Monday, October 27, 2008

Hawaiian lobelias--all from a single original immigrant

The Hawaiian archipelago is not renowned for its spectacular native flowers, but it has them, and some of the most breathtaking examples are in the lobelia family.
From amazing spires of ivory blooms that rise from low rosettes of green to drooping delicate lavender showpieces that dangle from tree forms.
(Image: A yellow-flowered Brighamia insignis—another of the amazing range of lobelias in Hawai'i. Credit: Forest and Kim Starr.)
Purples and pales are the lobelias' favorite colors, but the range is enormous.
So, where does all this diversity come from in an island chain so isolated.
From a single introduction, 13 million years ago, according to a new study published in the Proceedings of the Royal Society B, “Origin, adaptive radiation and diversification of the Hawaiian lobeliads.”
Its authors are Thomas Givnish, Kendra Millam, Thomas Paterson, Terra Theim, Jillian Henss and Kenneth Sytsma, all of the University of Wisconsin at Madison, Austin Mast of Florida State University, Andrew Hipp of Illinois' Morton Arboretum, James Smith of Idaho's Snake River Plains Herbarium, and, in Hawai'i, Kenneth Wood of the National Tropical Botanical Garden.
Their research updates earlier arguments that lobelias in Hawai'i must have come from multiple introductions.
The lobelia's 126 species in six distinct genus groups, represent an eighth of all the native plant species in Hawai'i. And, say the authors, “have long been viewed as one of the most spectacular examples of adaptive radiation in plants.”
Perhaps the most spectacular.
“The Hawaiian lobelias are the most species-rich radiation of plants derived from a single colonist to be resolved on any single oceanic island or archipelago,” the authors write.
Looking into the genetic material in Hawaiian lobelias, the researchers concluded that the first one arrived long before any of the existing main Hawaiian Islands were even formed. Thirteen million years ago, the islands we now know as French Frigate Shoals, Gardner Pinnacles and Laysan were located where the current main islands are. With the northwest movement of the Pacific Plate, those islands now lie hundreds of miles away, in the middle of the Papahanaumokuakea Marine National Monument.
So the ancestors of modern lobelias, once they arrived here, hopped across channels as new islands formed, riding winds, riding currents, riding birds perhaps.
The source of Hawai'i's first lobelia remains unclear. The Hawaiian group's closest relatives are in Japan's Bonin Islands, elsewhere in Polynesia, and Africa. All are about equally closely related, so there is no clear front-runner in the guessing on which is the source.
The earliest arrivals appear to have been plants adapted to forests, grasslands and bogs, and certain kinds of lobelias seem to have evolved later to suit cliffside habitats and high-elevation environments.
Those earliest arrivals also seem to have been ones with wind-dispersed seeds. Over time, some of the lobelias developed fleshy fruits that were dispersed by birds. Once genus groups like the Cyanea did this, they couldn't move as far and began developing more different species than the wind-dispersed lobelias.
©2008 Jan W. TenBruggencate

No comments: