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"Tyger! Tyger! burning bright / In the forests of the night / What immortal hand or eye / Could frame thy fearful symmetry?" When William Blake wrote these words in the late 1700s, the deforestation and habitat destruction that would decimate wild tiger populations had already begun. In 1900, an estimated 100,000 wild tigers lived throughout much of Asia, from India in the west to Sumatra and Indonesia in the south to Siberia in the east. Today, the ongoing stresses of habitat loss, hunting, and an illegal trade in tiger parts have spared fewer than 7,000 tigers. Of eight traditionally classified subspecies of Panthera tigris, three have gone extinct since the 1940s. In PLoS Biology, evidence is now reported for a new tiger subspecies.
Conservation strategies to combat the grinding attrition of tiger populations are tailored to each subspecies. But several lines of evidence suggest that subspecies designations--based on geographic range and morphological traits such as body size, skull traits, coat color, and striping patterns--may be flawed. To get a clearer picture of the genetic structure of existing tiger populations, Shu-Jin Luo, Jae-Heup Kim, Stephen O'Brien, and colleagues have performed a comprehensive genetic analysis of over 130 tigers.
DNA was extracted from tigers originating in the Russian far east (Siberian, or Amur, tigers), south China, northern Indochina, the Malaya Peninsula, Sumatra, and the Indian subcontinent. Some of the analysis supported traditional classifications--e.g., for the Sumatran and Bengal tigers--but others suggested that the Indochinese subspecies should be divided into two groups, representing a northern Indochinese and a peninsular Malaya population (which the authors designated respectively as P. t. corbetti and P. t. jacksoni, after the tiger conservationist Peter Jackson).
The distinct genetic patterns found in the tiger populations suggest six rather than five living subspecies, with distinct patterns of genetic variability. Whether recent population and habitat declines, as opposed to earlier events, can fully explain these patterns is not clear. But these results offer valuable data for conservation strategies and captive breeding programs.
Citation: Luo S, Kim J, Johnson W, van der Walt J, Martenson J, et al. (2004) Phylogeography and genetic ancestry of tigers Panthera tigris. PLoS Biol 2 (12): e442.
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