diverse diet compared to the giant panda, one that includes a taste for bird eggs. For these reasons, it also has been classified into the raccoon family. So, which family is it?

It’s neither. While the red panda has now been classified as a distant relative of the giant panda–the bamboo! the “thumb”!–it falls into its very own family, the Ailuridae, of which the red panda, or Ailurus fulgens, is the sole member. Unlike bears, this species arose in Asia and never made the trek to the “new world.”

Interesting note, the snow leopard–another severely endangered species–is their sole wild predator.

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