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| ʻiʻiwi (Drepanis coccinea) Photo Credit: Scientific Frontline / stock image |
Scientific Frontline: Extended "At a Glance" Summary: The Hawaiian Honeycreeper Evolutionary Tree
The Core Concept: An international research team utilized advanced genomic sequencing to construct the first comprehensive evolutionary map of Hawaiian honeycreepers, resolving the complex relationships among living, extinct, and fossilized species.
Key Distinction/Mechanism: By successfully extracting and sequencing genetic material from minimally invasive epidermis samples of museum skins and ancient fossil bones, researchers accurately traced lineage relationships and confirmed historical hybridization (genetic mixing) events that typically obscure rapid diversification models.
Origin/History: Hawaiian honeycreepers evolved from a single ancestor, experiencing a "big bang" of adaptive radiation approximately 2.5 to 3.5 million years ago, coinciding with the formation of the island of Oahu. Of the lineages present during European arrival in 1778, only 17 species survive today.
Major Frameworks/Components:
- Adaptive Radiation: The rapid diversification of a single ancestral lineage into numerous new species occupying distinct ecological niches.
- Paleogenomics and Museomics: The recovery and analysis of DNA from historical natural history specimens and paleontological bone fossils to reconstruct evolutionary timelines.
- Introgressive Hybridization: Confirmed genetic mixing between distinct species, such as the extinct 'ō'ū (Psittirostra psittacea) and the Lāna'i hookbill (Dysmorodrepanis munroi), as well as ongoing gene flow among 'amakihi (Chlorodrepanis spp.) populations.
Branch of Science: Evolutionary Biology, Genomics, Paleontology, Conservation Biology, and Ornithology.
Future Application: The genomic data generated will guide future research into the morphological evolution of honeycreepers and identify specific genomic variations that may confer resistance to introduced, devastating pathogens like avian malaria and avipoxvirus.
Why It Matters: Clarifying these evolutionary relationships uncovers a more extensive history of lineage loss than previously known, aids in understanding past biodiversity collapse, and establishes critical, data-driven conservation priorities to protect the remaining threatened honeycreeper species.
Dr. Natalia Przelomska, from the University's Institute of the Earth and Environment, was part of an international team led by scientists from the Smithsonian's National Zoo and Conservation Biology Institute (NZCBI) and the National Museum of Natural History.
The study, published in the Proceedings of the National Academy of Sciences, places both extinct and living Hawaiian honeycreeper species into their evolutionary context, helping scientists better understand biodiversity loss and informing future conservation priorities.
More than 60 Hawaiian honeycreeper species evolved from a single ancestor on the Hawaiian Islands over a relatively short period, making them one of the world's best examples of adaptive radiation—the rapid diversification of one species into many new ones.
However, rapid diversification can make it difficult to reconstruct evolutionary relationships accurately. Today, that challenge is especially important because only 17 Hawaiian honeycreeper species remain, with most threatened by habitat loss, introduced diseases, invasive predators, and climate change.
To address this, the international research team used advanced genetic methods to resolve the relationships among the 17 surviving species, along with 18 species that were still present when Europeans first arrived in Hawaii in 1778 and two additional species known only from fossil remains.
Lead author Michael Campana, genomicist at the Smithsonian's National Zoo and Conservation Biology Institute, said, "The findings are bittersweet because while we have a much better understanding of the relationships among the Hawaiian honeycreepers and the role hybridization played in their evolution, they also show we have lost more Hawaiian honeycreeper lineages than we previously knew."
The research team presents the first comprehensive map of the Hawaiian honeycreeper radiation. They found that most species originated during a "big bang" of diversification that took place approximately 2.5 to 3.5 million years ago, around the same time that the island of O‘ahu formed.
The team speculates this period facilitated a burst of diversification among honeycreepers because the new island afforded them unoccupied habitats with room to form multiple, distinct populations that then contributed their new genetic material back to other lineages on older islands. While breeding between two animals of different species is often a genetic dead end, the team confirmed genetic mixing between two honeycreeper species, the ‘ō‘ū (Psittirostra psittacea) and the Lāna‘i hookbill (Dysmorodrepanis munroi), and that a group of closely related honeycreepers called ‘amakihi (Chlorodrepanis spp.), which occupied different islands, continues to share genetic material today.
Researchers were able to gain a fuller understanding of the honeycreeper radiation by using minimally invasive techniques to collect samples from living and extinct species held in museum collections across the United States and Europe. They also successfully recovered genetic material from fossil bones, demonstrating the growing importance of museum and paleontological specimens for genomics research.
"I marvel at the amount of genetic data that my colleagues recovered from tiny bits of epidermis cut from old museum specimens of extinct honeycreepers," said Helen James, curator of birds and chair of vertebrate zoology at the Smithsonian's National Museum of Natural History.
"They even succeeded at getting genetic data out of small fossil bones of the honeycreepers. This really highlights how improvements in genetic sequencing have transformed traditional natural history museum collections into vast repositories of historical and comparative genetic information. This is especially true for birds and mammals, which were often preserved in the form of dried skins and bones, and we are now good at getting DNA from those types of specimens."
The team is now investigating the impacts, evolution, and control of introduced diseases, including avian malaria and avipoxvirus, which have devastated honeycreeper populations. They hope to better understand how both the birds and the pathogens have evolved since the diseases were first introduced to the islands.
Senior author Robert Fleischer, scientist emeritus at the Smithsonian's National Zoo and Conservation Biology Institute, said, "The genomic data we generated for this study should also be useful for understanding the morphological evolution of the honeycreepers, as well as to offer clues about how the genomic variation of some honeycreeper species may have influenced their ability to survive disease."
Reference material: ʻiʻiwi (Drepanis coccinea): The Metazoa Explorer
Published in journal: Proceedings of the National Academy of Sciences
Title: Reticulated adaptive radiation and phylogenomic diversity loss in the Hawaiian honeycreepers
Authors: Michael G. Campana, Madhvi X. Venkatraman, Mirian T. N. Tsuchiya, Anna M. Kearns, Nichelle M. VanTassel, Amberleigh E. Henschen, Natalia A. S. Przelomska, Nancy Rotzel McInerney, Margad-Erdene Ochirbat, Heather R. L. Lerner, Taylor E. Callicrate, Molly Hagemann, Eben H. Paxton, Loren Cassin-Sackett, Helen F. James, and Robert C. Fleischer
Source/Credit: University of Portsmouth
Edited by: Scientific Frontline
Reference Number: ebio080426_01