Amur Tiger Population Genetic Structure
R. Scudelari
Biology Department, Colorado State University, Fort Collins, CO 80523, USA
Abstract
The tiger population is at a critical point, it can either become extinct in the next hundred years, or through conservation methods, can grow and prosper. The Amur tiger, which has faced drastic geographical reduction, is critically endangered. Populations of the tigers are being separated by human population growth. In order to ensure that the different subpopulations are not diverging from one another, the molecular make-up of the species will be examined. Through this, conservationists will be able to tell whether some of the captive tigers need to be or can be released into the wild to increase the genetic variation, so that gene fragmentation does not occur.
Keywords: Panthera tigris Altaic; gene fragmentation; population genetic structure; genetic variation
Introduction
Panthera tigris (Linnaeus, 1758) the largest catis endangered throughout its territory. Of the nine subspecies existing in the early 20th century, three have been eliminated. When all nine subspecies still existed, tigers covered most of Asia with a population of approximately 100,000 (O’Brien et al. 2005). Tigers now occupy seven percent of their historical range, and in the past decade, the area occupied by tigers has decreased by as much as 41 percent (Dinerstein et all. 2007).
Panthera tigris altaica(Temminck, 1844), commonly known as the Siberian or Amur tiger historically has been found across large portions of northern China, the Korean peninsula, and the southern region of the Russian far east (Heptner & Sludskii, 1972). In the late 19th century, due to human population growth which is linked with habitat loss and pouching of tigers in China, there was a drastic decline in the population. In the early 20th century, a similar scenario occurred in Russia due to the capture of cubs for international zoos and tiger hunting that lead to a population of 20-30 tigers in the 1940s (Heptner & Sludskii, 1972). Conservation measures were immediately started with a ban on hunting and a limiton cub capture. Over the next 55 years the population of wild Amur tigers rose to 428-502 (Miquelle et al. 2007).
Conservation efforts have not only increased the numbers in their natural habitat, but also in the captive population as well. There are now 421 Amur tigers in captivity with the help ofThe Fish and Wildlife Foundation Save the Tiger organization. The current spread of Amur tiger populations in the wild is separated by human populations, creating the concern that there is a restriction in gene flow between the different separated populations of tigers. A restriction in gene flow could cause severe problems in the recovery of the already fragile population. Small populations are more susceptible to losing genetic variation through inbreeding, accumulation of deleterious mutations, and genetic drift (Frankham et al. 2002).
This proposed study will expand on current research by closely examining the genetic make-up of the different population locations in both wild and captive Amur tigers. All these results will be compared to make sure that gene fragmentation is not occurring. Comparing the test results will helpensure that the captive populations’ and wild populations’genetic and morphological make up have not altered from the original Amur tigers. The main goal is to make sure the current Amur population genetic make-up has not significantly changedfrom each other and from the original Amur population.
Materials and Methods
This study will require samples to be taken from the separated Amur tigers in the wild. The subdivisions of the population, due to human population growth, the North American Species Survival Plan tigers, European Breeding Program tigers, and tigers from the zoos in Asia. In order to ensure that the same tiger is not tested twice, each tiger will be tagged and chipped. The purpose of chipping the tiger is to demonstrate if the tigers have crossedover into the other populations or are staying within the subpopulation they reside in. For tigers outside the natural range it is important to know what area they are taken from or from where their ancestors were from.
The skin of the Amur tiger will be sampled in order for this study to be preformed. Three molecular markers will be examined as studied previously including: the mitochondrial DNA (mtDNA), allele variation in the nuclear major histocompatibility complex class II DRB gene, and composite nuclear microsatellite genotype based on 30 loci (Luo et al. 2004). After skin samples are obtained by use of a punch biopsy, the specimen will be placed into liquid nitrogen, and later placed in a freezer at a temperature below 32 degrees Fahrenheit. Guanidine thiocyanate and silica-based purification will be used to obtain the DNA from the dry skin (Luo et al. 2004).
When testing Panthera species mtDNA, it was discovered that it contains a large 12.8 Kb nuclear mtDNA fragment on chromosome F2. It hasexisted there for three million years and been confirmed in ancestral species (Johnson et al. 1996). To overcome this issue, the use of Cymt-specific primer set will be used to complete the tiger Numt and homologous 12.8 kb Cymt sequence (Luo et al. 2004). The genes will then be put through PCR, results will be transferred to a computer system, and then the phylogenic relationship among the mtDNA will be observed. For the microsatellite analysis, 30 loci will be viewed by running the sample through PCRwith fluorescent primers. The resultsbe entered into computers and patterns will betracked. All of the results will be grouped based off of where the tiger was found and compared to all other locations, as well as the data from an ancestral Amur tiger.
Expected Results
After running these three molecular marker tests, it should be clear whether there has been a divergence from the original genes, as well as whether the different subpopulations, both captive and non-captive, have the same genetic make-up. Most if not all of the genes should be seen as not having differed from each other’s subpopulation. It should be expected that the tigers in captivity have some differing genes from wild tigers. However, there should be a huge portion that overlaps if the conservation measures are being properly conducted. The living tigers of today will most likely have differing genes from the ancestral Amur tiger. However, which habitat differs most from the ancestral one (captive or wild) can only be determined by studying the data.
Discussion
This study will be conducted in order to determine the level of genetic variation within Amur tiger populations. Due to historical events in the population, it is important to keep in mind that the Amur tiger population is already known for having a low genetic variation in comparison to the other subspecies of tigers. It will be important to note where the difference are in the genes if any. If there are differences, it will be necessary to examine if this is a new finding or if this was seen in previous studies. If there are new differences within the subpopulations,it can be assumed it is due to the human population growth into their habitat, splitting the population and/or the population adapting to a different environment. If the genetic variation is limited in the wild, the release of captive tigers into the population of wild tigers is essential to the survival of the Amur tiger in the wild. With the use of trackers in the animals, it will be important for conservationists to watch the movement of the wild populations to make sure they are indeed breeding with one another. If there is no breeding between populations, the possibility of a weakened gene pool and mutations exists. Bottlenecking events lead to a low genetic diversity, which leads to adverse effects (inbreeding), and will thenlead to a heightened risk of extinction.
Some possible errors that could occur in the study would include improper scientific technique, which could include errorsrelated to the chemicals or reagents. Improper room temperature could also cause the results to be incorrect. Poor or insufficient samples of skin could also cause problems in the study. The temperature that the skin samples are stored is important also; if not cold enough, the skin cells will die. Should not enough DNA be added to run the PCR, the PCR will not properly operate. Cross contamination on improperly cleaned study devices can also read to invalid results.
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