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November 19, 1998

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.


Hawaiian honeycreepers and the molecular clock

One of the most useful gadgets in the geologist's tool box is the ability to measure the age of a lava flow, an island, or even the earth itself.

The techniques to do this involve studying processes, such as weathering, that indicate age. Measurement of chemical and radioactive changes can be used to date rocks. By dating geological features, one can reconstruct the course of events, such as how the Big Island was built.

Understanding geological events in Hawaii has proceeded at a faster pace than discovering the history of our native plants and animals. When did they get here? From where did they come? Until recently nobody has been able to "date" a species of tree fern or know when the first land bird arrived.

A way to start is by looking at how much a group of organisms -- let's say birds -- has changed. For instance, an `auku`u stealing fish out of Lokoaka pond near Kealoha Beach Park is identical in every way to the black-crowned night-heron overseas. Although this bird is native, perhaps it got here only recently, because it hasn't changed from its relatives elsewhere.

By contrast, an `io soaring over the Panaewa farm lots bears no resemblance to another hawk. It must have arrived a long time ago to have changed so much. But how long ago was that?

The answers have come recently by a now familiar biological tool, the analysis of DNA. Applying the same techniques that forensic labs use to identify criminal suspects from a piece of hair or a drop of blood, biologists are now mapping the DNA of birds. The principle here is called the molecular clock.

DNA is the giant molecule in each of our cells that holds the architectural plan of our body and physical functions. Over the generations, DNA changes at a presumably steady rate. For birds, that's about 2% change (for mitochondrial DNA) in a million years -- not a whole lot! But it's enough to figure out their evolutionary history. What have we found out?

The DNA samples come from a drop of bird blood or from bone of extinct species, some of them dead for a thousand years. By comparing the DNA of related species, biologists can construct a family tree. Most of the research on DNA comparisons for Hawaiian birds has been done by Dr. Rob Fleischer and his collaborators at the Smithsonian Institution. They have learned that the Hawaiian honeycreepers evolved from sparrow-like birds that made their landfall in Hawai`i about 4-5 million years ago, when Kaua`i was an active volcano and most of the rest of our state didn't yet exist.

The DNA shows that the original honeycreeper rapidly evolved into a large number of species, the descendants of which are still with us today. In some cases, the DNA also documents when a species colonized new Hawaiian islands as they emerged from the sea. Getting back to the `auku`u and the `io, DNA and the molecular clock would say that the heron reached Hawaii in the last few thousand years, and that the hawk arrived about a million years ago.

Eruption and Earthquake Update

The eruptive activity of Kilauea Volcano continues unabated. Lava flows through a network of tubes from the Pu`u `O`o vent to the sea. Several short-lived surface flows originated from breakouts of the tube system at the base of the pali. Lava is entering the ocean along a section near Kamokuna. The public is reminded that the ocean entry areas are extremely hazardous, with explosions accompanying frequent collapses of the lava delta. The steam clouds are highly acidic and laced with glass particles.

There were no earthquakes reported felt during the past week.

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Updated: 08 Dec 1998