A newly released study by a Smithsonian Institution research group suggests that the association of ohia with island formation is more than myth.
“Progressive island colonization and ancient origin of Hawaiian Metrosideros (Myrtaceae),” published last week in the Proceedings of the Royal Society B, finds that the first ohia sprouted on Kauai while the island was still in its relative youth 3.9 million years ago.
From Kauai, or possibly blown across on the same wind currents that brought the first seeds to Kauai, ohia — Metrosideros species to the scientific community — sent its seeds across to the newly forming lands. The plant itself evolved into distinguishable species, although each of the species also is capable of significant variability in adapting to the wide range of microclimates occurring in the islands.
Still, by analyzing the genetic makeup of 97 plants collected from different regions of the islands and comparing them to 10 other Metrosideros from around the Pacific, the Smithsonian team found evidence of an ancient legacy and evolutionary diversification that coincided with the evolution of bird and insect species endemic to Hawaii.
The Hawaiians recognized the unique elements of this plant as well as its association with recent lava flows. That led to the association with Pele and ranked ohia among the sacred plants.
Its flowers can vary from a brilliant scarlet to yellow, and it adapts to high montane bogs and windblown coastal cliffs as well as to dry leeward slopes. At maturity, the ohia can vary from a majestic 100-foot rain forest tree to a 4-inch swamp dwarf.
Various legends say the ohia lehua is sacred to Pele and warned that anyone gathering the lehua for lei needed to be careful that they were not caught in an enveloping mist or sudden rain when picking them.
Otto Degener in “Plants of Hawaii National Park” noted the ability of the ohia to establish itself epiphytically on the ferns that are among the first plants to grow in new lava, eventually strangling the host while its roots tap the nutrients of the decaying fern.
The age of the ohia in Hawaii is significant to the natural history of the islands since so many species of birds and insects have evolved to be dependent on the ohia as part of their habitat. A number of endemic honeycreepers rely on the nectar of the ohia lehua, while several endemic insect species are specialized to the ohia bark, leaves and flowers.
“The arrival of Metrosideros in the archipelago and its dispersal to the new islands may have been a stimulus to evolutionary diversification in those lineages, in which case evolutionary events in the bird and insect lineages will correlate with the dispersal history of Metrosideros,” the study said.
The study said analysis of the processes that occurred can help in understanding adaptive radiation and the development of so many unique species in the islands.
Helen James, a member of the Smithsonian research team, said the first ohia plants on Kauai are believed to have sprouted from windblown seeds of Metrosideros from the Marquesas, based on the similarity in genetic makeup of the species in Hawaii and the species found in the Marquesas. The genetic dating of the evolution of the Hawaii species makes clear that the ohia arrived in Hawaii millions of years before the first Hawaiian did.
James said the primary credit for the study goes to researcher Diana M. Percy, who was lead author of the paper. Percy is with the Smithsonian Institution’s National Museum of Natural History and the Center for Conservation and Evolutionary Genetics.
“She spent a tremendous amount of time in the genetics laboratory examining the more than 100 samples. She examined 8,000 base pairs from the chloroplast genomes and looked at the amount of genetic variability and the correlation with how old the island was,” James explained.
The analysis involved comparison of the genetic differentiation among plants on each island and among the islands. This resulted in several unexpected findings beyond the age of the first colonization of Hawaii by Metrosideros.
Previous estimates had been that ohia first arrived just one million years ago, after the islands were already well formed.
According to the study, the team found 35 haplotypes among the plants in Hawaii, with only one found on more than one island — on Molokai and Oahu. Haplotypes are differences in a chromosome that may be passed to descendents in new arrangements through the recombination process of sexual reproduction. Diversity of haplotype can reflect genetic distance — how many generations have occurred from an original set of parents.
While the study said haplotype diversity, the amount of genetic differentiation among plants, was highest on Kauai, it also said there was no significant correlation between haplotype diversity and the age of the islands because of a “complex population structure found on some islands.”
“Molokai has a higher than expected haplotype diversity for its age (1.8 million to 2 million years) due to the occurrence of multiple haplotypes that may have derived from both older and younger islands,” it said.
“By contrast, Maui, with a monophyletic, nearly homogenous haplotype group, has a lower than expected haplotype diversity for its age (1.2 million to 1.5 million years).”
James explained that Molokai plants showed evidence of being related to plants found on other islands, while Maui plants appeared to be all closely related. She said the research team is familiar with the geological connections of Maui Nui — that Molokai, Lanai, Kahoolawe and Maui were all a single island possibly 1 million to 2 million
years ago. “That was the mystery. We didn’t find the Maui genotypes on Molokai, which is what we would have expected. We found Molokai had genotypes for Oahu, Kauai and even the Big Island. Maui had only its tightly knit group,” she said.
The full citation of the study is “Progressive island colonization and ancient origin of Hawaii Metrosideros (Myrtaceae),” Proceedings of the Royal Society B. Authors: Diana M. Percy, Adam M. Garver, Warren L. Wagner, Helen F. James, Clifford W. Cunningham, Scott E. Miller, Robert C. Fleischer.
• Edwin Tanji can be reached at firstname.lastname@example.org.
The showy, feathery blossoms of the ohia lehua supply nectar to many species of native birds, and the leaves and bark are host to native insects.
JACK JEFFREY photo