NEW YORK (GenomeWeb News) – A group of extinct Hawaiian birds called honeyeaters evolved independently from very similar nectar-feeding birds in Australia, New Guinea, and other parts of the Pacific, a new sequencing study suggests.
Researchers from Washington’s Smithsonian Institution uncovered the case of convergent evolution by sequencing nuclear and mitochondrial DNA from 115 to 158 year old Hawaiian honeyeater specimens. Their results, appearing online yesterday in Current Biology, suggest all five Hawaiian honeyeaters species were related to each other — but not to the Australasian honeyeaters. Instead, the extinct birds appear to have been most closely related to groups of fruit and insect-feeding birds.
“They’re in a totally different part of the songbird tree,” lead author Robert Fleischer, an evolutionary genetics and vertebrate zoology researcher affiliated with the Smithsonian Institution’s National Zoological Park and National Museum of Natural History, told GenomeWeb Daily News. “This was probably the most bizarre finding we could have expected.”
Joel Cracraft, an ornithologist and curator in charge of the American Museum of Natural History’s department of ornithology, who was not involved in the study, called the results an interesting example of convergent evolution and predicted that the work will generate buzz.
“It’s a really nice paper,” Cracraft told GenomeWeb Daily News. “This is an important result — certainly for ornithologists and probably for evolutionary biologists in general.”
Five honeyeater species in two genera, Moho and Chaetoptila, lived on Hawaii’s islands until their extinction between the 1850s and the mid-1980s. Their morphology, behavior, and ecology closely resembled that of the 182 honeyeater species living in Australia, New Guinea, and the Pacific Islands. Consequently, the five Hawaiian species were traditionally classified with Australasian honeyeaters in the Meliphagidae family.
Fleischer started working on honeyeater classification about a decade ago, with the goal of determining where Hawaiian honeyeaters fell within the larger honeyeater group. After some investigation, though, he began realizing that it wasn’t possible to neatly classify the Hawaiian birds within Meliphagidae based on their mitochondrial DNA. “It didn’t work,” Fleischer said. “I realized that something was fishy.”
For the latest paper, he and his colleagues collected honeyeater genetic data more broadly, assessing both nuclear and mitochondrial sequence from eight Moho museum specimens and a single Chaetoptila specimen. The team also looked at DNA sequence from a Samoan meliphagid called Gymnomyza samoenisis and from a crow.
Using 1,923 base pairs of nuclear DNA from three nuclear genes and 717 base pairs of mitochondrial DNA representing 12S RNA, cytochrome b, ATPase6 and ATPase8 genes, the team did phylogenetic analyses, comparing the Hawaiian honeyeaters with other bird groups.
The team found evidence that the five Hawaiian honeyeater species were related to one another. But the birds didn’t fit into the Meliphagidae family tree with the Australian and Pacific honeyeaters as expected.
Instead, the birds landed on another branch of the tree entirely, Fleischer explained, “in with a group that are kind of an odd bag of things that are spread out all over the place.” The results suggest Hawaiian honeyeaters were most closely related to three passerine bird families — waxwings, New World silky flycatchers, and palm chats — that eat fruit and/or insects.
From this data, it seems Hawaiian honeyeaters’ ancestor came from the Holarctic or Neotropical regions rather than the South Pacific. The research also places the birds in a new family, dubbed Mohoidae.
That means the similar adaptations to nectar feeding observed in the Hawaiian and Australasian honeyeater groups are a consequence of convergent evolution. This convergence was so complete that both the Hawaiian honeyeaters and their Australasian counterparts independently evolved three similar morphotypes in each region.
Based on the current nuclear DNA data, the researchers estimated that Hawaiian honeyeaters diverged from their closest relative between 14 million and 17 million years ago, around the same time bird-pollinated plant groups arrived in Hawaii.
He noted that more research is necessary to more clearly sort out both the evolutionary history of the birds and relationships between species. For his part, Cracraft said he believes the results reported in the paper will hold up, but also said more work is required to tease apart the relationships between species in the Hawaiian honeyeater group.
Fleischer and his team are currently sequencing more mtDNA in an effort to do just that. He and his co-workers are also interested in more precisely resolving the birds’ place in the phylogenetic tree and finding their closest relative.