Kiwi genome reveals nocturnal bird’s colour blindness

TeTuatahianui North Island brown kiwi

The genetic blueprint has been mapped for New Zealand’s national bird, revealing that the kiwi’s adaptation to a nocturnal, ground-dwelling lifestyle has meant poorer eyesight, but super smelling powers.

Published online in Genome Biology, the study by researchers in Germany identified genetic mutations that have deactivated genes related to colour vision, as well as other mutations that have enhanced the kiwi’s sense of smell compared to other birds.

The kiwi is an evolutionary phenomenon, and an endemic species to New Zealand, a land that was geographically isolated after its separation from Godwana 80 million years ago. This isolation makes New Zealand ideal for studying evolutionary processes.

Dr Tammy Steeves, Senior Lecturer in Conservation and Evolutionary Genetics, University of Canterbury, is excited by this genetic blueprint for the threatened North Island brown kiwi. “Of the more than 10,000 bird species worldwide, a mere 50 of them have a readily available genome.”

The kiwi is a flightless bird with low metabolic rate, and the lowest body temperature found in birds. It is chicken size, but lays much larger eggs, and has nostrils at the end of its long beak.

It is already known that kiwi rely heavily on their sense of smell to forage for food at night, but little is known about their genetic evolution.

This new study aimed to improve understanding of kiwi adaptation to a nocturnal, ground-dwelling lifestyle, and the genomic changes involved in this adaptation.

Researchers wanted to understand the genetic basis of kiwi traits, including the kiwi’s sensorial adaptation, and which variants are responsible for the absence of wings, lead author Diana Le Duc told biotech company Illumina.

The kiwi is the smallest and only nocturnal member of the ratite family that includes the extinct New Zealand moa and Madagascan elephant bird, and the extant Australian emu, African ostrich, New Guinea cassowary, and South American rhea.

A previous study identified kiwi as diverging from the Madagascan elephant bird 50 million years ago, suggesting that ratites dispersed by flight.

There are five species in the kiwi genus Apteryx.This new study’s international research team, led by Torsten Schöneberg of the Institute of Biochemistry of the Medical Faculty at the University of Leipzig and Janet Kelso of the Max Planck Institute for Evolutionary Anthropology, have sequenced the genome of the brown kiwi, Apteryx mantelli.

Kiwi have small eyes compared to other nocturnal species, but they have a higher proportion of rods than cones, which is usual in nocturnal species. Colour vision in the green and blue range was found to be absent, and this genomic change was timed at around 30-38 million years ago.

Researchers in this study found that genomic changes in kiwi vision and smell are consistent with changes thought to occur in mammals as they adapt to a nocturnal lifestyle.

This newly sequenced, assembled and annotated North Island brown kiwi genome will provide data for comparison with other extinct and extant diurnal ratites.

DNA analyses of two kiwi individuals show there could be little genetic variability in the population, which could further impact the species, predicted to become extinct within 50 years at the current annual population decline of 2 percent.

The NZ government’s budget announcement of funding for kiwi conservation will help with predator control as well as breeding programs, which will benefit from the extensive genome information.

From this high quality genome, species-specific genomes could be developed, “to better inform conservation management strategies to minimise the loss of genomic diversity, particularly for threatened birds like the North Island brown kiwi,”said Dr Steeves.

Image credit: North Island brown kiwi by Maungatautari Ecological Island Trust (http://www.maungatrust.org/news/default.asp) [Public domain], via Wikimedia Commons

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Tracy is a freelance writer with special interest in scientific research and news on wildlife, the environment, animal welfare, and mental health. Follow my 'Nature in Mind' blog at www.tracybrighten.com and Twitter @TracyBrighten1

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