Saturday, September 13, 2014

On the big island, the first honeycreeper hybrid, between the redbirds `i`iwi and `apapane

There is a new native Hawaiian bird in the forest, a cross of two of the brightest jewels of the Island landscape—the red `i`iwi and the red `apapane.

(Image: The first-ever cross between an `i`iwi and `apapane. At left an `i`iwi, at right an `apapane, and at center the hybrid. All photos by Olga Lansdorp, courtesy of the authors.)
The unusual bird was caught in 2011 in the Upper Waiakea Forest Reserve on Hawai`i Island, and released after being banded. A DNA analysis performed on a single feather taken from the bird confirmed that it was the first-known cross of the two native honeycreepers.

A study on the find was published in the Wilson Journal of Ornithology by authors Jessie Knowlton of the Michigan Technological University and the Smithsonian Conservation Biology Institute, David Flashpohler of Michigan Technological University, and Rotzel Mcinerney and Robert Fleischer, both of Smithsonian Conservation Biology Institute. (The Wilson Journal of Ornithology 126(3):562–568, 2014)

The paper is entitled, “First Record of Hybridization in the Hawaiian Honeycreepers: `I`iwi (Vestiaria coccinea) x `Apapane (Himatione sanguinea).” The abstract is here.

Two key questions, of course, are opposite sides of the investigation: How did this happen, and why didn’t this happen before? With Darwin’s Galapagos finches, such crosses between species are known to occur. In Hawai`i, until now, they have not been known to happen.

“Our discovery is important in light of recent evidence that introgression and hybridization play important roles in speciation, maintenance of genetic diversity, and the movement of advantageous alleles within and between species,” the authors write.

DNA testing found that the bird’s mother was an `i`iwi and the father was the `apapane. 

The bird looked a little like both parents. Its size was closer to that of a male `apapane. Its color, based on a photograph with the paper, seems intermediate between the bright red of the `apapane and the orange-red of the `i`iwi. 

But its bill showed the combination most clearly. The `i`iwi has a long, curved, orange-colored bill. The `apapane has a short, black bill. The hybrid bird has a longish, curved bill about halfway between the lengths of the parent bills, and black in color.

The bird is a male, and the analysis could not determine whether the it was capable of reproducing. 

“This individual is the first hybrid ever confirmed for Hawaiian honeycreepers, despite ongoing study of these species for (more than) 40 years with thousands of individuals captured and banded and many thousands of specimens collected for museums,” the authors write.

Hawaiian honeycreepers are all believed to have evolved from a single parent bird, developing into an amazing range of colors, beak types, food preferences and habitat requirements. The `i`iwi and `apapane, then, are very distant cousins—genetic work suggested the species diverged from each other 1.6 million years ago. 

And they are different in a number of ways that argue against genetic crossing.

“The circumstances that gave rise to a mating between a female `i`iwi and a male `apapane are difficult to imagine. `I`iwi are aggressive and socially dominant to `apapane, and the average bill length of `i`iwi is more than 10 mm greater than `apapane. Further, `i`iwi are larger than `apapane, and it is unusual for a female of a larger species to choose to mate with a male of a smaller species,” the authors write.

On the other hand, they are perhaps the most likely honeycreepers to cross.

“`Apapane and `i`iwi are more similar in courtship behavior to each other than with other honeycreeper species and have overlapping breeding seasons,” Knowlton and the team write.

In the forest area where the hybrid bird was found, `i`iwi are about a quarter as common as `apapane. Avian malaria is hitting hard the vulnerable `i`iwi populations, while `apapane, while also impacted, show some resistance to the disease. 

One of the things that isn’t known is whether there might be other such crosses, or whether this bird was able to reproduce. If so, there might be birds in the Upper Waiakea Forest Reserve that are ¾ `i`iwi and `1/4 `apapane, or the reverse.

That’s potentially interesting, because disease-resistant crosses could preserve DNA from the emblematic Hawaiian redbirds.

There is still plenty of mystery in this story. The hybrid bird, known only by its band number of 2551-51657, was released back into the wild after being banded, and has never been seen again.

© Jan TenBruggencate 2014

No comments:

Post a Comment