Siberian Tiger - Genetic Research

Genetic Research

Several reports have been published since the 1990s on the genetic makeup of the Siberian tiger and its relationship to other subspecies. One of the most important outcomes has been the discovery of low genetic variability in the wild population, especially when it comes to maternal or mitochondrial DNA lineages. It seems that a single mtDNA haplotype almost completely dominates the maternal lineages of wild Siberian tigers. On the other hand, captive tigers appear to show higher mtDNA diversity. This may suggest that the subspecies has experienced a very recent genetic bottleneck caused by human pressure, with the founders of the captive population being captured when genetic variability was higher in the wild.

Around the start of the 21st century, researchers from the University of Oxford, the U.S. National Cancer Institute and the Hebrew University of Jerusalem collected tissue samples from 23 Caspian tiger specimens kept in museums across Eurasia. They sequenced at least one segment of five mitochondrial genes, and observed a low amount of variability of the mitochondrial DNA in P. t. virgata as compared to other tiger subspecies. They re-assessed the phylogenetic relationships of tiger subspecies and observed a remarkable similarity between Caspian and Amur tiger indicating that the Amur tiger population is the genetically closest living relative of the extinct Caspian tiger, and strongly implying a very recent common ancestry for the two groups. Phylogeographic analysis suggested that less than 10,000 years ago the ancestor of Caspian and Amur tigers colonized Central Asia via the Silk Road from eastern China, then traversed Siberia eastward to establish the Amur tiger in the Russian Far East. The actions of industrial-age humans may have been the critical factor in the reciprocal isolation of Caspian and Amur tigers from what was likely a single contiguous population.

Samples of 95 wild Amur tigers were collected throughout their native range to investigate questions relative to population genetic structure and demographic history. Additionally, targeted individuals from the North American ex situ population were sampled to assess the genetic representation found in captivity. Population genetic and Bayesian structure analyses clearly identified two populations separated by a development corridor in Russia. Despite their well-documented 20th century decline, the researchers failed to find evidence of a recent population bottleneck, although genetic signatures of a historical contraction were detected. This disparity in signal may be due to several reasons, including historical paucity in population genetic variation associated with postglacial colonization and potential gene flow from a now extirpated Chinese population. The extent and distribution of genetic variation in captive and wild populations were similar, yet gene variants persisted ex situ that were lost in situ. Overall, their results indicate the need to secure ecological connectivity between the two Russian populations to minimize loss of genetic diversity and overall susceptibility to stochastic events, and support a previous study suggesting that the captive population may be a reservoir of gene variants lost in situ.

Managers will be able to selectively breed to help preserve the unique and rare gene variants. This variation may be used to re-infuse the wild population sometime in the future if reintroduction strategies are deemed warranted.