How kiwi birds adapted to their nocturnal lifestyles

By sequencing the genome of the kiwi bird for the first time, researchers have found that these flightless, New Zealand-based ratites posses altered DNA that eliminates color vision and cause it to have a modified sense of smell, according to a new Genome Biology paper.

These genes, lead author Dr. Diana Le Duc from the University of Leipzig and the Max Planck Institute for Evolutionary Anthropology in Germany and her colleagues report, helps to explain the nocturnal behavior of the kiwi, which are also well known for their well developed sense of smell, their low metabolic rate and the size of their eggs relative to body size.

Dr. Le Duc’s team sequenced a pair of North Island brown kiwi, marking the first time that the birds have had their genome sequenced and revealing that their genomes are among the largest bird genomes sequenced to date. Furthermore, their work identified several of the evolutionary changes behind the kiwi’s unique adaptations to nocturnal behavior.

She and her co-author Torsten Schöneberg of the Institute of Biochemistry at the University of Leipzig told redOrbit that it took them nearly four years to fully assemble and annotate the kiwi’s genome, and that despite several attempts to fill in most of the sequence gaps, some remained.

Loss of color vision was the biggest surprise

According to the authors, this study marks the first time that researchers have found evidence that kiwi lack color vision, and that their olfactory receptors likely detect a larger range of odors that help the birds forage during the nighttime. These adaptations appear to have occurred some 35 million years ago, shortly after the birds first arrived in New Zealand.

The gene responsible for black and white vision in the kiwi, rhodopsin, was found to be close to that found in other vertebrates, the researchers noted. They also identified mutations in the green and blue vision receptor genes which may render the kiwi unable to see in those hues as well.

Drs. Le Duc and Schöneberg said that “the loss of color vision, especially the mutations that led to the inactivation of the receptors” was “the most surprising finding” of their research. This was “further supported when we sequenced the green opsin in other kiwi species” and found that “all of them had the same inactivation mechanism,” but no other ratites did.

Findings important to kiwi conservation efforts

Despite of efforts to protect the species, North Island brown kiwi continue to face a high risk of extinction, the researchers noted. They compared the sequence of two individuals and found that the diversity of their genomes appeared to be as low as that of inbred birds – a sign of the serious threat to the kiwi species as a whole, Dr. LeDuc explained in a statement.

She and Dr. Schöneberg told redOrbit that their findings “could be very relevant to conservation efforts, especially because as far as we know for the moment kiwi eggs are successfully collected from the wild, assisted in the hatching process, and chicks are released back to the wild at an age when they can successfully protect themselves from predators like stoats.”

“Knowing the diversity of the kiwi population can be achieved much easier using the genome as a reference to which other sequenced kiwi birds can be compared and an informed decision can be made in regard to the need of mixing different populations to reduce inbreeding,” they added.