Brett Smith for redOrbit.com – Your Universe Online
While many tiger conservation efforts focus on the numbers of a population, maintaining the big cats’ genetic diversity is just as important, according to a report published on Thursday in the Journal of Heredity.
“Numbers don’t tell the entire story,” study author Elizabeth Hadly, a professor in environmental biology at Stanford University, said in a recent statement.
According to the study, because the tiger’s decline has taken place so recently – populations have kept a relatively high amount of diversity. Previous research has shown that the greater gene flow there is among tiger communities, the greater genetic diversity is held and the better the odds of species survival become.
Calling the genetic diversity of a population “the basis for adaptation,” the study team used data on previously sequenced mitochondrial fragments from 5 of the 6 existing tiger subspecies to determine the level of population growth necessary to maintain the current levels of diversity.
The scientists discovered that as populations become more segmented; the pools of each tiger subspecies reduce in size along with genetic diversity. This decrease in diversity can result in reduced reproduction rates, swifter spread of disease and additional cardiac defects, among other issues.
The study team also found that for tiger communities to preserve their genetic diversity for the next 150 years, the tiger populations would have to grow to approximately 98,000 individuals if gene flow across species were detained 25 years. In contrast, the population would have to expand to approximately 60,000 if sufficient gene flow were immediately established.
Unfortunately, neither of these scenarios is realistic due to limiting factors such as prey availability, the study team said.
“Since genetic variability is the raw material for future evolution, our results suggest that without interbreeding subpopulations of tigers, the genetic future for tigers is not viable,” said study author Uma Ramakrishnan, a biology researcher at the National Centre for Biological Sciences in Bangalore, India.
The scientists advised concentrating conservation efforts on facilitating wildlife corridors and other means that allow breeding between different tiger populations, which would maintain genetic diversity more efficiently than increasing population sizes. They added that crossbreeding wild and captive tiger subspecies would be another important focus for tiger conservation.
“Every tiger—including those in zoos, which presently outnumber those in the wild—is important as a potential reserve of the genetic diversity of the species,” the study authors wrote in their conclusion. “Research efforts should aim to estimate ongoing gene flow between protected areas, and immediate efforts toward cross-boundary tiger breeding should be considered.”
“This is very much counter to the ideas that many managers and countries have now – that tigers in zoos are almost useless and that interbreeding tigers from multiple countries is akin to genetic pollution,” Hadly said. “In this case, survival of the species matters more than does survival of the exclusive traits of individual populations.”
The study team cited efforts to conserve Florida panthers as an example of the importance in maintaining the genetic diversity of a population. A program introduced a closely-related subspecies to the Florida population and since the introduction the panther population has risen in numbers and exhibited fewer cases of genetic disorders and poor fitness.
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