The South Island Robin survives much better now
The South Island and North Island robins of New Zealand are small birds that evolved from Australian ancestors when they reached the distant islands. They are classed in the same genus as the Australasian species of Petroica. There are black, scarlet rose and pink "robins", despite the lack of relationship to any American or European bird.
A bottleneck is a historical time in the life of a species when population falls to a low, at least in some areas. The result is lack of choice of mate, leading to restricted variation within that species. It can be tragic, as in the case of some dog breeds and cheetah, European adders or several other well-known plant and animal species. This is inbreeding at its worst. We know that many endangered species nowadays simply exist as groups of fragmented populations, unable to cross barriers such as roads of cleared forest. Sol Heber and her five colleagues from the University of Canterbury, the University of Cape Town and the German Max Planck Institute worked to resolve inbreeding by introducing "new blood." They publish today in the Proceedings of the Royal Society B: Biological Sciences.
A total of 31 female Petroica were transferred from and to Motuara and Allports islands in the Marlborough Sound of South Island. The history of these populations is that of an original five individuals each, colonising the two islands in 1973. Such a tiny gene pool was not necessarily inbred, but was referred to here as the inbred population by Sol Weber and her colleagues. After 40 years and 10 generations, the two isolated islands supported 360 individuals (adult).
Sol taking a preen sample for testing; Credit: © Sol Heber
The signs that the populations were suffering from inbreeding were reduced hatching success and problems with immune system function. At the end of the experiment in 2010, after one year, the hybrid individuals proved to have significantly lower levels of homozygosity. This seemed linked to juvenile survival. 76% of hybrids survived to one year old, but sadly only 29% of the inbred birds. Just as important, their immune response was tested and proved much more resilient.
Motorua in this experiment received 15 females from Allports Island, while 10 moved to Motuara from Allports. 6 more were added in 2009 as a supplement.
What remains to be seen is what can be performed in future. Where populations can be translocated like this, the technique could prove to be a relatively non-invasive population surgery! In the short term, these fitness increases could prevent extinction. Long-term, the inbreeding would become a problem again.
The solution would be periodic introductions of new stock, but more necessary would be habitat conservation. That old problem is now a worldwide one for many different species. Let's hope these keystone robins provide an impetus for us all to take an interest in preserving species and sub-species that can be helped to survive.
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