New hope for endangered animals

By Paul Harper

South Island robin. Photo / Jim Eagles
South Island robin. Photo / Jim Eagles

A University of Canterbury study offers new hope to endangered animals suffering the effects of inbreeding.

The study, undertaken by PhD graduate Dr Sol Heber and Associate Professor Jim Briskie, has found that interbreeding two separate populations of severely inbred South Island robins (Petroica australis) can reverse the negative effects of inbreeding and increase genetic diversity.

Associate Professor Jim Briskie said one of the consequences of endangered animals declining to what is called a "population bottleneck" is that small populations cannot help but mate with relatives.

As a result a population may lose a lot of genetic variation.

"That kind of inbreeding can lead to what's called inbreeding depression. In the case of birds, they have trouble producing eggs that are viable, the males have trouble producing viable sperm, their immune systems can be compromised ...the same sorts of things happen in humans as well - that's why you're not allowed to marry your sister, because the kids don't turn out right."

Briskie said several overseas studies have shown the introduction of outbred individuals into small inbred populations can reverse the negative effects of inbreeding and increase genetic diversity.

The benefits could be seen within the first generation of hybrid animals, he said.

"But the problem for endangered animals is there is no other population you can get individuals from. That's pretty true in New Zealand, a lot of our birds are just in small populations on isolated islands. So we're left with a dilemma - they're all inbred."

So Briskie and Heber exchanged 31 individuals between two inbred populations of South Island robin, a native species which is not endangered. The populations, one on Allports Island and the other from Motuara Island, descended from only five birds each. The small populations had been taken to the islands in 1973 by conservationists as practice for the relocation of the last five remaining Chatham Island black robins.

"Since the 70s they've both been left alone more-or-less, and a number of generations have passed," Briskie said. "But because they have only five founders, both these populations have low levels of genetic diversity. So they suffer from this inbreeding depression - they have trouble hatching their eggs, they produce a lot of dud sperm, their immune system is very weak.

"So we crossed those two populations, we moved just females between the populations - we took a female from a pair and exchanged it in a reciprocal way with a female from another pair.

"Almost immediately, within the first generation and continuing on with subsequent generations, there were dramatic changes. They no longer had trouble hatching eggs, their sperm was better, there was an amazing increase in the survival of the young."

The hybrid birds were also more likely to find a mate compared to their inbred counterparts.

The findings have been published in the journal Proceedings of the Royal Society B: Biological Sciences.

Briskie said a similar experiment undertaken in the lab with fruit flies had the same results.

The technique of reciprocal translocation of inbred populations has not been tested with other birds. However, Briskie believed it could benefit endangered New Zealand animals - and not just birds but also skinks and geckos and even plants.

"The reason we did it is to demonstrate there's no lost causes with endangered birds. Even if they are suffering from inbreeding depression there is something that can be done, perhaps, to alleviate some of those problems they are experiencing, whether it is problems hatching eggs, problems with their immune system, or whatever the case may be."

- nzherald.co.nz

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