Black robin conservation efforts allowed survival of the not-so-fit

December 12, 2013

University of Canterbury (UC) researchers have found that conservation efforts in the 1980s to save a critically endangered New Zealand bird inadvertently risked compromising the long-term viability of the species.

The study, conducted by UC researchers Dr Raaz Sainudiin, Dr Marie Hale, Dr Jim Briskie, Dr Anthony Poole and former UC academic Dr Melanie Massaro, documents the unintended consequences of conservation measures taken to save the Chatham Islands black robin from extinction.

The findings of the research were recently published in the scientific journal Plos One.

Dr Massaro, who is now based at Charles Sturt University in Australia, says, in general, conservation efforts to save endangered species from immediate extinction focus, by necessity, on increasing productivity and reducing mortality.

However, such efforts may unintentionally relax natural selection, potentially allowing the ``survival of the not-so-fit”.

Dr Massaro says in 1980 the black robin population was reduced to five individuals, including only a single breeding pair.Following this bottleneck, some females were observed to lay eggs on the rims or edges of their nests. These rim eggs were not incubated and always failed to hatch. 

``To avoid imminent extinction and to expedite population recovery, rim eggs were repositioned inside nests by conservation authorities, yielding viable hatchlings,” she said. 

``Repositioning resulted in rapid growth of the black robin population but, by 1989, more than 50 per cent of all females were laying rim eggs and the situation appeared to be getting worse. In 1990, however, repositioning of rim eggs ceased, allowing natural selection to again operate unhindered.”

Dr Marie Hale says their research, using an exceptional species-wide pedigree of black robins, found that rim laying is caused by a genetic mutation and passed from parents to offspring. 

``The behaviour appears to be controlled by a dominant allele so that even if only one copy of the mutation is inherited, a female will lay at least some of her eggs on the rim of her nest. Data that we collected after human intervention ceased shows that the frequency of rim laying has strongly declined, confirming that in the absence of human interference this behaviour is being selected against and slowly disappearing.

``Human intervention, by removing selection against rim-laying individuals, facilitated the spread of this inherited egg-laying behaviour within the extremely small population.

``This episode yields an important lesson for conservation efforts worldwide: accidental fixation of deleterious mutations through hands-on conservation efforts could render small threatened populations completely dependent on humans for reproduction, irreversibly compromising the long term viability of populations humanity seeks to conserve.”

``Fortunately for the black robin, human intervention ended in time to prevent fixation and allow natural selection to once again favour the survival of the fittest,” she says.

``In light of the increasing number of endangered species under management in New Zealand and around the world, understanding the long-term impacts of conservation activities on the genetic health of populations is important to prevent future extinctions,” Dr Massaro says.

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From left to Right: Dr Marie Hale and Dr Melanie Massaro.

ENDS

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