Tiger, tiger, burning less bright
The possession of 60% of our wild tigers, Panthera tigris, (in 2012) forms an asset of which India should be proud. These wonderful, impressive "big cats" are currently occupying only 7% of their natural breathing space. Genetically speaking, the fragmentation of each population has grown so that we now have to consider how breeding can use corridors between each group of animals.
Using genetic markers, the authors of this interesting paper found 93% of variation was now absent from modern populations, nationally Genetic differentiation has thereby increased to such an extent that the present policies of simply increasing some populations will not work in the long term. The authors are Samrat Mondol, Michael W. Bruford and Uma Ramakrishnan of the National Centre for Biological Sciences, Bangalore, India and Cardiff University, in Wales. They publish the paper today in the Proceedings of the Royal Society B: Biological Sciences.
Apex predators normally lose variation as the population declines in response to human interference. The paper deals with both mitochondrial and nuclear genetic markers in museum tiger skulls and skins (mainly pre-1950) and modern tigers, which were investigated in Cardiff to avoid any possible tiger or other contamination. Any related animals were removed from the sample to provide more accuracy on possible variation. The Indian government asserted that the tiger population has risen from 1400 to 1700 during the period, 2009-2011, possibly due to hunting controls. But the key investigation here was if variation differs in the sub-continent or between old and new samples.
The results show a great loss in variation of mitochondrial DNA. Only 7% of the "haplotypes" originally present are left, probably because female tigers are quite restricted in their home range. Loss of their habitat has affected the maternally-dispersed mitochondrial DNA negatively. The greatest interest arose from lack of agreement from nuclear samples. More alleles and greater heterozygosity appeared in modern tigers. Checking in north India, the nuclear DNA then showed little change, which gives a clue to the disparity. Peninsular India would possibly provide better agreement in the figures, but most tigers sampled were from the north.
Are the population showing us the red flag that the authors suggest? Or can we overcome the threat of isolation such as that to 2 extremely-threatened groups of tigers living in semi-arid regions? In the latter groups, variation is very low and the necessary conservation monitoring could now concentrate on genetics rather than simple numbers. The connectivity between populations needs to be increased across the sub-continent and even further afield if finance permits.
The honest disagreement between the two parts of this study don't allow us to forget that the population is declining rapidly with almost no out-breeding. Strange results can be expected under such stress and will soon be explained with further samples and comparison with right whales, Scandinavian wolves and several other species. The tiger in India is burning bright, but we will need a lot of help to maintain that orange flame.
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